Guide to Food Transport - Fish, Meat and Dairy Products

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FISH, MEAT AND DAIRY PRODUCTS

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GUIDE TO FOOD TRANSPORT FISH, MEAT AND DAIRY PRODUCTS

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© 1990 by Mercantila Publishers as Lay-out and artwork: Mercantila Publishers as, Copenhagen Printed in Denmark by Jydsk Centraltrykkeri A/S ISBN 87 89010 97 3 Distribution by Mercantila Publishers as 18 Upsalagade DK-2100 Copenhagen Denmark Tel: +45 3543 6222 Fax: +45 3543 5151

All rights reserved. No parts of this book may be reproduced, stored in a retrieval system or transmitted in any form, or by any means - electronic, mechanical, photocopying or other wise, without the prior written permission of Mercantila Publishers as

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CONTENTS

CONTENTS Preface

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CHAPTER 1 General about Foods

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1. Chilling injury

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2. Controlled atmospheres

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3. Relative humidity

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4. Packaging

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5. Refrigeration

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6. Regulations

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7. Temperature monitoring and temperature measurement

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CHAPTER 2 Transport conditions

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1. General information on transport

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2. Mechanical refrigeration

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3. ISO intermodal containers

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4. Primary distribution vehicles (trailers)

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5. Other types of refrigeration systems

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6. Other types of transport equipment

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7. Code of good transporting practices

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CONTENTS

CHAPTER 3 Practical storage life (PSL) of foods

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1. Quality influencing processes

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3. TTT-PPP concept

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3. Deep frozen foods

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4. Frozen foods

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5. Chilled foods

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CHAPTER 4 1. Liability for carriage of goods

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2. Insurance

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3. Instructions for the carrier

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CHAPTER 5 Definitions and explanations

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Index

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PREFACE

PREFACE The GUIDE TO FOOD TRANSPORT, Meat, Fish and Dairy products, provides information and guidelines to help assure that perishable foodstuffs reach their intended destination in the best condition possible.

for avoiding such situations and the pursuing cargo loss claims. As such, it will be invaluable to people in all branches of the perishable food transportation industry, i.e. shipowners, carriers, shipping agents, consignors and insurance agents.

In July 1989 we published GUIDE TO FOOD TRANSPORT, Fruit and Vegetables. The main part of this book describes one hundred of the most important products in the fruit and vegetable category. It was quickly realized that there was a definite need for a book describing the other perishable foodstuffs, i.e. chilled and frozen meat, fish and dairy products.

In preparing this new book it was decided to put all the different perishable foodstuffs into 16 different product groups. The description of these deep (quick)frozen, frozen or chilled groups is found in sections 3, 4 and 5 in chapter 3. For each product information is given on relevant legislation, minimal requirements for raw materials, processing and packaging, the storage life at different temperatures, recommended or required transport temperatures, and sensitivity to temperature and foreign odours. Section 3 also includes general information about quality influencing factors, storage life, calculation of quality loss etc.

Previous literature on this subject was quite technical, aimed at experts who already possessed some background knowledge. This new book, and its predecessor, is written so that they can be easily understood and used by all. Improper or careless handling of perishable foodstuffs during manufacture, storage and transportation can lead to damaged cargoes (or even food poisoning) and extensive losses. The inadvertent destruction is often due to incorrect temperatures during manufacture and transport. The GUIDE TO FOOD TRANSPORT, Meat, Fish and Dairy products, provides suggestions and background information

Chapter 1 summarizes important aspects in connection with foods such as packaging, legislation, temperature measurements etc. Chapter 2 gives a description of transport equipment, mainly trailers and containers. This includes refrigeration units, air circulation, temperature control systems, loading and unloading. Chapter 4 deals with the most important

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PREFACE

aspects of insurance, including information on the necessary procedures in case of transport damage. Chapter 5 gives definitions and explanations on some of the terms used in the book. Most of the book was compiled from information supplied by Leif Bøgh-Sørensen, Danish Meat Products Laboratory, Ministry of Agriculture, who has experience in all aspects of food technology. Mike Cowley (Cowley Industrial Consultants Ltd.) was givin the responsibility of ensuring the correctness of the text. Information on legislation was given by food scientist Linda Jensen, and on fish and fish products by food scientist Helle Emsholm. In-

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formation and advice on transport equipment was given by several persons, especially Mogens Eilsø and Hans Chr. Lindhardt. The chapter on insurance is based on material, prepared by Theo Koch & Co, Average agents, Copenhagen. A number of the photographs were supplied by the Danish Meat Research Institute or from Frigoscandia AB. We would like to express our sincere thanks to all contributors who have made the publishing of this book possible.

September 1990 Mercantila Publishers as

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1 CHAPTER

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GENERAL ABOUT FOODS

GENERAL INFORMATION ABOUT FOODS The information contained in this book covers frozen foods and chilled foods. Produce for consumption as fresh fruit or vegetables is not included, as they are dealt with in the book GUIDE TO FOOD TRANSPORT, FRUIT AND VEGETABLES. Definitions and explanations of some of the terms used in this book can be found in chapter 5. Chapter 1 comprises the following sections: Section 1 Chilling and freezing injury. Section 2. Controlled atmosphere. Section 3.1 Relative humidity (RH), 3.2 water loss Section 4. Packaging, including 4.1 Inner packaging. 4.2 Outer packaging. Section 5. Refrigeration Section 6 Relevant regulations on transport equipment, including 6.1 The ATP Agreement 6.2 Foodstuffs, especially in the EEC. 6.3 Regulations on packaging materials. 6.4 Irradiation. 6.5 The activities of Codex Alimentarius are outlined. Section 7. Temperature monitoring and temperature measurement including 7.1 Air temperature measurement.

7.2 Product temperature measurement. 7.3 Temperature recording during transport. 7.4 Temperature measuring instruments. 1. CHILLING INJURY Chilling injury is a very important quality factor for fresh fruit and vegetables. For several commodities, quality and storage life will be reduced considerably when the temperature of the food product is lowered to, or below, a critical temperature. This critical temperature is usually the freezing point of the liquid within the fruit, usually just above 0°C. However for some fruits with a high sugar content, such as citrus fruit, it is above 8°C, for bananas it is above 12°C. For the products dealt with in this book, chilling injury seldom plays a major role. This means that for practically all chilled foods the optimum storage and transport temperature is marginally above the freezing point of the food product. For most raw foods the freezing point is -1.5°C to -2°C , and the ideal temperature for these chilled foods would be -1°C with a minimum of fluctuations, i.e. -1°C +/- 0.5°C.

Freezing injury Freezing injury occurs when the food is exposed to freezing temperatures for more than a short time. For most meat, poultry and fish products, the freezing process makes very little difference in the

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CONTROLLED ATMOSPHERES (CA)

eating quality of the foodstuff. There would be no loss of quality if the product temperature was accidentally reduced to below the initial freezing temperature for example during transportation. However, the problem is that freezing during transport will normally be a very slow process, so slow that severe quality degradation could occur. The significance of freezing time and freezing rate is discussed in chapter 3 section 3. 2. CONTROLLED ATMOSPHERES (CA) In normal atmospheric air - comprising approximately 21% oxygen, 0.03% carbon dioxide and the rest nitrogen - most quality influencing processes advance readily. In the case of chilled foods most microorganisms demand a certain amount of oxygen to grow. The growth of microorganisms eventually leads to spoilage of the food product, see chapter 3 section 1.1 Microbiology.

A method used to prevent or reduce the rate of microbe growth is to alter the composition of the atmosphere surrounding the food. This is normally done by reducing the oxygen content, or increasing the carbon dioxide content, often both. 2.1 CA-storage Storage in controlled atmosphere, usually referred to as CA-storage is used to a large extent for fresh fruits and vegetables, see GUIDE TO FOOD TRANSPORT, FRUIT AND VEGETABLES. For the products dealt with in this book CAstorage is hardly ever used. The use of a controlled atmosphere in packaging of foodstuffs is discussed in section 4. 2.2 Modified Atmosphere (MA) Modified atmosphere as defined in

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GUIDE TO FOOD TRANSPORT, FRUIT AND VEGETABLES is not relevant to the foods included in this book, as they do not respire and cannot change the composition of the surrounding atmosphere. However, in vacuum packaging, for example fresh meat, the concentration of carbon dioxide will increase considerably, to more than 50%, due to enzyme activity and/or microbiological growth. The term Modified Atmosphere Packaging (MAP) is used , see section 4.1.3 below.

3. RELATIVE HUMIDITY (RH) - WATER LOSS

3.1 Relative humidity (RH) The fact that water is suspended in air is illustrated in our day to day life by mist, early morning dew and our breath condensing in cold air. It is not important to understand the physics of water vapour other than the fact that the relationship between temperature and the amount of water air can hold is non-linear. The psychometric chart, see fig.1.1, is a way of displaying the conditions relating to water in air at a specific atmospheric pressure, usually sea level. The dry bulb temperature, i.e. the temperature measured by a normal thermometer, is shown on the horizontal line, the wet bulb temperatures are those on the lines falling to the right. The relative humidity ( RH ), also referred to as humidity percentages are the lines curved up, and the vertical axis is the humidity ratio, i.e. the content of water in 1 kg of dry air. Relative humidity ( RH ) is a commonly used term to describe humidity of air, but without knowing the corresponding temperature (dry bulb temperature). It has no precise meaning. It is more meaningful to

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RELATIVE HUMIDITY (RH) - WATER LOSS

025 Sea Level

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Dew Point 14°C

100

°C 20

°C

50

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60

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Bu

lb

We t

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Bu

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010

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midit

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Humidity Ratio (kg/kg)

Psychrometric Chart

RH

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°C

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Fig 1.1 Psychrometric chart showing humidity and temperature relationship

The RH can be found at the point of intersection between the dry bulb and wet bulb temperature lines, for example:

tain much more water than cold air with a similar RH. For example, air with 90% RH contains 10 g water/kg air at 15°C, and 5 g water/kg air at 5°C, see figure 1.1. From other diagrams or tables it can be found that air at 20°C and 90% RH contains as little as 0.6 g water/kg air. Therefore, a lower air temperature will reduce dehydration of foods.

A dry bulb temperature of 25°C and a wet bulb temperature of 18°C will give a relative humidity of 50% (point A). By extending a line horizontally from point A to the right hand scale (point B), you will be able to read off the humidity ratio, 0.010 kg per kg of dry air, which means that 1 kg dry air contains 10 g of water vapour. In a refrigerated storage room or a transport vehicle the RH is used to indicate the rate of evaporation that the commodities are subjected to. However this is not an accurate method as warm air may con-

In cold storage rooms and transport equipment, the air temperature varies. The air delivered from the refrigeration unit will take up heat from the produce and other sources, so the air returning to the refrigeration unit will be some degrees warmer than the delivery air. The air closest to the evaporator, i.e. the delivery air, will normally have an RH close to 100%, while the circulating air will have a lower RH. This indicates that there may be considerable differences in RH in different locations in the same room.

talk of humidity ratio, that is the ratio of the weight of water in suspension in the air, to the weight of the dry air. This can best be explained by an example and by reference to fig.1.1.

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RELATIVE HUMIDITY (RH) - WATER LOSS

If the air at point A was cooled, the horizontal line from point A should be extended to the left, progressively increasing in relative humidity until it reaches 100% at 14°C (point C). Any further cooling would result in water condensing out of the air (dew would form). The dew-point is 14°C. To avoid free water forming on foodstuffs, packagings or inner surfaces of the transport equipment, the air circulating over cold surfaces must not be warmer or have a higher RH than the corresponding point between A and C. The important point to note here is that with perishable foods requiring a temperature near 0°C, and a high RH, the circulating air must be cooled to a sub zero temperature, about -2°C, by means of the evaporator. Unfortunately this will cause water condensation at the surface of the evaporator subsequently lowering the RH. One way of keeping the humidity high is to ventilate the room with warm air from the outside. For example, air from outside with a dry bulb temperature of 25°C and wet bulb temperature of 18°C (point A) entering the vehicle or storage room where the internal temperature is 0°C and RH 95%, will add moisture as the air is cooled to 14°C (point C) when it will loose water and will continue to do so until its temperature reaches 0°C. The moisture content of the newly introduced air dropping from 10 g to 4 g per kg, will add 6 g water for each kg of outside air introduced. The limiting factors to using outside air to raise humidity are power consumption and having the external air in the appropriate condition. 1 kg of atmospheric air has a volume of about 0.8 cubic metres. 3.2 Water loss Water loss (dehydration, desiccation or evaporation) can result in quality deterio-

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ration in chilled and frozen foods. Weight loss is normally of far greater importance due to the high monetary value of most chilled and frozen foods. Therefore, an ever increasing number of chilled and frozen foods are protected against dehydration by means of appropriate packaging. Water loss from unwrapped foods can be reduced by maintaining the correct temperature and humidity in the storage room. Evaporation of water from food occurs primarily because of the difference in vapour pressure between the surface of the food and its surrounding atmosphere. As mentioned above, most chilled and frozen foods are packaged for protection against water loss during storage and transport. The air surrounding unwrapped deep frozen foods is -18°C or less and can contain very little water. In practice, very little is done to adjust the RH in unwrapped frozen foods, either in freezer storage rooms, or in transport equipment. Frost formation inside the packaging. Even when a package with a low water vapour permeability is used, dehydration of the frozen product still occurs if the package does not fit tightly around the product. The main reason is that, in practice, the temperatures will never be constant, but always fluctuate. The water removed from the food itself remains inside the package as frost. The mechanism of the interior frost formation in a package which does not fit tightly around the product is as follows: - The layer of air between product and packaging is subject to temperature variations. As the temperature outside the package decreases, the temperature of the inner surface of the packaging will drop below the product surface tempera-

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RELATIVE HUMIDITY (RH) - WATER LOSS

ture and ice from the product will form and condense on the inside of the package. - When the outside temperature increases, the process is reversed and the water vapour will condense on the product surface. - As the cooling-heating cycle recurs, the ice crystals on the product surface tend to follow package temperature more closely than the mass of the product, and this results in further sublimation of ice from the product. Frost in packages can amount to 20% or more of product weight. Since the desiccation of the surface layers results in an increased surface area and thus greater access to oxygen, the rate of the quality degradation of the food at the surface may also increase. For retail packed frozen foods such as vegetables, meat balls, etc. the problem is difficult to solve, as it is not possible to pack them so as to remove the air between the particles. Such products are very susceptible to internal frost formation, especially if they are allowed to spend a long time in the outer layers of display cabinets. By using laminates that include a layer of aluminium foil, internal frost formation can be reduced considerably. Freezer burn. Unwrapped frozen foods continue to lose weight through desiccation during storage, but lower storage temperatures result in less weight loss. For packaged frozen foods, damage to the packaging material will cause an increased rate of dehydration. Light (white) spots on the surface of frozen foods are caused by local dehydration and can result in an unacceptable appearance. Light spots normally disappear on thawing and cooking and have no influence on taste or texture.

Severe dehydration leads to “freezer burn”, i.e. formation of greyish zones at the surface due to cavities forming in the superficial layer. Freezer burn causes the lean surfaces of meat to become rancid, discoloured and physically changed. Freezer burn is irreversible, does not disappear on thawing and cooking, and signals undesirable changes in taste and texture. Meat, poultry, fish, game in particular can be severely affected by freezer burn. Temperature fluctuations. The effects of temperature fluctuations depend on the average storage temperature. The higher the storage temperatures the more effect the temperature fluctuations will have on ice sublimation pressure and the growth of ice. Minimum desiccation is achieved at colder storage temperatures, i.e. -18°C or colder, with a minimum of fluctuations. As mentioned above, evaporation of water from the food surface depends on the difference in water vapour pressure. The water vapour pressure, as well as the water content in the air decreases with temperature, see fig. 1.1. Therefore, rapid cooling of food products, especially unwrapped food products, to their required storage temperature is very important. The colder the food surface, the smaller the evaporation effect, hence a smaller weight loss. When cooling either in the chilling process or the freezing process the food surface temperature will drop faster than the internal temperature. This is an advantage when it comes to weight loss, as evaporation depends on the product surface temperature. An ultra rapid chilling process results in minimal weight loss, and is an advantage in relation to microbiology. The faster the temperature is

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PACKAGING

lowered, the faster the growth of microorganisms is retarded. As discussed in chapter 3 section 5.0, a very rapid chilling process may result in problems in quality such as toughening of meat due to cold shortening.

4. PACKAGING Packaging for foodstuffs is divided into two categories, inner and outer packaging. The inner packaging is in direct contact with the food product. It can be a package intended for the final consumer; common terms are consumer pack, sales packaging, retail packaging, or primary packaging. This includes packaging intended for catering and larger consumers such as canteens, hospitals,etc. Inner packaging is also used for packaging of food intended for further processing. Outer packaging normally contains a number of inner packagings. Common terms are outer cases, transport packaging, transport carton, shipping container, secondary packaging, etc.

4.1 Inner packaging Packing of products in consumer packs has disadvantages as well as advantages. Advantages: Protects against contamination - Reduces or prevents dehydration Facilitates sales distribution - Necessary for hygiene purposes for foods to be sold in self-service shops, such as supermarkets - Necessary to attach information prescribed in labelling directives etc. and convenient to attach consumer information and instructions Disadvantages: Cost - May slow down the chilling process if the food has not achieved the correct temperature prior to the packing process.

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Choice of packaging should be based primarily on the requirements of the individual product. The nature of the food, product composition, the temperatures it is likely to experience, the expected storage life should be taken into consideration. Some important aspects of packaging such as sales appeal, colour and “marketing” issues are not considered in this book. A wide range of materials and packaging forms are available. The most predominant form of consumer packs are plastic bags or “foodtainers” a tray made of wood-pulp or plastic, overwrapped with a plastic film. 4.1.1 Important properties of packaging materials. The most important properties of packaging materials to be used for food products are: Water Vapour Permeability - Permeability to water vapour, called Water Vapour Transmission Rate (WVTR). For almost all the products dealt with here, WVTR of the packaging material, and of the packaging itself, should be low or very low. Plastic laminates containing an aluminium foil layer have such a low WVTR that there is hardly any water vapour penetration. Gas Permeability -Permeability to gases, especially oxygen and carbon dioxide. For a number of frozen or deep frozen products it is necessary to use a packaging material with low oxygen permeability in order to prevent or reduce the development of rancidity. Rancidity is an oxidative process, hence there must be oxygen present to allow it to start, see chapter 3 section 1.2.

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When vacuum-packaging is used, it is necessary to use a packaging material with an oxygen permeability less than 7090 ml/m2/day x bar, measured at room temperature. For foods requiring extra protection against oxygen, packaging materials with an oxygen permeability of 10 ml/m2/day x bar or lower are used. For packaging materials to be used for MAP,the permeability to oxygen and carbon dioxide must be equal to or lower than the permeability of plastic materials used for vacuum packaging. Physical properties These comprise several different characteristics such as burst strength, tensile strength, elongation, elasticity, etc. The packaging material used must be able to withstand the conditions it experiences in the cold chain, such as drops, shocks, vibrations, etc. At present, internationally recognized and standardized methods are not available, therefore it is normally necessary, and always advisable, to carry out transport tests in order to ensure that the inner packaging has sufficient strength. For deep frozen goods the material must be able to withstand temperatures as cold as -40°C without becoming brittle. In some cases, liquid nitrogen or solid carbon dioxide is used as a refrigerant, and the packaging material must withstand temperatures as low as -50°C or even lower. The trend towards ready-to-eat dishes means that an increasing amount of packaging material as well as withstanding extremely cold temperatures must also be able to tolerate high temperatures, e.g. 100°C for “Boil-in-the-bag” pouches, 200°C or even higher for oven cooked consumer packs. Hot fillings are used for some foods. This

means that the food (usually liquid or semi-liquid ) is put into the package while still hot, often over 90°C. Obviously, the packaging material must be able to withstand this process. Machinability The term “machinability” is difficult to define, but as packaging machinery is often very expensive, it is an important factor in the choice of a potential new plastic that it can run on the existing packaging machinery at least the same speed and with lesser failures than the material it is to replace. Migration. As stated in section 6.3, several countries have legislation on packaging, including maximum permissible limits for migration of additives from the packaging material into the foodstuff. 4.1.2 Packaging materials. For chilled and frozen foods the most commonly used plastic materials are: Polyethylene(PE) The low density form (LDPE) has a relatively low WVTR, but a high permeability to oxygen. The heat sealability is excellent, and PE is comparatively inexpensive. It is frequently used in laminates as the inner layer in contact with the foodstuff. Polyamide(PA) or Nylon This plastic material has good strength and moulding properties, and relatively low permeability. It is used in many laminates, e.g. for use in vacuum-packaging or deep-drawn articles. Polyester(PET) This film withstands high temperatures, some types up to about 240°C. PET may be used for double cooked consumer

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packs. It has very good mechanical properties, but is rather expensive.

well be one of the layers. Paper is also used as a layer in some laminates.

Polyvinyl chloride (PVC). This film has good mechanical properties, good optical properties,and is rather inexpensive. Soft PVC, i.e. PVC where a certain amount of plasticiser are incorporated, has high permeability. Plasticised PVC is used for retail packaging of several foods, e.g. meat, poultry, fruits. Other types of plasticized PVC are used for rigid or semi-rigid containers, often thermoformed.

The different layers may be held together by means of adhesives, or they can be produced as a co-extrusion. By using laminates it is possible to combine the desirable characteristics of different plastic materials at a reasonable cost. Today it is possible to manufacture packaging materials with the desired permeability properties. Beside these plastic materials, there are some other packaging materials used for chilled and frozen foods.

Aluminium foil. The use in laminates is mentioned above, but aluminium foil, in the form of trays, is used for a range of foods, for example for ready-to-eat meals to be heated in a conventional oven and for meat products such as pate. Paper. Paper Is used as a layer in some laminates, for example in composite cans, used for frozen concentrated juice etc. As greaseproof paper is it used for dairy products such as butter and margarine, and for animal fats such as lard. Barrier-layers. The two best known barrier materials are PVDC and EVOH. Both plastic materials have very low oxygen-permeability and are used as barrier-layers in laminates intended for products where the oxygen diffusion must be minimal, for example in plastic materials intended for use in vacuum-packagings of oxygen sensitive foods, or for use in MAP. Laminates. A laminate comprises several layers, normally of different materials. In most cases all layers will be plastic materials, but aluminium foil (or a metallizing sheet) could

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Cartons. Consumer packed frozen foods and ice cream, milk etc. are often packed in cartons which are coated with plastic (normally PE). The paperboard used is described in section 4.2.3 below. Metal cans. Metal cans are used for some perishable products that should be kept at 5°C or below, for example “keep refrigerated” cured meat products which have been pasteurized (a centre temperature of about 72°C), resulting in a practical storage life (PSL) of 6 months or more at 5°C or below. Plastic packaging has replaced cans for many of these products. 4.1.3 Packaging forms Consumer packs of frozen and chilled foods are found in various forms. Basic package forms may be grouped in three major categories: rigid, semirigid, and flexible. Rigid packages are formed into a definite shape from sufficiently strong materials, so that they retain their shape when filled. The materials normally used are metal and glass. Semirigid packages are formed into a definite shape but are made from weaker

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PACKAGING

materials, so they can be distorted by the application of moderate force. Semirigid packages are made of metal, such as aluminium foil, plastics and paperboard. Flexible packages are made from flexible materials such as plastic, paper, thin metal sheet etc., and generally their shape conforms to the shape of the product. They may be distorted with ease. Rigid materials become more and more flexible when fabricated to thinner and thinner sections, and the distinction between rigid and semirigid and between semirigid and flexible packaging forms is often hard to determine. There is some overlap in the naming of certain packaging.

material, but combinations are being used in an increasing amounts. A number of chilled and frozen foods require protection against dehydration but do not need a special barrier against oxygen. For such foods a pouch made of PE, for example, would be sufficient to secure the expected storage life. Several frozen as well as chilled products belong to this category. Plastic bags and pouches are often heat sealed. The package is closed by means of heat and pressure in such a way that it is completly sealed so micro-organisms cannot penetrate the package. A heat seal of this type is sometimes referred to as hermetically sealed.

Wrappers The simplest type of flexible package is the wrap, where a sheet material is used to enclose a quantity of product. Greaseproof paper is very useful as a wrap for butter and margarine. When meat, fish and many other foods must be transported in bulk over long distances, wrappers are seldom used.

Vacuum-packaging When the package has been filled with foodstuff, the air is drawn out, and the package is sealed (usually heat sealed). With a flexible package, the plastic material will be pulled against the foodstuff. As mentioned above, a packaging material with a low oxygen permeability must be used. In this way, the food is protected against oxygen in the atmosphere, and the quality degrading processes should proceed at a reduced rate, resulting in an increased storage life.

Overwrapped trays In supermarkets, fresh meat and poultry is traditionally displayed in trays made of wood pulp or a rigid plastic, some times called a “foodtainer”. The foodtainer and the meat is then overwrapped with a plastic film with high permeability to oxygen. Fresh fruit and vegetables are also marketed in this way. In some countries it is a legal requirement that foodtainers used for fresh meat shall be transparent. In these places foodtainers are made of a transparent plastic. Bags, pouches. Plastic bags and pouches are the most widely used consumer pack. They may be manufactured from a single plastic

It is recommended that at least 95% of the air should be removed from the package during the vacuum process. The small amount of air remaining inside the package will have it’s oxygen consumed by enzymes and micro-organisms with a byproduct of carbon dioxide. For foods such as fresh meat the concentration of carbon dioxide in the small amount of air remaining in the package is often well above 50%. This contributes to the long storage life of vacuum-packed beef. Plastic bags and pouches are often evacuated in this way as are most other packaging forms.

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VSP (Vacuum Skin Packaging) A special type of vacuum-packaging is used for some foods. A barrier plastic material with a low melting point is softened by heating before applying a vacuum and sealing the package. During this operation, the soft film moulds itself to the shape of the foodstuff to give a skin-tight package. This can give the food product an attractive appearance and better protection as no oxygen remains inside the package. VSP is used for some meat products and for fresh fish in some countries. MAP After having evacuated the air from the package, a modified atmosphere can be introduced before heat sealing the container. Thus, the packaged food will be surrounded by a gas mixture differing from the normal atmosphere. This is some times called gas flushing. The usual modified atmosphere is one without oxygen, simply because oxygen is involved in many quality degrading processes, see chapter 3 section 1. A number of combinations of nitrogen and carbon dioxide are used, for example 50% nitrogen and 50% carbon dioxide; the oxygen content must always be low, for some foods the oxygen content should be maintained below 0.5%. As plastic materials are not impermeable to gases, the composition of the gas mixture inside the package will change, albeit very slowly provided the packaging material has a very low permeability to oxygen and carbon dioxide, and the foods are stored at low temperatures. Therefore, this type of package should more correctly be called MAP (Modified Atmosphere Packaging) and not CAP (Controlled Atmosphere Packaging) as it is sometimes erroneously called . As mentioned in chapter 3 section 5.1 MAP with a rather higher oxygen content is sometimes used.

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It is comparatively easy to determine “leakers” in vacuum-packages (leakers are packages with a puncture or holes, so they can not maintain the “vacuum”) because the packaging material will no longer fit tightly around or be pressed against the foodstuff. When using MAP, it is much more difficult to detect “leakers” as the package will usually look the same whether it is intact or not. The only way to check is to analyze the composition of the atmosphere inside the package. This can be done by using a comparatively cheap and simple instrument. From records of the initial composition of the gas mixture, it can be calculated or judged whether the package in question has a sufficient degree of tightness. Masterpacks A special system, called Masterpack, is sometimes used, especially in the meat industry. The basic idea is that several consumer packs in conventional packages, such as overwrapped foodtainers, are placed in a large bag, which may be vacuumized or filled with a modified atmosphere. The bag is not opened until the retailer wants to display the consumer packs. If there is no oxygen in the master pack the meat inside the masterpack will change colour, but the normal bright red colour will reappear some minutes after exposure to normal atmosphere. CAPTECH This system was developed in New Zealand to help in transporting meat over long distances. The meat is packed in an “alufoil” laminate with a permeability to oxygen and carbon dioxide approaching zero. The air in the package is replaced by carbon dioxide, and the oxygen content in the package must be nil, or very low, throughout the life of the package. When the temperature in storage and transport is maintained at about -1.5°C

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PACKAGING

with a minimum of fluctuations, the storage life of lamb could be 20 weeks or more. The package can contain whole animals, wholesale cuts, or consumer packs. The system has been developed for container transport of chilled lamb from New Zealand to Europe, but could presumably be used for other types of meat. Thermoforming-Deep drawing Plastic materials become plastic when heated, and this is utilized in the manufacture of plastic packages. Thermoforming. Thick thermoplastic sheets or films can be formed into shaped containers by thermoforming. PS (Polystyrene), PVC and PA (nylon) are particularly amenable to this process. The plastic material is brought to plasticizing temperature by heating and the material is vacuum drawn or blown into the cavities of a mould. The sheet is thinned by this process and its permeability (barrier properties) may be reduced in inverse proportion to the square of the area increase. Thermoforming is used to produce semi rigid packages, e.g. trays for MAP meat. Deep drawing. Deep drawing is in principle the same as thermoforming, but deep drawing is carried out at the food producers packhouse. The packaging material is normally delivered in rolls. The food product is placed into the package immediately after the deep drawing process. The formed containers (trays) are lidded with a layer of packaging material from a second roll. The vacuum or MAP treatment can be performed at the same time as the heat sealing process. Deep drawing is used for many chilled and frozen products, especially in the meat industry. Many plastic materials used for deep

drawing will contain PA, as this material has good elasticity properties. PE will very often form the inner layer. Form-Fill-and-Seal Plastic pouches are often formed simultaneously with packaging the product. Preformed pouches are used, but most pouches are formed from plastic materials in rolls on two types of equipment: vertical and horizontal form, fill and seal machines. The packaging material may be a single layer of plastic, but often has a more complex structure, i.e. a laminate. Injection moulding Many rigid and semi rigid plastic packages (trays,boxes,etc.) are made by injection moulding. Blow moulding Plastic bottles and jars are normally made by blow moulding.

4.2 Outer packaging For most chilled and frozen food wrapped in inner packaging, an outer package is also used. As mentioned above, outer packaging is also called outer case, transport carton, transport packaging, etc. Proper transport packaging is essential to maintain product quality and to minimizing product losses during transportation and marketing. In addition, outer packaging serves to enclose the product and provides a means of handling. Poor quality packaging will lead to damage, lowering prices, or outright rejection of the often high value food products. The transport packaging must withstand: • Rough handling during loading and unloading.

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PACKAGING

Rough handling may occur in all parts of the chill/freezer chain, at the producing plant, in different storage rooms, during transport, and at its destination. The outer packaging must have sufficient strength to withstand these influences. • Compression from the overhead weight of other cartons Compression from outer packages stacked above can be severe in storage rooms, where stacking heights of up to 89 meters are sometimes used. However, outer packagings are normally not stacked so high, as racks etc. are used. During transport the maximum stacking height is about 2 meters. • Impact and vibration during transportation Impact and vibration during transport depends on the mode of transportation, for example road, rail or sea transport. • High humidity High humidity may be found in cooling down rooms, in most storage rooms, in transport equipment or during loading and unloading (if carried out unprotected from the weather). Many outer packagings are made of untreated paperboard, and the compression strength of such packagings can be reduced to less than half in conditions of 90% RH.

Outer packagings used include: • Paperboard cartons,boxes ( glued, interlocking, stapled ). • Plastic trays, boxes, film wraps, etc. • Foam boxes, trays • Wood bins, trays, crates,etc.

4.2.1 Paperboard Paperboard is the most widely used material for outer packagings. As mentioned above, the compression strength of un-

22

treated paperboard is reduced very much when water is taken up. Water take-up can be caused by condensation, for example when cartons containing deep frozen foods are placed in warm and humid surroundings for more than a short time. For outer cases where exposure to high humidity and/or water may occur, the paperboard must be wax-impregnated or coated with water resistant material, for example plastic. Glued cartons should be made using a water resistant adhesive. Paperboard is divided into several categories: • Containerboard. Containerboard is a general term used to include a variety of paperboards. Generally, it refers to solid fibreboard or corrugated board used in the manufacture of outer packaging and related products and their component materials, e.g. linerboard and corrugating medium (fluting). • Fibreboard. The term describes a material made primarily from wood fibres. It may be solid or corrugated and is used to make cartons and drums.

In most countries, solid fibreboard should have a minimum density of 1000 g/m2, while the board is between 250 and 1000 g/m2, and paper is up to 250 g/m2. 4.2.2 Corrugated board. Corrugated fibreboard, generally referred to as simply corrugated board, consists of a corrugated sheet of paper called the corrugating or fluting medium, faced on both sides with flat paper, called the linerboard or liner, see fig. 1.2. -Linerboard is a general term, often prefixed by a “quality” or grade description,

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PACKAGING

such as kraft liner (short for kraft linerboard), jute liner, test liner. Types of flutes. Several types of flutes have become standard: • A-flute is the thickest (4.6 mm), with the least number of flutes ( 110-120 per m ), and the greatest cushioning and shock absorbing properties.

properties. It offers greater stiffness, rigidity and crush resistance in the direction of its fibres, and an improved print reception surface for graphic design and point-of-sale impact. E-flute is widely used for liquor cartons, and for fragile foods that require both protection in transit and display/presentation provision. Normally, outer packaging is made with the flutes running vertically. In this direction they provide the greatest top-tobottom stacking strength.

• B-flute is 2.6 mm thick and has 160-170 flutes per m. • C-flute falls between A- and B-flute. • E-flute is 1.15-1.50 thick and has 250300 flutes per m. It has the highest flat crush and the least shock absorbing

Corrugated board construction. There are several forms of corrugated board. The name given to them varies from country to country and sometimes from region to region. Some important types are:

double-faced corrugated board; double lined; single wall; single flute corrugated board.

Double-double faced corrugated board; treble-lined; double wall; twin flute corrugated board.... Fig. 1.2 The two forms of corrugated board most commonly used for transport cartons.

In double-wall or triple-wall boards the flutes can be found in any combinations of the four flutes mentioned above.

weight per unit area. The weight of the most used material for packaging of foods is 250-400 g/m2

4.2.3 Boxboard Boxboard is a general term for grades of paperboard used for fabricating boxes. A measure and definition of grade is the

Folding boxboard is a paperboard made from a large variety of raw materials, suitable for the manufacture of folding cartons. The board must possess

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REFRIGERATION

strength qualities that allow creasing, folding, etc., and surface characteristics suitable for printing, etc. Special food boards are also a type of folding boxboards. This group generally comprises solid bleached cellulose boards. Food boards are frequently coated, with PE for example and after printing may be waxed. Examples are: frozen foods, ice cream and milk cartons. Frozen foods are sometimes wrapped in thin plastic before being placed in a carton. However, some frozen foods are marketed in a folding carton with no extra protection, but in these cases the foodstuff should not be susceptible to dehydration or oxidation. Some breaded products are packed in this way. 4.2.4 Types of cartons There are a number of different types of paperboard cartons, for example onepiece cartons, two-piece cartons with cover, two-piece carton with a full telescoping cover, self-locking trays, etc. Outer packaging for fresh fruit and vegetables should allow adequate air flow so that the commodities inside will maintain the desired temperature, see GUIDE TO FOOD TRANSPORT, FRUIT AND VEGETABLES. This is not necessary for the foods dealt with in this book, as these foods are “dead”, and therefore do not respire so do not produce heat as do fresh fruits and vegetables. However, for a few products the type of outer packaging with holes in the walls is used because the cooling takes place after the inner packages are placed in the outer package. The normal procedure for most perishable foods is that only products having the correct temperature are placed in outer cartons. In the retail trade, outer packaging will often be used for display purposes. Here,

24

a paperboard carton (perhaps after being opened to for a better display) or a paperboard flat with consumer packs overwrapped with plastic film is placed directly in the self-service shop.

5. REFRIGERATION During transportation, chilled and frozen foods preserve their quality if their optimum temperatures are maintained. This implies that the foodstuffs must be cooled to this temperature before being loaded into the transport vehicle, as refrigeration systems usually only have the capacity to cope with minor chilling tasks and to maintain product temperature. As mentioned later, this does not mean that the product temperature must be uniform throughout each piece of food. When the average (or equilibrium) temperature of the foods has been brought to the desired level, the transport can begin without quality problems, as the temperature will equalize without any need of further refrigeration.

If the commodities are highly perishable and, for some reason, have too high a temperature at the time of loading, they should be cooled as quickly as possible to avoid deterioration. When it is necessary to cool the food products during transport, the cargo must be stowed to allow the passage of air to all parts of the cargo. In all cases cooling by means of the refrigeration system in the transport vehicle will be a rather slow process which will reduce the quality and remaining storage life of the foodstuffs involved. The significance of refrigeration to a number of food groups is depicted in the relevant PSL diagram, see chapter 3 section 3,4 and 5. Here, the ideal and prescribed temperatures for each group of foodstuffs are also given.

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REGULATIONS

6. REGULATIONS In many countries, much legislation, with many regulations, directives etc. has been issued on foodstuffs, including the refrigerated transport of chilled and frozen foods. Specific regulations (legislation, standards, international agreements) on transport vehicles have been prepared, see section 6.1. For several chilled and frozen foods, and especially for meat and meat products, most countries have specific regulations on slaughtering, hygiene, temperatures, permitted additives, labelling, etc. The European Economic Community (EEC) now slowly evolving into a political union, so more correctly named the European Community (EC) have set up a number of regulations and directives concerning all aspects of the trade in foodstuffs. Some of the existing EEC-legislation today only applies for products marketed between the Member States and not for products marketed in the domestic market. Harmonization of the food law of the member states is still a matter of discussion and has not been obtained in all fields. For example the use of food additives, directive 89/107/EEC of 21. December 1988 on the approximation of the law of the Member States concerning food additives approved for the use in foodstuffs intended for human consumption, only contains a framework, but more specific regulations on permitted additives and the acceptable amounts are still to come. The EEC-legislation in the above mentioned areas is summarized in section 6.2, as is the legislation in a few selected countries. In section 6.3 the situation regarding legislation in the area of packaging materials is reviewed. Only a few countries have set up requirements for the materials used for packaging foodstuffs. The EEC has made a framework directive on

materials intended to come into contact with foods as well as a more specific directive relating to plastic materials. Irradiation of foodstuffs in order to reduce the number of micro-organisms and prolong the storage life is a matter of great international interest. Until now no international regulation applies, but both the Food and Agricultural Organisation (FAO) of the United Nations, the World Health Organisation (WHO) and the EEC are preparing guidelines/regulations in this area. A few specific countries have national legislation including the kind of foodstuffs to be irradiated and the acceptable doses. The situation regarding the use of irradiation is reviewed in section 6.4. With the intention of protecting the health of the consumer and to ensure fair practices in food trade, an international food standards programme has been established by the FAO and WHO. A short description of the work of the Codex Alimentarius Commission can be found in section 6.5. 6.1 Transport equipment Transport equipment should be built in compliance with relevant international standards, and tested to ensure that they conform. Transport equipment is classified on the basis of results obtained from these tests. Equipment for the carriage of perishable foodstuffs comprises wagons, lorries, trailers, semi-trailers, containers, and other similar equipment. International regulations have been established by the Economic Commission for Europe of the United Nations (ECE), the International Organization for Standardisation (ISO), and International Rail Union (UIC). ATP-Agreement The ECE Agreement on the International

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REGULATIONS

Carriage of Perishable Foodstuffs and on the Special Equipment to be used for such carriage (ATP) has been ratified by 24 countries: Austria, Belgium, Bulgaria, Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Ireland, Italy, Luxembourg, Morocco, Netherlands, Norway, Poland, Portugal, Spain, Sweden, Union of Soviet Socialist Republics, United Kingdom, United States of America, Yugoslavia. The ATP Agreement is the most important set of standards and regulations for the construction and use of insulated and refrigerated equipment. It occupies a place in road transport similar to that applicable to marine containers by the ISO regulations. The purpose of the agreement is to facilitate international traffic in certain perishable foodstuffs by setting common and centrally recognized standards. These standards should ensure that equipment is capable of maintaining the required product temperatures. ATP defines standards of insulation and refrigeration machinery as well as defining maximum temperatures for deep (quick) frozen, frozen and chilled foodstuffs, although it does not include fresh fruits and vegetables. The agreement requires the listed foodstuffs to be carried in equipment which has been certified by ATP, except where ambient temperatures render such equipment unnecessary. ATP does not apply to air transport, nor to sea voyages exceeding 150 km. Certificates of conformity to ATP are issued by officially designated test stations; today there are 18 test stations, most of them situated in Europe. These stations measure the K-value of the vehicle, and the performance of the refrigeration system.

26

K-coefficient. The K-coefficient (U-coefficient in some countries) or K-factor or K-value of the insulated body is a measure of the effectiveness of the insulation of the equipment. The K-coefficient (W/m2°C) is the overall coefficient of heat transfer, i.e. the heat transferred through the surface of the equipment. The International Institute of Refrigeration defines the K-coefficient as the heat transferred, in steady conditions, through unit area of surface, in unit time for unit temperature difference. The lower the K-coefficient, the better the insulation. The transport vehicle must have a Kvalue equal to or less than 0.4 W/m2°C to be classified as heavily insulated (IR), and a K-value equal to or less than 0.6 W/m2°C to be classified as normally insulated equipment (IN). A K-value of 0.2 W/m2°C or even lower is recommended in order to reduce the refrigeration load and reduce ageing of the insulation material. On average the Kvalue will increase by about 5% per year, due to water uptake and due to diffusion of freon from the insulation material into the atmosphere. Refrigeration system. The refrigeration system must be able to lower, and to maintain internal air temperatures according to the class of vehicle:20°C or below (classes C and F), -10°C or below (classes B and E), 0°C or below (classes A and D). ATP certificates. After inspection and measurement, the transport vehicle may be classified in one of the some 20 categories. A Type Approval Certificate is normally issued with a six-year validity. For other vehicles the certificate is normally valid for three

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REGULATIONS

years, after which a new inspection and/or new measurement must take place. Transport temperatures. The ATP-agreement, Annex 2, gives maximum permissible product temperatures during transport of frozen or deep frozen foods. Here it is stated that during certain operations, such as defrosting the evaporator of mechanically refrigerated equipment, a brief rise of the temperature of the surface of the foodstuffs of not more than 3°C in a part of the load, e.g. near the evaporator, above the appropriate temperature may be permitted. Annex 3 gives maximum product temperatures during transport of chilled foods (which does not include fresh fruits and vegetables). The temperatures given in annex 2 and annex 3 are included in this book, see the different groups of foodstuffs in chapter 3 section 3, 4 and 5. The ISO standard is a recommendation for performance and test of refrigerated containers. UIC is based upon ATP, and applies to railway wagons. There is very little difference between ATP and ISO or UIC. 6.2 EEC, and a few specific countries. Introduction. In order to obtain an Internal Market without barriers to trade within the Community, several directives have been issued to establish a common set of rules relating to the production, marketing and distribution of foods which would apply in all Member States. The EEC has sought to establish both horizontal measures which apply to a wide range of foods, for instance the directives on food labelling, and on materials in contact with foods-

and vertical measures which apply to specific food items, for instance directives on fresh meat, fresh poultry, minced meat, and meat products. It is recognized that it is impossible to make detailed technical standards for every foodstuff, and the future legislation is limited to consideration of public health, consumer information and fair trading. The following summarizes some of the above mentioned directives. However, many of the directives are being reviewed in 1990 and changes can be foreseen. No general international standards have been developed for the microbiological requirements for chilled or frozen meat products. This section includes a summary of the national requirements in this area in France, USA and Japan. Quick frozen food directive. In December 1988, a Council directive on quick-frozen (deep frozen) foods was issued (89/108/EEC). Quick-frozen foodstuffs are defined as foodstuffs which have undergone a suitable freezing process, whereby the resulting temperature of the food product (after thermal stabilization) is maintained at -18°C or colder at all points. Also, the foodstuffs must be marketed in such a way as to indicate that they possess this characteristic. Article 5 states that the temperature of quick-frozen foodstuffs must be -18°C or lower, with possible brief upward fluctuations to -15°C during transport. However, tolerances in the product temperature in accordance with good storage and distribution practice shall be permitted, up to -15°C during local distribution (in some

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REGULATIONS

EEC countries the limit may be -12°C until 1994), and up to -12°C in retail cabinets. For retail cabinets, some countries may prescribe colder maximum product temperatures. Article 11 states that a directive on sampling procedures for quick-frozen foodstuffs and the procedures for monitoring their temperature must be issued in 1990. In this directive it will probably be prescribed that the means of storage, warehousing and transport must be fitted with suitable recording devices to automatically and constantly monitor the air temperatures to which quick-frozen foodstuffs are subjected. The temperature recordings obtained in this manner must be dated and stored for a certain period. For retail display cabinets and for local distribution, temperature recording devices will not be mandatory. Here the temperature must be monitored by at least one thermometer. Food labelling directive. EEC directive 79/112/EEC on labelling, presentation and advertising of foodstuffs has been developed in order to provide the consumers in the EEC with relevant information on the foodstuffs concerned. By the latest amendments of this directive (89/395/EEC), the application field is prepackaged food products for sale to the ultimate consumer and for catering purposes. The labelling must include the following information: The name under which the product is sold, • the list of ingredients, • the net quantity, • the date of minimum durability, or - for foodstuffs which are microbiologically highly perishable -

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• a “use by” date, • any special storage conditions or conditions of use, • the name or business name and address of the manufacturer or packager or of a seller established within the Community.

Furthermore, the directive includes specifications on how the above mentioned information should be presented on the label. It is stated that it is prohibited to provide information on the label or in the presentation and advertising of the foodstuff which could mislead or confuse the consumer. The directive on food labelling is supplemented by a directive on indications or marks identifying the lot to which a foodstuff belongs (89/396/EEC). This identification should be preceeded by the letter “L” and could be excluded if the date of minimum durability or the “use by” date is given in the label and at least includes a statement of day and month. Fresh meat directive The trade in fresh meat within the EEC shall comply with the regulations in the Directive 64/433/EEC relating to health problems affecting intra-Community trade in fresh meat (with further amendments). Fresh meat must have undergone a thorough veterinary health inspection outlined in the directive and shall be stamped with a health mark before being dispatched. The meat shall be followed by a health certificate. The directive includes the conditions for the approval of slaughterhouses and cutting plants, and detailed requirements for the hygiene of slaughter and cutting as well as for the persons engaged in the handling of the meat. Also mentioned are certain requirements for the storage and transportation of the fresh meat.

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REGULATIONS

Without undue delay, the meat must be chilled to an internal temperature of 7°C or colder for carcases, half carcases, half carcases cut into three wholesale cuts, and quarter carcases, and 3°C or colder for offal. The meat should be kept constantly at or below that temperature. Fresh meat intended for freezing must be frozen by a rapid method and be stored at -12°C or colder. These temperatures should be kept throughout the period of transportation. Poultry meat directive The trade in fresh poultry and poultry meat within the EEC must be in accordance with the Directive 71/118/EEC relating to health problems affecting trade in fresh poultry meat (with further amendments). The directive lays down detailed requirements to the slaughterhouses and the veterinary health inspection as well as provisions for health marking. The internal temperature of the fresh poultry should be 4°C or below, and this temperature should be kept during transportation. For poultry marketed within the Community, a Commission Regulation (EEC) No. 2967/76 lays down common standards for the water content of frozen and deep frozen chickens, hens and cocks. Poultry can only be marketed if the water content does not exceed the technically unavoidable minimum absorbed from the chilling processes stated in the Regulation as determined by further specified methods of analysis. If the amount of water absorbed is greater than the specified level, an appropriate description should be attached before the poultry is marketed. Minced meat directive EEC Directive 88/657/EEC on minced meat and pieces of meat less than 100 g

establishes requirements for the production and trade in the EEC of the type of meats. If the meat is sold chilled in retail packages, it must be prepared at latest 6 days after slaughter of the animal. The temperature should be below 2°C. If the processing of the meat takes a maximum of 1 hour, the temperature in the centre of the meat must not exceed 7°C, and the temperature in the production rooms should be 12°C or colder. If the processing takes more than 1 hour, the centre temperature of the meat must be a maximum 4°C before processing. Immediately after processing, the meat must be hygienically packaged and stored at 2°C or colder in the case of chilled meat, at -18°C or colder in the case of deep frozen meat and at -12°C or colder in the case of frozen meat. Deep frozen minced meat or packages of pieces of meat less than 100 g should reach a temperature in the centre of the product of -18°C or colder within 4 hours. Frozen products should reach a temperature of -12°C in the centre within 12 hours. However, the latter products must not be retail packaged. Intra-community trade of minced poultry meat, minced meat containing mechanically recovered meat or offal or minced meat from hoofed mammals is accepted only into Member States which on their own territory allow production and sale thereof. If spices are added to the minced meat, the acceptable amount of spices is 3% of the finished product when the spices are dry if mixed with the meat, and 10% when mixed in any other condition. Meat preparations made from minced meat mixed with other ingredients, e.g. spices, additives and flour, can be dispatched only on the condition that they are frozen at a freezing speed of at least one cm/hour.

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These meat preparations must be marketed within 6 months of production. The directive sets up compositional stan-

dards for different types of minced meat regarding the fat content and the collagen/meat protein ratio:

Fat Content

Collagen: Meat Protein Ratio

Lean minced meat

≤7%

≤12%

Minced pure beef

≤20%

≤15%

Minced meat containing pig meat

≤30%

≤18%

Minced meat of other species

≤25%

≤15%

The products must comply with the following microbiological standards: M

m

Aerobic mesophile bacteria n=5; c=2

3x106/g

5x105/g

Escherichia coli n=5; c=2

5x102/g

50/g

102/g

10/g

5x102/g

50/g

Sulphite-reducing anaerobes n=5; c=1 Staphylococci n=5; c=1 Salmonella n=5; c=0

absence in 25g

M = acceptability threshold, above which results are no longer considered satisfactory m = threshold below which all results are considered satisfactory n = number of units making up the sample c = number of units in the sample giving value between m and M

The directive includes specified interpretations of the results of the microbiological analyses.

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Meat products directive. The EEC directive 88/658/EEC of 14.December 1988, amending directive

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77/99/EEC on health problems affecting intra-Community trade in meat products harmonized the regulation in this area. This directive defines meat products as products prepared from or with meat which has undergone a treatment such that the cut surface shows that the product no longer has the characteristics of fresh meat. Processed poultry products are included in this directive. Excluded from the field of application are meat extracts, meat consomme’ and stock, meat sauces, and a number of by-products e.g. animal gelatin and blood plasma. The treatments can be heating, salting, curing or drying, or a combination of these processes.

permissible percentages from a technological viewpoint should be taken before 1 January 1991. Several of the Member States have their own regulation on meat products, not only for the incorporation of the above mentioned substances but also requirements to the minimum meat content, maximum water content etc. Until further notice these regulations still apply for the products marketed in the domestic market. A crucial principle of the EEC is that products legally produced in one Member State shall be allowed free entrance to any other Member State provided that they do not constitute any health hazard.

The directive includes conditions for the approval of establishments and for hygiene. The production must be supervised by competent authorities, the products must carry a health mark and must be accompanied by a health certificate. For meat products in general, neither compositional nor microbiological standards have been set up in the Community. Article 15 states however, that a decision on the incorporation into meat products of starch or proteins of animal or vegetable origin and on the maximum

Other Standards for Meat and Meat Products For chilled or frozen meat and meat products in general, no general international microbiological standard apply. However, several countries have set up national standards for these products. In France, detailed requirements for the microbiological standard of meat products are set up. The acceptable number of micro-organisms per gram for selected types of meat can be seen in the following table.

Aerobic Coliform, Coliform, micro30°C faecal organisms Carcasses, frozen or chilled

5x102

Minced meat

5x105

Cooked meat products

3x103

Poultry, whole, frozen or chilled

Staph. aureus

Anaerobic, Salmosulphitenella reducing 2

102

102

102

30

absent

10

102

30

absent

absent in 25g breast muscle

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The US Meat and Poultry Inspection Regulations imposes requirements for meat inspection as well as standards of composition for a number of meat products. The minimum meat content for some of the products are specified and the use of certain ingredients is restricted. Japan has set up standards for the manufacture of meat products but does not have specified compositional standards. Sugar, starch and seasoning used in manufacture must have not more than 1000 heat resistant bacteria (spore forming count) per g. Products must be sterilized to a centre temperature of 63°C for 30 min. (or equal) unless they are dried. Dried and smoked cured meat must be prepared at temperatures below 20°C or above 50°C, and the product must obtain a water activiy less than 0.94. Meat products not being sterilized in airtight packages must be stored at a temperature below 10°C (frozen products must be stored at -15°C or colder). 6.3 Packaging regulations. In many countries, the legislation on packaging materials (and especially on plastic materials) is not very comprehensive. Several countries have realized that the area of plastic packaging is changing so rapidly, that it is very difficult for the legislators to remain up to date. However, some countries have had detailed regulations on packaging materials (and other materials intended to come into contact with foodstuffs) for many years. In this section, the regulations in USA, West Germany and EEC will be summarized. USA. Packaging was brought into the Food, Drug and Cosmetic Act by an amendment issued in 1958. The use of plastics and other packaging materials in contact with

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food is under the direct jurisdiction of the Food and Drug Administration (FDA) who issues detailed positive lists for permitted plastics and additives. The FDA regulations are held in great respect throughout the world. Many countries tend to follow them, often in a simplified form. The Governmental Regulations cover all chemical components of the food supply in the USA, whether these components enter the food by direct addition or by indirect means, for example, by virtue of migration from a food packaging material. Thus, there is a great deal of work in bringing under control, by scientific evaluation, the many thousands of substances involved in foods and in food packaging materials. All packaging materials and the additives used must comply with the FDA regulations, which in a number of sections include positive lists for food packaging materials, i.e. lists of approved plastics and additives with maximum concentrations, all others being banned. The user of packaging materials has to obtain assurance from a particular supplier that the material in question actually meets with provisions of a specific regulation. Migration. Migration of additives from the packaging material into the foodstuff is one of the areas where comprehensive tests are run. Migration tests normally utilize a range of solvent solutions capable of simulating food extraction, for example distilled water, 3% water, 3% aqueous acetic acid, and vegetable oil. USDA. The Department of Agriculture issues reg-

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ulations on packaging, especially concerning the packaging of meat and poultry products. In order to import such products to the USA, it is necessary to obtain a written concession, which includes the packaging material that is to be used. West Germany The Ministry of Health (Bundes Gesundheits Amt) has issued comprehensive guidelines for packaging materials, the so-called BGA-rules. This is not legislation, but if a packaging material does not conform to the BGA guidelines, the guidelines are treated as if they were legislation, and the company (or person) can be prosecuted. BGA guidelines include positive lists, i.e. lists including the components permitted in the manufacture of food packages, and the allowed maximum amount of each of these components. The guidelines also contain limits for the permissible migration from the packaging material, and from the packages in contact with food. EEC. Some years ago, the EEC Council issued a framework directive on materials and articles intended to come into contact with food. Based on this, some directives have been issued, for example a Directive on PVC, which limits the quantity of vinyl chloride (VCM=Vinyl Chloride Monomer) present in plastic materials prepared with VCM, and for the quantity of VCM released by these materials, i.e. a specific migration limit for VCM. The compilation of positive lists for plastic materials has been in preparation for several years, as it was a difficult task to harmonize the existing legislation in

the 12 Member States. However, Directive 90/128/EEC relating to plastic materials and articles intended to come into contact with foodstuffs was issued in February 1990. The Member States must bring into force the laws, regulations and administrative provisions necessary not later than 31 December 1990, and prohibit trade in and use of plastic materials which do not comply with this Directive before 1 January 1993. Only those monomers and other starting substances listed in Annex II of this directive may be used for the manufacture of plastic materials and articles. The directive also limits the overall migration from plastic materials into foodstuffs: The overall migration limit is 10 milligram per square decimeter of surface area of plastic material (mg/dm2), or 60 mg per kilogram of foodstuff (mg/kg). The positive lists in Annex II includes specific migration limits (in mg/kg foodstuff) for several substances. Earlier EEC Directives have laid down the basic rules (time, temperature, etc.) for testing migration of the constituents of plastic materials, and have established the list of simulants to be used in the migration tests. The simulants prescribed are approximately the same as in the USA regulations, see above. As mentioned in the introduction, several countries do not have detailed legislation on food packaging. A few countries have recommendations, while some countries simply refer to the legislation in other countries. This means that the authorities in several countries simply demand certificates that the packaging materials comply with the legislation in West Germany (BGA), or USA (FDA) or the Netherlands. The regulations on packaging materials to be used for foodstuffs is an important

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area as the authorities in several countries demand certification that imported foods are packed in suitable and safe packagings. 6.4 Irradiation The use of ionizing radiation of foods is a topic of great interest world-wide. There is no international legislation in this field, but FAO/WHO have drawn up a proposal for international standards. A FAO/WHO expert group has concluded that irradiation of foodstuffs is a completely safe method, when the dose absorbed by the foodstuff is below a certain limit, 10 kGy (1 Mrad). Several countries have appointed expert groups with the task to study irradiation of foodstuffs, but all of them have supported this conclusion. Irradiation may be used for several purposes: • to retard sprouting of potatoes and onions. This demands a dose of about 0.2 kGy • to kill insects in for example wheat. This demands about 0.7 kGy • to kill bacteria and micro-organisms, in order to prolong storage life of for example fresh (chilled) strawberries, or to significantly reduce (eliminate) the number of food poisoning micro-organisms, such as Salmonella and Campylobacter, see chapter 3 section 1.1. The dose normally is 3 to 7 kGy. • to kill micro-organisms in spices and herbs in order to increase the safety and storage life of the foods to which these spices and herbs are added. The necessary dose is 10 kGy. • in order to produce ambient stable food

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products, i.e. food products stable for some months at room temperature (20°C) it would be necessary to use a dose of about 45 kGy. As this is above the maximum permitted dose of 10 kGy, shelf stable irradiated foods will not be seen in the trade.

This implies that even when irradiation becomes a permitted method the irradiated food products would still need cooling and temperature controlled transport. The temperature requirements and the monitoring of product temperatures during transport (and during storage and display) would probably be intensified for irradiated foods. There is no advantage for the food industry in using as high a dose as allowed in legislation, because irradiation may cause pronounced changes, especially in flavour and taste. The maximum dose to be used in practice will differ, from about 10 Kgy for killing most micro-organisms in spices, to 3-6 kGy for killing of pathogenic microorganisms (Salmonella, Campylobacter), down to 0.1-0.2 for potatoes. In several foods, for example in many dairy products, significant flavour changes occur when the dose exceeds 0.5 kGy, meaning that irradiation can not be used commercially for such foods. However, although (or perhaps because) practically all experts agree that irradiation could be a very useful preservation method for some foods, most consumer organizations and media persons seem to be convinced that irradiation is a very dangerous, or at least unwanted or unnecessary method. In the EEC, a draft Directive on irradiation is being discussed in 1990. The draft includes a list of food groups with the proposed maximum allowable dose for each group. Irradiation of foodstuff, especially of

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spices, is employed in several countries, such as USA, Netherlands and Japan, but only to a very limited extent. Irradiation is permitted in many countries, but is often not applied in practice because of labelling regulations and public opinion, which means that food producers and retailers reject using this theoretically excellent method. It may be added that labelling of irradiated foods and ingredients is a crucial factor. If the industry was allowed to irradiate some foods without having to state “irradiated” or “ionized radiation” on the label, it might be a lot busier irradiating food, especially spices, rather than confined to sterilizing medical utensils, petri dishes, and the like. 6.5 Codex Alimentarius The international organizations FAO and WHO established, in 1962, the Codex Alimentarius Commission to implement a joint food standards programme. The purpose of the programme is to protect the health of the consumers and to ensure fair practices in food trade both nationally and internationally. In pursuit of these objectives, efforts have been put into the standardization of several types of product categories as well as standardization of labelling, use of additives, food hygiene, pesticide residues, etc. Furthere, recommended international codes of hygiene and/or technological practice have been developed, for example in the fields of fish and fishery products, meat and poultry products, fruits and vegetables. Foodstuffs complying with the Codex can generally be considered as being safe, wholesome and good quality. As of 1989, 137 countries had become members of the Commission.

The published work of the Commission can be found in the Codex Alimentarius which consist of Standards (at present in 17 volumes), recommended Codes of Practice and Guidelines (at present in 8 volumes) and regularly up-dated tables of government replies. It should be noted that the Codex Alimentarius is advisory only, but that it can be valuable in the communication between buyer and seller. Food Labelling Codex standards and Guidelines for the labelling of foods and food additives (CAC/Vol. VI-Ed.2) include a standard for the labelling of prepackaged foods. The standard supplies the points of interest for all consumers and the requirements can be observed in practice. Countries often base their food labelling law on this standard which has also influenced the regulation in this field in the EEC. Standards The programme has set up Codex standards for various foods, e.g. for processed meat and poultry products (CAC/vol. IV - Ed. 1). These standards, mainly dealing with composition and labelling of certain specified meat and poultry products, applies only to canned products. However, a recommended code of hygienic practice for processed meat products has been made especially concerning requirements for the ingredients used, and the facilities in the factories. The end product specification states that the product should not contain pathogenic micro-organisms in amounts that would constitute a health hazard to the public without establishing limits to the actual numbers. For fish and fishery products (CAC/Vol. V - Ed. 1), standards have been developed

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for some canned products as well as some quick frozen fish species (e.g. Pacific Salmon, Cod, Haddock, Flat Fish, Shrimps). These standards include lists of defects in the fish products which can be used in quality evaluation. For certain quick frozen fruits and vegetable the standards also include defect “lists” (CAC/Vol. VIII - Ed. 1). 6.6 Other regulations It should be noted that besides all the topics dealt with in this section, there are many other special regulations throughout the world. The use of chlorine in the washing and chilling of chickens is recommended in certain countries, but forbidden in others. Some additives are considered useful in some countries, but are forbidden in neighbouring countries. The application of colouring to fresh fruits and vegetables is allowed in some countries, such as Japan, but there are no international regulations or outlines on this matter. It is appropriate, therefore, to refer to the particular country’s regulations in each case.

Such a procedure would only indicate the temperature at that moment in time, and give no indication of the time- temperature history of the load, which may be important for the quality of the foods, and for the safety of chilled foods. Checking temperatures in transported cargoes is straightforward, provided certain procedures are followed. Transport vehicles in themselves are relatively simple however, the refrigeration system as a whole is complex and it’s temperatures are neither uniform in distribution nor constant in time. It is recommended to use the following sequence of inspections and measurements in checking temperatures in transport of chilled and frozen foods: a. - Inspection and checking a log or a record of air temperature measurements. In most cases, further action will be superfluous. b. - Use of a non-destructive product tem-

7. TEMPERATURE MONITORING AND TEMPERATURE MEASUREMENT This looks at what methods should be used in checking that the food in the vehicle or container has been maintained at the prescribed temperature.

It is in the interest of all parties that there is minimal disruption during the journey of perishable produce, especially at border crossings. Any manual temperature measurement carried out by inspection authorities will require the vehicle to be opened, temperature measuring devices inserted, etc.

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Fig. 1.3 Vehicle seen from behind, indicating the position of product temperature (by a non-destructive method) in transit or before unloading

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perature measurement, should the air temperature measurements leave reasonable doubt about the temperature of the food products. c. - Use of a destructive temperature measurement method. This stage should only be undertaken, where the evidence from stages a and b lead to the conclusion that the food could be outside the required temperature limits.

7.1 Air temperature measurement. Suitable air temperature recorders should be installed in all types of transport equipment for long-distance transport of perishable foods. At the receiver, the air temperature record should be examined. Verification of the position and accuracy of the sensors is difficult in a loaded vehicle. It may be possible to check the accuracy of a sensor situated near the rear of the vehicle. The readout of this sensor and a calibrated control instrument should be the same. As mentioned above, the temperature check will normally end at this point.

However, if air temperature data are not available, or the air temperature record is not satisfactory, then the product temperature should be measured by a non-destructive method, (the between pack method, see section 7.2.1). A number of companies have specific guidelines on testing temperatures of incoming foods. When a transport vehicle arrives, inspectors test temperatures, and the guidelines for such temperature tests may include one or more measurement. It seems that more and more companies carry out quality control, including temperature measurements, of practically all foods received, whether chilled or frozen, whether raw materials or finished products. Such procedures should be considered an advantage for all parties involved. 7.2 Product temperature measurement Product temperatures may be checked whilst the vehicle is still loaded, but inspection should not cause rises in load temperature, and only those packs available from the doors should be examined. When it is considered necessary to check

Fig. 1.4 Vehicle with a single set of doors. It is indicated (x) where product temperatures should be measured, preferably using a nondestructive method.

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product temperatures during transport or before unloading, it is recommended to take a measurement at the position shown in figure 1.3, but the exact position may depend on type of packaging and stowage. It is recommended to begin with a non-destructive product temperature measurement, see section 7.2.1. If further investigation is required, then unloading should take place and measurement be conducted under controlled conditions, i.e. the load should be placed in a room having about the same temperature as the foods. Unloading of the vehicle should be carried out so that the products to be measured can be identified or marked for measurement under temperature controlled conditions. For vehicles with a single set of doors, the product temperature should be measured at six points, as shown in figure 1.4: • At the centre of each doorway, at the top and bottom • At 1/4 and 3/4 the distance from rear and front, at the centre of the load • At half the distance from the rear, at the top of the load • At the front, one sample from the bottom centre position

For vehicles with more than one set of doors, a more complicated sampling plan is necessary. In all cases, product temperatures should be determined using the non-destructive method. If between pack temperatures are too high, the packs should be set aside for

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destructive measurement (section 7.2.2, below), which should be carried out with the minimum of delay. 7.2.1 Non-destructive measurement If the top of a case is accessible, it should be opened, and the sensor inserted between the food packs. If not, a small flap should be cut at the edge of the outer case, taking great care not to damage the food packs, see figure 1.5. A sensor can be placed between food packs, which should be under sufficient pressure to give a good contact, and the temperature read after reaching a steady value. Between pack measurements can give rise to a 2°C difference between measured and true product temperature. 7.2.2 Destructive measurement As mentioned above, the destructive measurement should not be used until the non-destructive measurements have lead to the conclusion that the food may be too warm. For frozen foods, it is necessary to precool the temperature sensors, and for solid food products it is necessary to make a hole of the appropriate diameter, using a pre-cooled punch or drill. The drilling or formation of a hole generates heat. This can cause large errors in reading the true temperature, especially in foods having a low capacity to absorb heat. This is particularly true of small consumer packs. For chilled foods there is normally no need for pre-cooling the temperature sensor or taking other elaborate precautions. The measurement should be made whilst the food remains in chilled/frozen surroundings, and the temperature measured at least 25 mm below the surface (or in the centre when the product is less

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Fold back

Cuts made with a sharp knife

Temperature sensor

Fig. 1.5 Illustration of non-destructive (between pack) temperature measurement

than 50 mm thick). The temperature should be recorded after reaching a steady value. The sensor should remain in the test package until it is required for the next measurement. 7.3 Temperature recording during transport As mentioned before it is highly recommended - and in the EEC countries mandatory for long distance transport of deep frozen foods and for transport of some chilled foods- to install a suitable temperature recorder in the transport equipment. Temperature recorders are dealt with in chapter 2 section 3.4 7.4 Temperature measuring instruments Temperature measuring instruments should meet the following requirements: • stable temperature reading should be achieved within 2 minutes. • the instrument should give readings to an accuracy of +/-0.5°C or better in the temperature range -20°C to +20°C. • the accuracy of the instrument should not

be affected by the temperature of the surroundings, between the temperatures 20°C and +40°C. • the markings on a scale should be readable to 0.5°C, or a digital readout of the same order or better. • the temperature sensitive element should be enclosed or constructed from materials that are non-toxic and capable of being sterilised. • the temperature sensitive part of the instrument should be constructed to facilitate good thermal contact with the food product.

The instrument used should be powered by a dry cell battery and incorporate a method of checking the battery voltage to indicate when replacement or recharging is necessary. The read-out may be digital or dial display. The temperature sensor should be built into and form either a robust rigid stem with a sharpened point suitable for insertion directly into the product or into a predrilled hole or be formed into a flat head

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TEMPERATURE MONITORING AND MEASUREMENT

suitable for measurement of surface temperature on or between packages. Calibration of instruments The temperature measuring instrument should be tested at regular intervals. Instruments may be checked by comparison to a readings with a reference thermometer known to be accurate.

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Modern electronic instruments often have their calibration “factory set”. Therefore if and when comparing with a reference temperature the difference is greater than 0.5°C, the thermometer should be sent back to the manufacturer for re-calibration. On older models adjustments can be made until the readings are within that value, but the instrument should be rechecked after adjustment.

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2 CHAPTER

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GENERAL INFORMATION ON TRANSPORT

TRANSPORT CONDITIONS Chapter 2 deals with the transport equipment used in the transport of chilled and frozen foods. Section 1:

General information on transport. Heat sources, insulation, temperature requirements, pre-cooling, loading/ unloading, mixed loads.

Section 2:

Mechanical refrigeration. Principle, mechanical refrigeration units, thermostats, defrosting.

Section 3:

ISO intermodal containers, including air ventilation, controllers, temperature recording, loading.

Section 4:

Primary distribution vehicles (trailers, trunkers).

Section 5:

Other types of refrigeration systems

Section 6:

Other types of transport equipment.

Section 7:

Code of good practice for refrigerated transport. Before loading, unloading, pre-cooling of foodstuffs.

1.GENERAL INFORMATION ON TRANSPORT. The transport of chilled and frozen foods

can involve movement by road, rail, sea or air or combinations thereof, employing thermally insulated vehicles or containers which are normally equipped with a refrigeration system for maintaining the desired temperature in the cargo space. The mode of transportation and type of equipment used should be based on • destination • outside temperature conditions during transport • amount and value of the product • recommended temperature during transport • time in transit to reach destination • product perishability The following transport equipment is available: • ISO containers • Primary distribution vehicles (trunkers, trailers) • Secondary distribution vehicles • Piggyback trailers, for rail,road and rollon/roll-off sea transport. • rail cars • ocean vessels, with refrigerated holds. • air cargo containers

This book concentrates on long distance transport, and in this chapter mainly ISO containers (section 3) and primary transport vehicles (section 4) will be described. A few other types of transport equipment will be described in section 6.

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Long distance transport require welldesigned equipment, and desirable features include: • sufficient refrigeration capacity • a continuously operating high capacity evaporator air circulating fan for more even product temperatures • adequate insulation • adequate air circulation under the load • containers: delivery air temperature sensors are used for chilled foods in order to reduce freezing injury • containers: return air sensors are always used for the transportation of deep frozen (and frozen) foods • trailers: inlet air ducts to ensure even air distribution • trailers: provisions, e.g. a solid return air bulkhead, at the front to ensure air circulation • trailers: vertical ribs on the rear door to assist in air circulation 1.1 Heat sources The refrigeration system in transport equipment must have sufficient capacity to remove heat from the following sources: • heat conducted through the insulation from warm outside air • heat absorbed from radiation from the sun or the road • infiltration of heat from warm outside air through small holes and cracks • heat from the evaporator fan and motor • heat from any internal electric lights, if fitted • heat introduced through open doors (very important in local distribution) • residual heat from the air inside the cargo space, and residual heat in the insulation and inner lining • foodstuffs with a temperature above the required temperature • heat of respiration is not relevant for the foodstuffs dealt with in this book. The refrigeration system must have suffi-

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cient refrigeration capacity to remove the sum of these sources. This should be done in such a way as to minimise the temperature difference of the air passing over the evaporator coil so as to avoid the dehydration effect caused be water condensing from the circulating air, see section 2.4 below. It must be emphasized that the foodstuffs must have the desired temperature when loaded into the transport equipment. If the foodstuffs are at a higher temperature, they must be cooled to the desired transit temperature before loading. 1.2 Insulation Transport equipment to be used for transporting perishable foods, should be well insulated to retard the flow of heat through its walls. Insulating quality is measurable, and the commonly used unit of measure is the K-coefficient (K-factor, K-value), see section 6.1 in chapter 1. To obtain an ATP certificate for international transport of frozen and deep frozen perishable foodstuffs, the K-value for heavily insulated equipment must be 0.4 w/m2xC or less. The lower the K-value, the better the insulation. Plastic foams, and especially polyurethane foam, are the predominant materials used in insulated refrigerated equipment. Polyurethane foam almost always incorporates a low conductivity halocarbon gas within closed cells to improve the performance. The insulation thickness was usually about 70-80 mm for the side walls and about 100 mm for roof and floor. Due to improvements in polyurethane insulation technology, side walls with a thickness of about 60 mm are now being used by some manufacturers. Plastic foams give a low K-value, are lightweight, waterproof, and noncorrosive.

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In 1989 the EEC decided to increase the maximum external width of road vehicles in ATP class FRC, i.e. vehicles capable of maintaining -20°C. For such vehicles, the maximum permissible width was changed from 2500 mm to 2600 mm. With a maximum width of 2500 mm, thin wall vehicles were used to some extent, see section 6.3 below.

temperature may accelerate water loss and can cause frost formation inside retail packed deep frozen foods such as vegetables, meat balls, see chapter 1 section 3.2. The ideal and the prescribed transport temperatures for some groups of deep frozen, frozen and chilled foods can be found in chapter 3 sections 3, 4 and 5.

Most new vehicles have bodies constructed of sandwich panels, with plastic foam laminated between fibreglass or stainless steel or aluminium walls. Sandwich panels give a low K-value, even at reduced wall thickness.

Chilled foods. Generally, the temperature should be as cold as possible. This very often means that the temperature should be maintained a little above the freezing point of the foodstuff, for example 0.5°C,. As mentioned in chapter 1, the freezing point for most raw foods is about -1°C to -2°C. Thus, the ideal transport temperature for such chilled foods is -1°C with a minimum of fluctuations. As stressed below, it is not possible to maintain constant temperatures in transport equipment. If the controller in a container is set at 0°C, the delivery air temperature will be around 0°C. The return air will be warmer, e.g. 1-2°C, and the average temperature of the load will be 0.5-1°C.

The outer cladding should reflect heat radiation; reflective paints could also reduce the heat load. However, the reflecting effect is reduced if the outside of the vehicle is not kept clean. As mentioned later, polished metal (stainless steel or aluminium) is normally used for the outside skin on ISO containers. Insulation materials of high quality are of little value if door seals etc. are leaking. The door seals must be kept properly fitted and in good repair. Polyurethane foam deteriorates with age, partly due to loss of halocarbon, partly due to moisture ingress. The overall range of rate of deterioration is about 5% per year, somewhat lower for some of the newer sandwich panels. 1.3 Temperature requirements With perishable products of all types temperature is of prime importance, i.e. the food products must maintain low temperatures throughout the cold chain. In transportation of chilled foods freezing injury must not occur, i.e. it is often necessary to ensure that the circulating air does not become colder than about -1°C. Also, the air temperature must be as constant as is practicable, as fluctuating air

Frozen foods The quality is maintained best when the temperature is as low and constant as practicable. In freezer storage rooms the temperature is very often about -28°C, and in transport the temperature is normally -18 to -25°C. Air circulation Regardless of the method of refrigeration, provision should be made for the conditioned air to circulate uniformly. In warm weather, the primary purpose of air circulation is to carry heat penetrating walls, floor and ceiling of the transport equipment to the refrigeration unit which removes the heat. Circulating air, like water, tends to take the path of least resistance

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or short-circuit back to the refrigeration unit. The cargo must be uniformly stowed to achieve uniform air passages, necessary to obtain uniform product temperatures. 1.4 Pre-cooling Transport equipment is designed to hold the product at a desired temperature. Containers or trailers rarely have sufficient refrigeration power to reduce the temperature of the mass of the cargo to the required level as quickly as is normally required. The foodstuffs must have the correct temperature when loaded. For further information on pre-cooling of foodstuffs, see section 7.4 below. Pre-cooling the transport equipment As the outside temperatures, refrigeration unit capacities, and insulation (K- values) all vary, there can be no set rule for precooling of the transport equipment. In most cases, there is no need to precool the equipment before loading as the heat from the equipment will warm the cartons against the walls by only about 0.5°C. In several countries, a recommended procedure before loading is to set the thermostat at the desired temperature, close the doors, and run the refrigeration unit for about half an hour. This is especially recommended for deep frozen foodstuffs. Some countries prescribe pre-cooling, i.e. it is mandatory to pre-cool the transport equipment before loading. It is obvious that ambient air should not be allowed to pass into pre-cooled trailers or containers, as this would cause condensation. 1.5 Loading The most important factors to take into consideration during the loading process are time and contact with ambient air.

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Ideally, the loading bay should be kept at the same temperature as the required carriage temperature. In that case, the trailer/container should be connected to the cold room or the loading area via a port door with seals. This is not always the case, but vehicles should at least be placed so the loading doors are under cover away from direct sunlight. Because of restriction in space, before vehicles are backed into loading bays the hinged doors must be opened and folded back. If delays in loading occur and the bay is not temperature controlled, then undesirable large temperature rises can occur. Perishable foodstuffs must not be allowed to remain outside the cold room unnecessarily while waiting to be loaded into the transport equipment. If a pallet load of deep frozen foods with a temperature of -25°C is placed at +15°C, the temperature of the foods placed in the outer corners will be about 12-15°C warmer, i.e. about -10°C, after a period of 2 hours. After 4 hours at +15°C, the corner temperatures will be around -5°C, while the foodstuffs in the centre of the pallet will still be colder than -20°C. Of course, if the ambient temperature is warmer than 15°C and/or the pallet is left in the sun unprotected, the increase in temperature of the foodstuffs will be much more pronounced. Loading patterns Packaging and packaging materials are described in chapter 1 section 4. It is self-evident that whatever packaging is used, it must be secure. What is important is that while remaining secure, the packaging must allow air to circulate freely around the periphery of the container and in the area of the door. The important criterion here is to have uniform distribution of air throughout the load.

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This requires the cargo to be uniformly stowed. Different sized packaging obviously dictates different stacking patterns. The higher the resistance to the air pressure developed by the fans, the smaller the volume of air that will pass over the cargo and, subsequently, the lower the rate of heat exchanged between the air and the cargo. In an extreme case, the high resistance to air flow will mean that cargo will have relatively little or no air flowing over it. Conversely, in cargo stowed with large gaps and no resistance, the air will short-circuit through the low-resistance areas and return to the refrigeration unit without cooling the bulk of the cargo. As stated earlier, the key to uniform cooling is uniform air distribution. For the foods touched on in this book, the transport cartons should be loaded in a solid block. The goal is to keep the heat that penetrates the vehicle from reaching the cargo by keeping the load encircled with an envelope of cold air. The internal dimensions of containers/ trailers differ considerably, and carton sizes also differ. Thus, it is not possible to specify one standard stowage pattern. Most outer cartons are designed to withstand more pressure or weight on one side without collapse. Some outer cases, e.g. wooden crates, should always be stacked so that all overhead weight is born by the ends. Corrugated board cartons are designed to bear vertical overhead weight on their four walls. The midsection of the top is usually the weakest point, and the cartons should not be stacked in a manner that will cause excessive weight on the foods at the carton midsection. A common mistake is to load pallets or cartons up to ceiling height, restricting air

flow along the return air passage over the top of the cargo to the evaporator fan. Where dissimilar sized packaging is used, or cargoes do not fill the container or trailer fully, it is recommended that additional empty cartons or some other material is used to fill up the void space so that the air passages remain uniform. In vehicles with canvas ducting on the roof, these should always be free and not restricted by the load. Most containers have bottom air delivery, and it is absolutely essential not to stow above the red load line, see also section 3.5 below. In most containers the load line is approximately 10 cm below the ceiling. In transport equipment with bottom air delivery, there must be a gap of at least 10 cm between the top layer and the ceiling. Unit load patterns should be designed to reduce the contact of the product with the walls and the floor, especially if the vehicle is without ribbed walls and without a ducted floor, e.g. a T-bar floor. Reducing the amount of surface contact will improve product arrival temperature and reduce the chance of product warming. Fig. 2.1 shows three basic pallet patterns in a vehicle or container. The loading pattern should also take into account that the vehicle might be scheduled for more than one receiver. Of course, the cargo intended for the first customer should be placed so it is easy to unload. Proper loading practices are also dealt with in section 7.2 below. 1.6 Pallets, slipsheets Most shippers and receivers have switched from handling of individual outer pack-

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Bulkhead wall

Bulkhead wall

Fig 2.1 Overhead view of three basic pallet or unit load patterns in a trailer og container

aging to unit loads on pallets or slipsheets.

racks, and provisions for forklifts and pallet jacks are necessary.

Unit loads offer the following advantages: • reduced handling • less damage to the packaging and to the foodstuffs inside • faster loading and unloading of transport vehicles • reduced pilferage

In transport equipment without a ducted floor, the pallets should be placed so they do not block air circulation under the load. The cartons and other outer packaging used in unit loads must have dimensions suitable to fit the pallets used. The object is to achieve utilization of 90-100 percent of the surface of the pallet with no overhang, more stable pallet loads, and reduced transportation costs. Cartons should be placed correctly and must not overhang the edges of the pallets, as this can reduce the strength of the paperboard cartons.

Unit loads may be standard wood pallets (Europallets 800 mm x 1200 mm, or Isopallets 1000 mm x 1200 mm), plastic netting around a pallet load of cartons, slipsheets, cornerboards (plastic or metal), plastic or metal strapping around cartons and cornerboards. Wood pallets must have sufficient strength to allow storage in three tier

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Slipsheets These cost less than pallets and also eliminate the cost of transporting and returning

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pallets. A special forklift is needed to transfer slipsheet loads to and from pallets at the shipper and at the receiver. If a receiver does not have the proper handling equipment, the packages are unloaded by hand onto pallets for storage. Outer cases on slipsheets are cross-stacked and film wrapped, or otherwise stabilized with cornerboards and strapping. 1.7 Mixed loads In practice, several commodities are sometimes stored in the same container or in the same trailer, even though the commodities may have different ideal tempera-

tures. For short-term storage and transport, this is usually of no significance. Dairy products, eggs, and fresh meat are highly susceptible to strong odours. Packaging reduces the problem, but most plastic materials allow quite a lot of odour to penetrate. Thorough cleaning and airing of vehicles or containers previously used for transporting fish, apples, cabbage, citrus fruits, onions and other odorous products is necessary. Odours from some products are nearly impossible to remove, and such products should not be transported if it is planned to shortly transport fresh meat etc.

Fig 2.2 Pallet and slipsheet

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2. MECHANICAL REFRIGERATION Mechanical refrigeration systems used in transport equipment usually operate with refrigerant R12 (Freon 12), and have reciprocating compressors mostly in the 5-8 hp range.

2.1 Principle of mechanical refrigeration The refrigeration process, or the refrigera-

tion cycle, includes four stages, as shown schematically in fig. 2.3: • Compression. In the compressor, the refrigerant gas is compressed, i.e. the pressure and temperature of the gas is increased. Then the high pressure gas is discharged into the condenser. • Condensation. In the condenser, the high temperature and high pressure gas is

Expansion Valve

Condenser

Evaporator

Compressor

High Pressure

Fig. 2.3 Schematic diagram of a refrigeration cycle

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Low Pressure

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cooled by means of air or water. The gas is changed into a liquid, still at high pressure. • Expansion. The expansion valve controls the flow of refrigerant, which it receives from the condenser (possibly via a liquid receiver) so that the correct amount of refrigerant passes to the evaporator.

Capacity reduction. In most modern transport equipment, the mechanical refrigeration unit has some sort of mechanism controlling the refrigeration capacity, in order to achieve prac tically constant air temperatures. This is essential for many chilled foods, where precise control at the lowest temperature the goods can tolerate is necessary.

• Evaporation. On entering the evaporator section the refrigerant passes from the high pressure side, through a small orifice in the expansion valve, to the low pressure side of the system. The low pressure causes it to evaporate. The latent heat of evaporation is extracted from the surroundings, for example from air passing the evaporator coils. The refrigerant gas is then drawn back to the compressor and the cycle is repeated.

A common way of reducing the refrigeration capacity of the refrigeration unit is hot-gas bypass, where a certain part of the hot refrigerant gas from the compressor is injected into the evaporator. There are several ways of controlling how much gas should bypass the condenser and is injected into the evaporator. The refrigeration unit runs continuously, this gives a more accurate control over the temperature but an increase in energy consumption compared to on/off control.

Refrigeration capacity Refrigeration capacity is the measure of cooling power available. Gross capacity is the total cooling done by the refrigeration unit. Net capacity (or effective capacity) is that available to the cargo space after removing the heat generated by evaporator fans and motors. The capacity is reduced as the evaporator temperature falls; the reduction is 3-4% per degree C at temperatures below 0°C.

Other methods of capacity control are cylinder unloading (see section 4.2 below), suction throttling, where the flow of refrigerant to the compressor is regulated, and control of the speed of the compressor motor. The latter method would result in lower energy consumption, but the system is still not fully developed.

The capacity is also reduced as the difference in temperature between the inside and the outside the vehicle increases. Generally, every 2°C rise in ambient temperature means that the minimum achievable internal temperature becomes 1°C higher. If the minimum achievable temperature is -20°C at an ambient temperature of 22°C, it will be -19°C at 24°C ambient.

In many trailers the compressor runs at high speed (HS) when the air is some degrees C warmer than required, and at low speed (LS) when the air temperature is close to the required temperature, see section 4.2 below.

2.2 Transport refrigeration units A transport refrigeration unit is a conventional circuit consisting of a compressor, a condenser, an expansion valve, and an evaporator coil, with the thermal expansion valve providing the primary control to the circulating refrigerant.

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culates in the reverse direction: top air delivery, see figure 2.11. The fans (1) force the air through the evaporator coil (2) which cools the air to the required temperature. The air then passes over the delivery air thermostat (4) used by the controller and out into the cargo space by way of the ducted floor (5). The most common form of ducted floor is known as T-bar floor, taking its name from the T-shaped cross section aluminium extrusions that form the floor, see fig. 2.9.

It is necessary to minimize the space occupied by the refrigeration unit, but at the same time securing the correct functioning of the unit. A cutaway view of a typical layout of a container refrigeration unit is shown in fig. 2.4. The internal air is circulated through the cargo space and the evaporator coils. The direction of the air flow is shown by the arrows. This is known as bottom air delivery, see fig. 2.9. In earlier containers and most long distance trailers, the air cir-

1 6

2 3

3 9

10

11 8

5 4 7

Fig 2.4 Cutaway view of refrigeration unit and container

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The air returning to the fans (1) is warmer than the delivery air as it has absorbed heat from the cargo space. The low pressure refrigerant in the evaporator (2) absorbs heat from (and cools) the air passing the evaporator coil, via the compressor (7) the refrigerant gas flows to the condenser (8) where the refrigerant gas is condensed by outside air forced through the condenser by the condenser fan (9). The now high pressure liquid refrigerant returns to the evaporator via the thermal expansion valve (not shown). On passing through the expansion valve from the high pressure to the low pressure side, the liquid refrigerant expands to a mixture of liquid and gas, which reduces the temperature of the refrigerant. The refrigerant in the evaporator coil again absorbs heat from the air passing the evaporator coil. The temperature recorder (10) measures and records the internal air temperature by a separate sensor (6), shown here in the return air passage but more often located in the delivery air duct, or both places, see section 3.3 below. 2.3 Thermostats In refrigerated transport equipment the temperature is maintained by a thermostat controlling the refrigeration machinery. The thermostat sensor measures the temperature (practically always an air temperature) and sends a signal to the controller which adjusts the refrigeration system. Generally speaking, the refrigeration system, if an on/off control type is switched on, or if a capacity controlled type is in it’s full capacity mode when the measured temperature rises to above the pre-set temperature. The refrigeration system is switched off or uses reduced capacity when the measured temperature falls below the pre-set temperature. Controllers are described in sections 3.3

and 4.2 below, where the importance of the location of the thermostat sensor is also stressed. 2.4 Defrosting During operation of the refrigeration unit, water vapour is transferred from the air and unwrapped food products, and the outer cases to the evaporator coils. If the temperature of the coils is below 0°C, then frost builds up, and the air circulation rate and refrigeration efficiency falls. Many units are fitted with timers to give a defrost at set periods, commonly once or twice a day. In some units, a differential pressure controller starts the defrosting process when the resistance to air flow across the evaporator reaches a pre-set value. In some units, the defrosting process is initiated when the difference between the evaporator temperature and the air temperature (return or delivery air) exceeds a pre-set value. The defrosting process, i.e. heating of the evaporator coil is provided for by electrical resistance heaters or by hot gas from the compressor bypassing the condenser, going directly into the evaporator coil. The air circulation fans in containers are turned off so that the heat is utilised in melting the ice on the evaporator coils, and not in heating the cargo. In most trailers, the fans continue during defrosting, but by closing of air vents, the circulating air is kept inside the evaporator section. The melt-water (melted ice) falls into a tray and then runs outside. By means of electric heaters, see (3) in fig. 2.4, the melt-water is kept above 0°C and can flow out. When the outlet is blocked, water may accumulate on the floor with potential damage to the outer cases and the food. The water on the floor may freeze and block the air flow leading to a rise in temper-

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ature of the food products. Of course, blocked outlets should not occur, and the outlets should be properly cleaned before the transport begins. During defrost, the temperature in the evaporator section rises, and this can usually be seen as a sharp rise and fall in temperature on the temperature recorder. 3. ISO INTERMODAL CONTAINERS During the last few years a large number of ISO intermodal containers have been

built. In 1990, about 180,000 refrigerated (thermal) containers are in operation, and the number of containers increases every year. A container essentially consists of three parts: • an insulated box • a refrigeration system • an air circulation and distribution system The work of international standardization

Clip-on unit

Fig 2.5 Porthole container showing ports, plenum and clip-on unit. The arrows show the air flow from bottom to top. (Bottom-air delivery)

Return air temperature sensor

Delivery air temperature sensor

Fig 2.6 Integral container with refrigeration unit built into the container and showing the positions of the temperature sensors for the controller/recorder. The arrows show the air flow (Bottom-air delivery)

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in the field of freight containers is carried out by Technical Committee 104 of ISO. The insulated box is mostly 6.06 m (20 ft) or 12.12 m (40 ft) or even 13.64 m (45 ft) in external length, and 2.44 m in width. The height of older containers is 2.44 m, but most new ones are 2.57 m (or even 2.74 m) high. Insulation is described in section 1.2 above. The floor of the container is normally made of T-bar channel sections to allow movement of air beneath the cargo, see figs.2.7 and 2.9. In most modern containers aluminium or stainless steel is used as a material for outer cladding. High grade stainless steel inner linings have replaced the damage prone glass reinforced plastic inner linings. 3.1 Types of containers There are several types of refrigerated containers, or thermal containers as they are described by ISO, especially • insulated containers, having no devices for cooling or heating (porthole containers, see below) • refrigerated containers, using a means of cooling such as dry ice and liquid nitrogen • mechanically refrigerated containers, having a refrigerating appliance such as a refrigeration unit as shown in fig. 2.4. Most mechanically refrigerated containers also have a heat-producing facility • removable equipment, such as clip-on units for porthole containers The two main types of refrigerated containers are the insulated container and the integral container. Porthole container. The insulated container is very often called a porthole container or an isothermic container. This is an insulated box with two holes or ports in the end wall, see fig. 2.5. Refrigerated air is delivered to the

Fig. 2.7 Container with slightly corrugated walls. The T-bar floor and the red load line can also be seen bottom porthole and is distributed into the T-bar floor channels. This is called bottom air delivery. The air flows from the T floor into and through the cargo space and leaves through a slot, 50-100 mm deep, which runs the full width at the top of the container rear wall. The air leaves through the top porthole. Provision is made for closing the portholes when they are not being used. On land, while awaiting loading onto a ship, a portable refrigeration unit ( a clipon unit) can be fitted to the end of the container. On board a cellular ship, i.e. a ship built to carry porthole containers, the containers are stowed below deck and are supplied with air from a central refrigeration plant which the ship’s engineers supervise. Sometimes porthole containers are shipped on deck with a clip-on unit attached and then they are essentially the same in operation as an integral container. Integral containers. Integral containers constitute more than 80% of refrigerated containers, and the proportion seems likely to increase in the future.

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The integral container has an electrically driven mechanical refrigeration unit, plugged into electric power at depots or aboard ships. The unit will often resemble the unit shown in fig. 2.4. Fig 2.6 shows (schematically) an integral container with bottom air delivery, see fig. 2.4 and fig. 2.9. During land transport, the all-electric refrigeration units require the support of a diesel engine driven generator set (genset). Current designs of gensets include • clip-on gensets, mounted over the front of an electric unit • nose mount gensets, fitting within the ISO profile • undermount gensets, mounted beneath the chassis on which the container is being transported.

Fig. 2.8 Clip-on genset Two types are seen in fig. 2.8

Fig. 2.8 Undermount genset

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All refrigerated containers must be suitable for the carriage of both frozen and chilled foodstuffs on different occasions. Therefore, most containers are able to maintain temperatures from about +20°C to about -23°C.

the process for maintaining prescribed temperatures. Cold air is constantly circulated through the cargo space to remove transmitted heat. For unwrapped products water vapour will be removed as well.

3.2 Air ventilation in containers Ventilation during transport of the chilled and frozen foods dealt with in this book, is internal ventilation (forced air circulation) with cold air to maintain the required product temperature.

Bottom-air delivery Most containers are equipped with bottom air delivery. The air is forced down the bulkhead and through the T-bar floor, under and up through the load. The air returns to the evaporator over the top of the load and through the top of the bulkhead, see fig. 2.5 and fig. 2.9.

For the foodstuffs dealt with in this book, it is absolutely essential that the fresh air ventilation is closed. The fresh air vents should only be opened during transport of, for instance, fresh fruit and vegetables. Internal ventilation is an essential part of

For maximum efficiency with bottom-air delivery, the following factors are important: • the product should be loaded tightly together

Board or plate

Board or plate T-bar floor

Fig. 2.9 Pathways of air in trailer with bottom-air delivery

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• Adequate space must be left between the top of the load and the ceiling for air to return to the evaporator. Adequate space means at least 10 cm, and when the load is kept below the red load line, this will be attained. If the gap is less than 10 cm, the air circulation is restricted, resulting in foods at the door end being carried at higher temperature than desired. This effect will be even greater if the cartons bulge and allow the air to short-circuit through the resultant vertical gaps near the refrigeration unit. • It is important to block unloaded space over the T-bar floor between the end of the load and the rear doors to maintain air pressure under the load. Heavy paperboard is suitable for this purpose.

3.3 Controllers in containers The main object of food transport is to assure the minimal loss of quality during transport, and therefore, precise control at the lowest temperature the foods can tolerate is necessary. In addition to the primary control provided by the thermostatic expansion valve, there are a number of alternative additional controls providing a choice of sophistication and accuracy. The operation of the refrigeration system depends on its construction and control system. It is therefore important that the handling agent is familiar with the directions supplied by the manufacturer.

Temperature control systems Set-point. The set-point is the temperature at which the controller is set. However, the temperature in the cargo space depends on where the temperature sensor for the controller is placed. Most of the earlier re-

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frigeration units are controlled from a temperature sensor located in the return air (see fig. 2.6), i.e. the air coming back to the refrigeration unit after absorbing heat from the cargo space. This is called return air control. When transporting chilled foods, most modern refrigeration units are controlled by a sensor located in the delivery air stream, i.e. the air leaving the unit and about to enter the cargo space. This is called delivery air control. These units retain a sensor in the return air for control when transporting frozen foods. It must be emphasized that the set-point temperature should not be confused with the product temperature. The air warms up as it moves through the cargo space, and the temperature of the return air will be higher than the temperature of the delivery air. Exporters must understand this difference when they make requests to a shipping company regarding the setting on a container. Some exporters do not differentiate between the set-point and the food product temperature. Return air control Most units that are controlled from a return air sensor operate in an on/off mode. When the temperature of the return air falls to the set-point, the controller switches the refrigeration unit off. To avoid short-cycling, i.e. switching on and off too frequently, some refrigeration units are not switched on again until the air temperature becomes 1-2°C warmer than the pre-set temperature. This means that the temperature of the return air will cycle 1-2°C, but the delivery air will cycle more than that, sometimes 3-6°C. Delivery air control. Most of the units that are controlled from a delivery air sensor, have some method

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of (controlling) reducing the refrigerating capacity of the unit, see section 2.2 above.

portable) PC. This allows much more accurate records to be obtained and has the potential for more reliable control.

Combined control A theoretical good control is an electronic delivery air controller and a mechanical return air controller, operating together. The delivery air is kept at the temperature setting on the delivery air controller, but if the return air temperature falls to the setting on the return air controller, the unit is switched off. In practice, this type of control may give problems, mainly due to a poorly set or calibrated return controller.

The controller often provides other facilities, such as testing the machine’s functions prior to loading as a part of the PTI (Pre-Trip Inspection). If the temperature is set to a temperature between +20°C and -5°C (-4°C to -6°C depending on the manufacturer), it is automatically decided that the delivery air sensor shall be used to control the refrigerating unit. If the temperature is set to -5°C or colder, the control is taken over by the return air sensor. The evaporator fans often run at full speed when the setpoint is -5°C or warmer, and at reduced (half) speed when the set-point is colder than -5°C. A typical control system works in the following way:

Mechanical safety thermostats that should secure against freezing of chilled foods, need careful supervision to obtain the best results. If set inaccurately, the refrigeration unit may operate in an on/off mode with the result that the cargo is transported at a warmer temperature than desired. The modern electronic controllers described below ensure a combined control without significant problems. Modern control in containers. With advances in electronics and microprocessors, many newer refrigeration units are fitted with controllers/recorders that have both a return air and a delivery air thermostat feeding control signals to an electronic, often computer based, controller. The controller adjusts the refrigeration unit, the fans, and the overall capacity of the refrigeration unit to give a very precise delivery air temperature. The signals (temperatures) from the two thermostat sensors are recorded and stored in memory, along with other information, for later retrieval. Such microprocessor controllers have a digital readout, and can display the temperatures and other events stored in the memory. Printout is obtained by means of an ordinary (or

The refrigeration unit operates on full cooling capacity until the delivery/return air is a little above the set-point. Then the unit will operate on reduced (e.g. 50%) capacity until for example 0.1°C above the set-point, where further reduction in capacity (to for example 25 %) will be introduced. If the delivery air becomes a little (e.g. 0.3°C) colder than set-point, a heating cycle will be introduced. By means of such systems, the delivery air can be maintained within 0.2°C of the set-point. When the set-point is -5°C or colder, heating (and sometimes also capacity reduction) is locked out, and the unit will be de-energized when the return air reaches a little (e.g. 0.6°C) below set-point. The control system is somewhat similar to the system used in modern trailers, see section 4.2 below. Some modern ISO containers have controllers that will allow information about

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individual containers to be obtained through pulses down the power lines. This will enable integral containers to be monitored from the ship’s control room. A broad band high data rate system will be included in ISO’s remote reefer container monitoring standard.

Experimental results have shown that actual maximum cargo temperature ranges are about twice the difference between delivery air and return air. The temperature difference between the coldest and the warmest foods can be about 1.5°C.

Temperature differentials. This refers to temperature differences within the cargo space. These differences depend on the volume of circulating air, the effectiveness of floor design, the stacking pattern of cargo, and the control system.

3.4 Temperature recording in containers Any temperature measurement, for example at border crossings or on arrival at destination, only indicates the temperature at that moment in time, and cannot disclose what might have occurred during the journey. There are a number of possible causes of failure in long distance transport, such as a refrigeration unit breakdown which has been repaired but not reported, or the unit deliberately has been switched off. A temperature recorder indicates the time-temperature history from loading to unloading and would show such incidents. Temperature recorders normally record air temperatures and this is often considered sufficient, although it must not be overlooked that correct return or delivery air temperatures do not prove that product temperatures throughout the load are as required. Some shipping companies place one, two or three independent temperature recorders in the load in order to record product temperatures.

The effectiveness of temperature control is judged by: • The temperature at the thermostat sensor. Constant (and correct) temperature at the thermostat sensor, which in chilled cargoes should be in the delivery air. The average temperature over an hour should be within +/-0.1°C, with short term variations of max. +/-0.5°C. • The temperature spread across the width of the vehicle. The spread should be within a range of +/-0.3°C. • The temperature range through the cargo. The laws of physics dictate that completely uniform temperatures can never be achieved. Greater awareness of what is a normal and reasonable temperature distribution is needed, especially as there is now an increased awareness of the importance of maintaining the correct temperatures of chilled and deep frozen foods during storage and transport. The temperature difference between delivery and return air can be below 1°C. This difference can be calculated from the flow rate (air changes per hour), the heat input (the vehicle heat leak, in W/K),specific heat capacity and density.

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Recording systems Temperature recorders must be sufficiently robust to withstand the vibration and adverse conditions encountered during transport, loading and unloading. At the same time the recorders should be sufficiently accurate and as tamper-proof as is practically possible. Most containers are fitted with a mechanical circular chart recorder, 150 or 200 mm in diameter, that records the temperature

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of the return air or the delivery air. The recorder is frequently combined with the controller; the principal manufacturer is “Partlow” and this company’s name has become a general term to describe this type of recorder/controller. These mechanical recorders can be in error up to 1°C. Small errors occur through wear in the mechanical linkages. Larger errors are usually the result of poor adjustment. As mentioned above, see section 3.3, modern electronic controllers record and store delivery air and return air temperatures. Recording of temperatures in the cargo Mechanical temperature recorders located in the cargo, for example in one of the transport cartons, have been used for decades. The system is still used, particularly a recorder using a battery to drive a pressure sensitive chart, and a pen to make the recording. Such recorders can be bought or leased. Modern independent temperature recorders are electrical devices, often with a memory where the recorded temperatures are stored. Such devices are often called temperature loggers. After the journey, the logger is connected to a computer and the time-temperature history can be shown or printed out. There are several such devices and many of them are very robust and able to operate at low temperatures. They can also be bought or leased. A logger can give a very good picture of the product temperature at the point where it is placed in the cargo. One logger is not enough to give an exact picture of the temperature in the whole cargo, unless it has several sensors. However, it

is normally considered sufficiently when a single logger shows temperatures that are at the required level. There is disagreement about where independent recorders should be placed. If there is concern for freezing injury, then the recorder should be placed near where the delivery air enters the cargo space. If there is a desire to record the mean product temperature, then the recorder should be placed in the centre of the stow. If there is concern that packages near the door are getting too little air and may be too warm, then the recorder should be placed in a carton near the door - at the bottom for a top air delivery container or at the top for a bottom air delivery container. To avoid confusion, it would be best to place the recorders at half height in the container. However, for simplicity, the recommended position is 1-1.6 m from the rear doors, at half height and in the centre line of the container. The carton must be clearly marked to ensure that the recorder is recovered, and somebody must be given the responsibility for forwarding the rather expensive recorder to the appropriate place. Temperatures recorded by independent recorders should be regarded more as devices to record “catastrophes” than to give representative temperature records. They are accessible only at the end of the journey and no corrective action can be taken if the vehicle or container is malfunctioning. In some countries and for some foods, it is mandatory to place a recorder in the load. 3.5 Loading of containers The foodstuffs must always have the required temperature at loading and the

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Fig. 2.10 Trailer with top-air delivety, showing the air flow around the cartons stowed in a block

outer cartons should be stowed in a block, so the air can pass above and beneath the block. The cartons should be arranged in order to ensure a stable cargo, but at the same time must be secured so that the air circulation between the cartons and the wall is not restricted. Most earlier containers have some form of wall battens to keep the cargo from being in direct contact with the walls and to allow air to flow over the walls to remove the heat being transmitted into the container through the walls. To cut maintenance costs many containers are being built now with smooth or slightly corrugated sidewalls. There is some evidence to suggest that less air flows over the walls of smooth-walled containers than over those in containers with wall battens, re-

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sulting in higher temperatures in transport cartons against the walls. Marine containers are marked with a height limit, the red load line mentioned before, which should never be exceeded. Further information on loading can be found in sections 1.5 and 1.6 above, and in section 7.2 below.

4. PRIMARY DISTRIBUTION VEHICLES (TRAILERS) Food products are usually transported from the factory or a primary cold store to cold stores and/or distribution depots by a large refrigerated vehicle, the refrigerated vehicle usually being at least 11-12 m in length. Such a vehicle is usually referred to as a primary distribution vehicle, trailer or a trunker.

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The official formula for calculating effective refrigeration capacity is: Eff. ref. capacity = Sm x K-coefficient x ∆ T x SF where Sm = mean surface area (m2), K-coefficient is defined in section 1.2 above, ∆ T= difference between ambient air and internal air temperatures, SF=Safety Factor. In the ATP the minimal Safety Factor is 1.35 to 1.75, but it seems advisable to apply higher factors, e.g. 2 to 2.5 for ATP class C (-20°C), and 4 to 5 for ATP class A (down to about 0°C). Provided there is good internal air circulation, the effective refrigeration capacity for the transport of quick frozen foods should be at least 4100 W for a body volume of 60 m3, and at least 4800 W for a body volume of 70 m3. In the calculation of these figures, a safety factor of 1.75 has been used. By using the recommended factor 2.2, a volume of 60 m3 demands about 5100 W and a volume of 70 m3 demands about 6000 W. Trailers, Trunkers. Trailers usually have a mechanical refrigeration system, see section 2 above. In principle, trailers and integral containers are very similar, the main difference being that containers built for intermodal service have all the machinery recessed into the front section of the container, see fig. 2.6. By remaining within the envelope of the ISO prescribed dimensions the refrigerated containers can be interchanged with all other containers and in particular stacked above and below deck on cellular containerships. The trailers refrigeration unit is usually driven by a diesel engine. Some units may be plugged into electric power, for example while in depots overnight.

Some units operate via the truck’s engine, directly or via a generator, but these systems are mainly used for shorter distances. Two types of thermostatically controlled mechanical units are most commonly used on road vehicles for long distance transport. One type has the compressor, power unit, condenser, and other accessories mounted on the nose of the vehicle, with the evaporator coils and air fans directly inside the front of the vehicle, see fig 2.10. The other type (a split unit) has the compressor, condenser, etc. under the frame of the vehicle, again with the evaporator coil and fans inside the front of the vehicle.

4.1 Ventilation in trailers Ventilation during transport of the chilled and frozen foods dealt with in this book, is normally forced air circulation with cold air to maintain the required product temperature. The air temperature is pre-set on the controller (the thermostat), see section 4.2. Internal ventilation is an essential part of the process for maintaining prescribed temperatures. Cold air is constantly circulated through the cargo space to remove transmitted heat. For unwrapped products water vapour will be removed as well. Top air delivery In most transport vehicles with mechanical refrigeration, top air delivery is the conventional method, see fig. 2.10 and fig. 2.11. The cold air from the refrigeration unit exits at the front ceiling and the air must be at a relatively high velocity to carry it all the way to the rear of the vehicle.

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To obtain improved air circulation and product temperatures the following factors are important: • Air ducts should be used to assure air delivery to the rear of the vehicle and to assure even air distribution. • Open space, it is suggested that 5 cm should be left between the rear doors and the load to allow adequate air circulation. The existence of such a rear air path is dependent on good loading. In order to guarantee this air path, it is recommended that a minimum of 25 mm wide channels be incorporated into the rear doors. • The top layer should be loaded so as to prevent short-circuiting of the air back to the evaporator. • The cold air should be allowed to circulate down the sides of the load to absorb the heat conducted through the walls. For vehicles without ribbed walls, some form of strip or batten on the sidewalls is recommended to allow air circulation between the wall and the load. • Bracing at the rear doors should prevent the load from shifting. The installation of angle irons over the full length of the cargo space is recommended, see section 7.2 below. • The floor design must provide an adequate air flow under the load. This could be a T-bar floor as shown in fig. 2.9, or other types of ducted floors, such as the so-called “alhut” profiles. • There should be some arrangement at the front, e.g. a solid bulkhead, to allow the air to return to the evaporator. Some vehicles have a false bulkhead with metal

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screen or holes at the bottom for return air passage. In some vehicles, wood pallets are set on their end, with the stringers vertical, between the bulkhead wall and the first stack of the load.

4.2. Temperature control in trailers The operation of the refrigeration system depends on its construction and control system. It is therefore important that the handling agent is familiar with the directions supplied by the manufacturer. Temperature control systems Set-point. The set-point is the temperature at which the controller is set. However, the temperature in the cargo space depends on where the temperature sensor for the controller is placed. Refrigeration units in trailers are controlled by a temperature sensor located in the return air, i.e. the air coming back to the refrigeration unit after absorbing heat from the cargo space. This is called return air control. Delivery air control, see section 3.3 above, is seldom used in trailers. It must be emphasized that the set-point temperature should not be confused with the product temperature. In warm climates heat will be coming through the insulation, the door if it is not sealed and in the case of respiring cargoes such as fruit and vegetables from the product, consequently the air warms up as it moves through the cargo space, and the temperature of the return air will be higher than the temperature of the delivery air. Thus, to maintain the required average temperature of the food in the vehicle, the temperature on a return air controller must be set higher than on a delivery air controller. If the required temperature of the load should be around 4°C, a delivery air controller should be set at about 3°C, while a return air controller should be set

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Control modes in 4-stage system

Temperature

HS, Cooling

Control modes in 6-stage system

HS, Cooling a

LS, Cooling

LS, Cooling b c d

LS, Heating

Setpoint

LS, Cooling, Unloading LS, Heating, Unloading LS, Heating

e HS, Heating

Decreasing Temperature

Increasing Temperature

at about 5°C. However in arctic climes heat may be escaping through the insulation and arctic cold air entering through any gaps in the door. In this case the set point must be adjusted the other way. Control systems. Some units operate in an on/off mode. When the temperature of the return air falls to the set-point, the controller switches the refrigeration unit off. To avoid short-cycling, i.e. switching on and off too frequently, the refrigeration unit is not switched on again until the air temperature is 1-2°C warmer than the set point temperature. The delivery air temperature will cycle more than that, sometimes 3-6°C. In most cases the evapora-

HS, Heating

Decreasing Temperature

Increasing Temperature

tor fans run continuously to provide a constant air change in the cargo space. Most newer refrigeration units are driven by a diesel engine running continuously. The compressor, usually a four cylinder compressor, runs at two speeds, high speed (HS) which is about 2200 rpm, and low speed (LS) which is about 1450 rpm. Naturally, low speed operation saves energy and hence fuel. In many refrigeration units, a 4-stage or 6-stage thermostat control system automatically regulates the unit. A typical 4-stage control system operates in the following way: When the thermostat sen-

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sor in the return air measures a temperature some degrees (often about 3.5°C) warmer than the set-point, the unit cools at high speed. When the return air temperature gets below point a in the figure above, the unit runs at low speed, still cooling. This continues until the return air gets colder than the set-point (point c), or, more correctly, colder than point d, which is about 0.8°C colder than the set-point. The unit then is switched into low speed heating. When the return air gets warmer than point b (about 0.8°C warmer than the set-point) the unit is switched to low speed, cooling. High speed heating is used when chilled foods are transported through very cold regions, e.g. ambient temperatures below -10°C, as this could cause freezing of some foods. However, heating of the air when the return air becomes some degrees colder than the set-point may have some disadvantages, for example when deep frozen foods are loaded with a temperature of -25°C and the thermostat is set at -18°C. As frozen foods should be stored and transported as cold as possible, it is a waste of energy and has a negative (although very small) influence on product quality to heat the air and the food products. The thermostat should be set a little colder, or there should be a system where high speed heating cannot be introduced when the thermostat is set below -13°C. This system is used by some manufacturers of refrigeration units. Other control systems include a “heat lock-out” option. In some modern units, a 6-stage control system is used, see the figure above. Here, the refrigeration capacity is reduced by means of cylinder unloading, further reducing the fuel consumption. The unit

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will usually start at HS, cooling and change to LS,cooling. When the return air temperature gets below point b in the figure above) two of the four cylinders are unloaded, and in many cases the unit can operate with low speed, cylinder unloading, cooling or heating, most of the time. This saves energy and also results in a more even temperature in the cargo space. Such control systems normally allow a time lapse of some minutes (e.g. 6-10 minutes) from the return air temperature increasing to a level where more refrigeration capacity is indicated, until cylinder unloading is finished and low speed, cooling is started. The evaporator fans normally run with a speed proportional to the compressor. In some units, a constant air flow option is incorporated in the control system as there is a special or separate electrical evaporator fan motor. Thus, high speed air circulation can be maintained all the time, even though the compressor may run at low speed 70% of the time. Higher air circulation should result in an improved air distribution, minimizing temperature variations. It is recommended that the air circulation should be at least 60-80 times the body volume per hour for all frozen food cargoes as well as for sensitive loads at about 0°C, e.g. fresh meat. At low speed, 40-50 times the body volume per hour may be sufficient. As mentioned in section 3.3 above, the effectiveness of temperature control is judged by: • Constant (and correct) temperature at the thermostat sensor.

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• The temperature spread across the width. • The temperature range through the cargo. Greater awareness of what is a normal and reasonable temperature distribution is needed, especially as there are now increased demands on and specifications for the temperature of chilled and (deep) frozen foods. The difference between delivery and return air can be below 2°C, but is sometimes higher. The temperature difference between the coldest and the warmest foods can be about 2-3°C.

4.3 Temperature recording in trailers Any temperature measurement only indicates the temperature at that moment in time, and cannot disclose events that may have occurred during the journey. There are a number of possible causes of failure in long distance transport such as a refrigeration unit breakdown which has been repaired but not reported, or that the unit has been deliberately switched off (because of noise problems). A temperature recorder indicates the timetemperature history from loading to unloading, and would show such incidents. Temperature recorders generally record air temperatures, and this is normally sufficient, although it must not be overlooked that correct return or delivery air temperatures do not prove that product temperatures throughout the load are as required. In many newer units, temperature recorders are included in the control systems. Partlow recorder/controllers, see section 3.4 above, are often used. Electronic controllers including recording systems are found in many new refrigeration units, see section 3.3 above. Such controllers also record defrosting periods and provide several other facilities.

An alternative system is to fit temperature sensors permanently into the walls and ceiling, with wires connecting the sensors to a central unit. The driver of a trailer is able to read the temperature easily, and a signal (red light) could be started if a fixed temperature limit is exceeded. Print-out of the time-temperature history from loading to unloading can be given to the receiver. As mentioned in chapter 1 section 6.2, it is likely that suitable temperature recorders will be mandatory in transport vehicles in the EEC-countries within a few years, at least for long distance transport of deep (quick) frozen foodstuffs. Recording systems Temperature recorders must be sufficiently robust to withstand the vibration and adverse conditions encountered during transport, loading and unloading. At the same time the recorders should be sufficiently accurate and as tamper-proof as is practically possible. For further information, see section 3.4 above. Positioning of temperature sensors In transport equipment with mechanical refrigeration, the temperature sensor is usually placed in the return air. The return air temperatures will often reflect the average temperature of the cargo, but there could be considerable temperature differences between the warmest and the coldest food products. This could be the case if the air flow is not being correctly distributed throughout the cargo space, or if the foods were not as cold as required at loading. An incorrect stowage system can cause faulty air distribution, see section 1.5 above. It is clearly an advantage to record two (or more) temperatures in transport vehicles. One sensor should be close to the

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refrigeration unit, preferably in the return air. Another one should be placed at the wall or roof of the vehicle, so that the air temperature of at least one point well removed from the evaporator can be monitored. This gives some problems as loading and unloading could damage the sensor. Permanent fixing of the sensors will minimize damage and malfunctions, and cause minimum disturbance during loading and unloading. The only disadvantage is that no direct measurement of food temperature is taking place. However, the recordings should indicate that the cargo space temperatures have been maintained satisfactorily during the journey. It is also advisable to record the door openings The alternative system mentioned above should give a very good picture of temperatures during the journey. Recording of product temperatures The temperature recording devices described in section 3.4 above would be as valuable in road vehicles as they are in containers. The recommended position of such recording devices is in the top carton in the last tier and in the centre line of the trailer. The carton must be clearly marked to ensure that the recorder is recovered, and somebody must be given the responsibility of forwarding the sometimes rather expensive instrument to the appropriate place. Temperatures recorded by independent recorders should be regarded more as devices to record “catastrophes” than to give representative temperature records. They are accessible only at the end of the journey and no corrective action can be taken if the vehicle or container is malfunctioning.

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It has been proposed to make the use of time-temperature integrators mandatory. Such devices are fixed to the packaging, for instance to each transport carton, and they react to temperature, for example a temperature dependent colour reaction. Thus, it can be seen directly what timetemperature history the integrator (and the carton) has been exposed to. Some of these integrators are cheap, e.g. about $ 0.3 each, but until now such integrators have had limited usage. 4.4 Loading of trailers The most important factors to take into consideration during the loading process are time and contact with ambient air. Ideally, the loading bay should be kept at the same temperature as the required carriage temperature, and the trailer should be connected to the cold room via a port door with seals. Chilled and frozen foods should not be allowed to remain outside the cold room unnecessarily while waiting to be loaded into the trailer. The foods must be at the correct temperature when loaded and transport cartons should be stowed in a solid block. It is self evident that whatever packaging is used, it must be secure. What is important is that while remaining secure, the packaging must allow air to circulate freely around the periphery of the vehicle and in the area of the door. The important criterion here is to have uniform distribution of air throughout the load. This requires the cargo to be uniformly stowed. As mentioned in section 1.2 above, the maximum external width of trailers in the ATP class FRC is now 2600 mm in Europe. This gives an effective internal width of more than 2400 mm, thus making it possible to place two pallets,1200 mm wide, side by side.

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For further information on loading, see sections 1.5, 1.6 and 1.7 above and section 7.2 below.

5. OTHER TYPES OF REFRIGERATION SYSTEMS Refrigeration systems other than mechanical refrigeration are sometimes used to transport chilled and frozen foods, especially by road and in local distribution.

5.1 Cryogenic refrigeration Cryogenic systems or total loss systems involve cooling, storing and transporting the refrigerant to another location before making use of it. After the refrigerant has been used, the refrigerant is lost to the atmosphere, hence the descriptive term: total loss.

frigeration medium in some vehicels. The most frequent use is in frozen food and ice cream delivery vans, and in smaller containers, see section 6 below. Solid carbon dioxide may be placed within individual outer packaging. For local distribution and where there is a requirement for separate temperatures in the same vehicle, direct expansion of cryogenic gases can be used as the means of refrigeration. These systems usually use liquid nitrogen or carbon dioxide. The controls are particularly simple and reliable, but it is not always cost effective. A thermostat injects the liquid gas behind a shield in the cargo space in order to prevent produce coming into direct contact with the exceptionally low temperature of the gas.

Cryogenic refrigeration systems use liquid nitrogen or liquid or solid carbon dioxide. Liquid cryogenic systems usually operate by having liquid refrigerant in pressurized tanks. A temperature sensing element in the vehicle activates a controller which releases the liquid refrigerant through a spray nozzle at the ceiling of the vehicle. When the temperature has been reduced to the pre-set temperature, the temperature sensing element sends a signal to the controller to shut off the flow of refrigerant.

Several precautions must be taken where carbon dioxide or nitrogen may have replaced oxygen in a transport vehicle. Several minutes should be allowed before anybody enters a trailer (or container) after the doors are opened to allow replenishment of oxygen to a normal concentration.

Carbon dioxide gas is heavier than atmospheric air and settles quickly to the floor. Fans should be operated continuously in carbon dioxide refrigerated loads of chilled products to prevent too low temperatures (freezing injury) in the bottom layers and too high temperatures in the top layers of the load.

Cryogenic systems have fewer moving parts to maintain and replace than mechanical systems. In cryogenic systems, it is difficult to prescribe the most suitable position for the sensors to be used in temperature monitoring or recording.

Solid carbon dioxide or dry ice in the form of blocks, snow, or pellets is used as a re-

Because of the limited number and distribution of suppliers of refrigerant this type of refrigeration is used primarily in journeys of less than one days transit time.

5.2 Eutectic plates Eutectic plates contain a solution of water and various chemicals such as salts or

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glycols. Such solutions should have a suitable melting point and be non toxic. The eutectic solution solidifies at a temperature lower than the required carriage temperature; often the solidifying temperature is commonly around -30°C. This is achieved by circulating a refrigerant through the coils enclosed in the plates before the vehicle is loaded. This is done either at a depot or dockside central plant condensing unit, or a closed circuit truckmounted condensing unit. The plates are mounted on the vehicle walls and ceiling and during the run the eutectic solution melts, providing the refrigerating effect necessary to maintain the required temperature. The plate system is sometimes augmented with a blower device to provide forced air circulation in combination with the hold-over facility of the plates. This combination can help bring about faster temperature reduction than can be achieved with plates alone. However, fans are seldom used in these smaller vehicals equipped with eutectic plates as they rely on natural convection to provide air circulation. As mentioned above, the mandatory use of suitable temperature recorders will not cover local distribution. The main reason is that it is difficult to prescribe where the temperature should be measured to give the most accurate picture of the temperature conditions in a local distribution van where the doors may be opened 25-50 times a day. 5.3 No refrigeration system Insulated containers (or vehicles) with no refrigeration system must only be used for short journeys (less than 2-3 hours) or when ambient temperatures are close to

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the recommended transport temperature throughout the journey. However, insulated trailers are often used for long distance transport of fresh fish, which must then be transported in melting ice. Here, the air temperature in the cargo space should be 1 to 3°C, see chapter 3 section 5.5.

6. OTHER TYPES OF TRANSPORT EQUIPMENT The equipment described above is intended for long distance transport. Perishable foodstuffs are distributed in other types of equipment. The following are types of equipment used in local distribution.

6.1 Secondary distribution vehicles or delivery vans These are loaded at the distribution depots and deliver to shops and stores. Delivery vans may have mechanical, eutectic plates or cryogenic refrigeration systems. The use of eutectic plates are common in this type of vehicles. In local distribution, it is common to have mixed loads with retail packed chilled meats, fresh fruits and vegetables, frequently unwrapped, and bread also often unwrapped being distributed in the same vehicle with the temperature set at about 5°C. In some countries the authorities may prescribe special precautions such as a physical separation between meat products and the two other groups. When products demanding lower temperatures are distributed together with other foodstuffs in a vehicle at say 5°C, it is necessary to use an insulated box within the vehicle to store the lower temperature goods. Thus, deep frozen foods (-18°C or colder) or MAP meat are carried in an insulated boxes within the 5°C controlled vehicle.

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Special precautions must be taken for fresh fruits and vegetables, among the considerations are ethylene production and type compatibility, see the book GUIDE TO FOOD TRANSPORT, FRUIT AND VEGETABLE.

6.2 Equipment with several transport temperatures Transport equipment (mostly trailers) with two or three separate compartments can be used to carry loads of food products with different temperature requirements. The conditions provided by three compartment vehicles may include -18°C, 0°C, 10°C, or ambient for foods not requiring refrigeration. The frozen compartment is usually located at the front of the vehicle adjacent to the refrigeration unit. Movable bulkheads are placed between the compartments. Ventilation between compartments provides temperature control for the nonfrozen products. However, this means that warm air is returned to the refrigeration unit in the frozen food compartment, giving condensation problems and warming of the frozen food products. Side doors are needed for access to the forward compartments when the vehicles are inspected at ports of entry or used to make multiple deliveries on a single run. Some modern trailers have a mechanical refrigeration unit and three separate evaporators, one in each compartment. This enables a free choice of temperature in each compartment. For local distribution, different temperatures can be provided in the same vehicle by insulated containers. Such containers may be small, e.g. 180 cm x 60 cm x 40 cm, and their use for chilled as well as for deep frozen foods is well known.

However, they should not be used for long distance transport. 6.3 Thin wall equipment Thin wall vehicles are characterized by a sidewall thickness of less than 45 mm. In conventionally insulated equipment, the wall thickness is about 70-80 mm. In thin wall vehicles roof and walls have a thickness up to 200 mm, to achieve a total K-value equal to or less than 0.4 W/m2x°C. The advantage of thin wall vehicles is that they can accommodate two pallets, 1200 mm wide, side by side in the cargo space. The internal width must be at least 2430 mm wide to allow for rapid loading and unloading. The maximum external width in Europe has recently become 2500 mm. A thin wall vehicle with a usable length of 12.2 m can accommodate 24 pallets 1200 mm x 1000 mm, whereas a conventional vehicle can accommodate only 22 pallets. This implies an increase of about 10% in load capacity, provided the weight limit is not exceeded. Similarly, 30 Europallets (800x1200 mm) can be transported in the thin wall trailer, but only 25 in the conventional trailer, i.e. an increase of 20%. As mentioned before, insulation ageing for all types of insulated equipment is a persistent recurring problem, and with thin wall vehicles it could be of considerable significance. Thin wall vehicle insulation deteriorates at a rate of about 6% per year compared to about 5% for conventional vehicles. The initial K value is 0.350.38 W/m2 x°C for thin wall vehicles, and it could be difficult to get ATP re-certification after 6 years. However, the above-mentioned improvements in polyurethane insulation technol-

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ogy may solve this problem, see section 1.2 above. Another factor which can be influenced by equipment design is the air circulation rate inside the cargo space. A figure often quoted for a 40 ft container is 60 air changes of the empty container per h or about 3600 cu.m per h. At 30°C ambient and -20°C internal temperature, the return air temperature will be about 1.8°C warmer than the delivery air. The air flow at the side walls of thin wall vehicles should be higher than in conventional vehicles and an increase to 80-90 air changes per h should secure a minimum air change per h even with an air restriction from a part frosted evaporator. This would result in increased fan power and a reduction in the net capacity of the refrigeration unit. In thin wall vehicles, the cargo should not lean against the side walls, and a gap of at least 6 mm between product and side walls is essential. However, permanent battens have been eliminated in most 40 ft equipment due to problems of loading pallets. A possible solution to the enhanced requirement for increased air flow in thin wall vehicles would be to use bottom air delivery.

7. CODE OF GOOD TRANSPORT PRACTICE

7.1 Transport equipment before loading Many carriers check their transport equipment before presenting it to the shipper for loading. This procedure is commonly used by responsible owners of ISO containers. Known as the Pre Trip Inspection,

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PTI or just the Pre Trip the condition of the machinery is normally subjected to a functional test. The modern electronic control unit can perform some of these routine tests automatically. The shipper should also check the equipment for: • cleanliness - the cargo space should be clean. There should be no odour from previous shipments as this could result in off-odour or off-taste, see section 1.7 above. It must be checked for debris blocking drain openings or air circulation along the floor, etc. It is usual and good practice to wash the interior with hot water or wet steam between each journey or on a weekly schedule if in constant use on multiple short deliveries. The interior of the transport vehicle must be made of and repaired with materials approved for contact with foodstuffs; this is especially necessary when transporting carcass meat and other unwrapped foods. Some countries demand that transport vehicles and hooks used for hauling meat should be cleaned and inspected before loading. In order to reduce the number of microorganisms present and to dissolve fat particles, some countries recommend or demand that the wash water is 82°C or warmer. This procedure should not be used in transport equipment with some types of plastic inner linings. Sanitizers may be used if approved by the relevant authorities in the exporting country and in the importing country. The outside of the vehicle should be kept clean in order to reflect radiant heat, see section 1.2 above. • damage - walls, floors, doors, ceilings should be in good condition, as damage can let in the outside heat, moisture, dirt, etc. Broken places in the wall and floor may house dirt and microorganisms, and are difficult to clean.

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Damage to the inner walls may allow the ingress of moisture into the insulation which will lead to a higher K-value, i.e. a deteriorated insulation. Operation and the conditions of the doors, ventilation openings, and provisions for load locking and bracing should be checked. • temperature control - the refrigeration units should have been recently calibrated. • air tightness should be checked by having someone in the cargo space with the doors closed, to check for light. Door seals and floor drain caps should be checked regularly and repaired or replaced as needed. A solid return air bulkhead should be installed at the front of a trailer. A heating device should be available for transportation of chilled foods, sensitive to freezing injury, in areas with extreme cold weather. Equipment with top air delivery must have a fabric air chute or metal ceiling duct in good condition. • the thermostat, temperature recorder etc. should be checked. A temperature sensor from a calibrated instrument should be placed in mechanical contact with the sensor that is being checked. The two readings are compared and necessary adjustments made. There may be some problems here because:

before loading to ensure the load has been properly pre-cooled. In some cases, the product temperature can be measured between the packs, in other cases it is necessary to use the destructive method, see chapter 1 section 7.2.

7.2 Proper loading practices The food products must have the desired temperature prior to loading into the vehicle. Product temperatures should be checked with an electronic temperature probe and the result recorded for future reference. The loading area should be enclosed and refrigerated, and there should be port doors so the food to be loaded into the transport vehicle/container does not come in contact with the ambient air. Loading may be bulk loading, by machine or manual, of un-packaged foods. It may be manual loading if individual cartons or it may be loading if unitized loads on pallets or slipsheets, using forklifts or pallet jacks. Air circulation. Adequate space for air circulation over and around the cargo is necessary to protect the food products from heat from the outside. For all types of cargo, it is absolutely essential to leave a few centimetres between the floor and the goods. One way of ensuring this is to use a ducted floor.

a. there is not sufficient time for the sensors to measure the correct temperature.

Pre-cooling of the transport equipment is sometimes recommended, see section 1.4 above.

b. the two sensors are not placed sufficiently close c. the calibrated instrument has not been checked recently

Temperature control. The temperature setting should follow recommendations from the carrier, who should be familiar with the equipment, the location of the probe and the systems logic.

The despatch documents should bear a record of product temperature measured

Bracing. The cargo should be secured to prevent vibrations, shifting etc. Shifting

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may block air channels under and through the load. Especially at the end of the last stack in trailers, cross-bracing should be used to prevent the cargo from shifting backwards and blocking air circulation at the rear door. Similarly if a load is consigned to several receivers, cross-bracing should be used at the stack left after each drop off to keep the cargo in place. In road vehicles, the installation of angle irons in the lower corners and the full length between wall and floor is often recommended. This ensures permanent ventilation channels between the side walls and the cargo and also gives greater load stability. Most foodstuffs are loaded on pallets for road transport and the products are often secured to the pallet by protective plastic film wrapping. This technique guarantees that the packaging+pallet assembly keeps a predictable shape. However, the bottom 8 cm of each pallet should be kept free of plastic film to ensure that the correct air circulation at floor level is not prevented. Further information on loading is given in sections 1.5 and 1.6 above. 7.3 Receiving procedures The unloading area should preferably be enclosed and refrigerated, with dock seals at the trailer or container doors (port doors). Receivers should check the load to determine if it meets specifications for quality and packaging. The receiver should also note whether the load was adequately braced and should check the temperature. The air temperature recorder should be read and any other recording devices if

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placed in the load should be studied. If air temperature data is suspect or insignificant product temperatures may be measured, as described in chapter 1 section. Unloaded food products must be protected from direct sun, condensation, contamination, etc. and should be transferred to the relevant storage rooms as soon as possible. Otherwise, the efforts of the manufacturer, shippers and carriers to maintain quality will all have been in vain. 7.4 pre-cooling the foodstuffs Loading cargo without pre-cooling may cause considerable problems, because the product temperatures can not be lowered quickly enough. These problems may be quality degradation or, especially for chilled foods, excessive microbiological growth. Condensation problems may also occur. It can be seen from fig.1.1, the psychrometric chart, that as the temperature drops within the vehicle, water vapour will condense out of the air. A lot of this water will condense on the cold fins of the evaporator coil, forming ice which could restrict the air flow. Condensation may also collect on the cardboard cartons thus weakening the strength of the packaging, but the most damaging problem caused by condensate is that the free water provides good conditions for bacterial growth. The trend for packing foods in plastic overwraps or plastic bags means that, if the food is not pre-cooled to the transport temperature, the subsequent cooling of the packaged food product may result in free water inside the bag, providing a suitable environment for bacterial growth. Cooling time When foods must be cooled prior to transport, the arrangement of the food products (the transport cartons) is very important. If uniform size cartons (600 x 400 x

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250 mm) are cooled in circulating air with a temperature of 0°C and a velocity of 2 m/s, the time to reduce the product temperature from 12°C to 2°C will be about 6 h if the cartons are spread out on, for example a pallet, in a way that circulating cold air will come into contact with all sides of all cartons. If the cartons are placed in a single tier, the cooling time will be 8-10 h. It will take 20 h or more if the cartons are stacked in a block without spacings.

Cooling during transport. Where pre-cooling facilities are not available and the product has to be loaded “hot”, then every precaution should be taken to reduce the product temperatures as quickly as possible. The cooling times mentioned above illustrate clearly that when cooling of foods during transport is unavoidable, it is essential to stow the cartons in such a way that all parts of the cargo are supplied with a sufficient amount of cold air. Dun-

A

B

C

Fig.2.11 Refrigerated vehicle with top-air delivery and a loading pattern providing good air circulation through the cargo. A solid return air bulkhead is installed at the front to prevent air from bypassing the load. The cartons must have sufficient strength to permit this stacking system. In vehicles without T-bar floor or similar construction, pallets should be used. A. Side view showing the continuous air channels constructed in alternate layers. B. End view showing the rear stack. C. Header stack at the front for connecting the horizontal air channels and allowing the air to return to the evaporator.

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nage battens between each layer, and a stowage system as shown in fig. 2.11 should be used, but as stressed several times, refrigeration units in transport equipment are not designed and do not have the capacity to cool down foods at a reasonable or safe rate. Especially at

high ambient temperatures, the cooling will be very slow and there is a considerable risk of quality deterioration and reduction in the remaining storage life. In chilled foods, the risk of bacterial growth possibly of pathogenic organisms - is high.

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3 CHAPTER

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PRACTICAL STORAGE LIFE INTRODUCTION Section 1 describes the processes involved in quality degradation, i.e. the processes limiting the practical storage life (PSL) of foods. Section 2 includes the TTT-PPP concept, i.e. the factors determining quality and storage life of chilled and frozen foods. Calculation of quality loss, or more correctly of remaining PSL is included in section 2.5. Section 2.6 outlines the type of information given in sections 3,4 and 5. Sections 3,4 and 5. More detailed information is given for a number of food products. The most relevant regulations and standards, minimum requirements for the raw materials, processing and packaging, the practical storage life (PSL) at different storage temperatures (in most cases a PSL-diagram), ideal and prescribed transport temperatures, and sensitivity to temperature and odour. The following food product groups are discussed:

Section 3. Deep frozen foods (quick frozen foods) 3.0 Introduction 3.1 Meat 3.2 Poultry 3.3 Fish 3.4 Fruit and fruit juices 3.5 Vegetables 3.6 Miscellaneous Section 4. Frozen foods Meat,poultry,butter

Section 5. Chilled foods 5.0 Introduction 5.1 Retailpacked fresh meat 5.2 Retailpacked meat products 5.3 Meat for further processing (manufacturing meat) 5.4 Poultry 5.5 Fresh (retailpacked ) fish 5.6 Fish products 5.7 Live fish 5.8 Dairy products 5.9 Miscellaneous Definitions and explanations of some terms and expressions may be found in chapter 5.

1. Factors influencing quality processes. During storage (including transport and display), the quality of foods changes gradually, in most cases the quality decreases.A number of factors may be involved. For chilled foods growth of microorganisms is the main factor. Generally the storage life of chilled foods is limited by microorganisms. 1.1 Microbiology. Microorganisms can be divided into three categories, namely thermopfilic, mesophilic and psychrophilic (or more correctly psychrotrophic) organisms. The relative rate of growth depending on storage temperature is shown in figure 3.1.

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Activity Thermophilic bacteria Mesophilic bacteria Psychrotrophic bacteria Mold

Enzymes -40

-20

0

20

40

60

Temperature, °C

Fig.3.1 Growth rate of microorganisms and enzymatic activity, depending on temperature. The figure gives relative activity.

The figure shows that thermophilic and mesophilic bacteria generally grow much faster than do psychrotrophic bacteria and mold. Mesophilic bacteria grow fastest at 30-40°C, and they are killed -except for bacterial spores- at temperatures around 70°C. At temperatures below 10°C, very few mesophilic bacteria are able to grow. At chill temperatures psychrotrophic bacteria, but also mold and yeast are the important microorganisms. The growth of microorganisms depends on temperature, but also on factors such as available nutrients ( the composition of the foodstuff ), aw (water activity, see chapter 5) ,availability of oxygen, and the possible presence of growth inhibitory compounds ( preservatives, a high per-

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centage of carbon dioxide in the atmosphere surrounding the foodstuff). The so-called Hurdle-concept is often used to illustrate the influence of different factors (different hurdles) on the safety and storage life of foods. The importance of availability of oxygen must be stressed, especially for chilled food. Most food spoilage microorganisms are aerobic, i.e. they prefer or demand that the atmosphere surrounding the foodstuff contains a rather high amount of oxygen, e.g. around 20% oxygen. Some microorganisms are useful, for example the types of yeast used in the production of bread, beer and wine. In many vacuumpacked meat products, lactic acid

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bacteria usually becomes the dominant flora. The changes in eating quality resulting from the growth of lactic acid bacteria are rather small. Furthermore, they produce lactic acid which lowers the pH, thus reducing the possibilities of growth of spoilage and pathogenic bacteria. Therefore, lactic acid bacteria are mostly regarded as useful bacteria. The majority of microorganisms are regarded as harmful. The microorganisms may multiply on the food surface, and their main deteriorative effect is to produce unpleasant smelling and tasting compounds, which ultimately make the food inedible. The microorganisms normally involved in food spoilage generally present no health hazard as the changes occuring in the food product are such that nobody will consume it. Food poisoning. Some microorganisms can cause food poisoning without causing noticeable changes in the foodstuff, i.e. the taste and smell will not tell the consumer that the foodstuff may cause illness.

Name of bacteria Clostridium botulinum,type A and B

Some organisms can cause illness if the foodstuff consumed contains a sufficient large number of viable bacteria, often 100000 to 1 million per gram foodstuff. Examples on this type of food poisoning bacteria are Salmonella, Campylobacter, Yersinia enterocolitica and Listeria monocytogenes. The second type of food poisoning organisms produce a toxin in the foodstuff prior to being eaten by the consumer. Examples are Staphylococcus aureus and ,especially, Clostridium botulinum which generally is considered the most dangerous microorganism. Clostridium botulinum is a spore forming bacteria, and spores from Cl.botulinum type A or B may survive heating to above 110°C. Most food poisoning microorganisms are mesopfilic and grow very slowly, or not at all, at temperatures below 10C. During the last years, an increasing number of incidences of food poisoning have been caused by food poisoning bacteria capable of growing at temperatures down to around 0°C, see table 3.1 below.

Minimum temperature 10.0°C

Clostridium botulinum,type E

3.3°C

Listeria monocytogenes

1.0°C

Salmonella typhimurium

5.0°C

Staphylococcus aureus

6.0°C

Yersinia enterocolitica

-0.5°C

Table 3.1 Minimum temperature for growth of some important food poisoning bacteria.

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For chilled foods at temperatures below 0°C, fig. 3.1 shows that mold may grow faster than bacteria. For frozen foods, there is no microbiological growth at temperatures below about -8°C. As shown in fig. 3.1 enzymatic activity continues, even at temperatures as cold as -40°C. A high number of bacteria in foods before freezing may lead to spoilage before completion of the freezing process when the freezing process is not started soon enough, or when the freezing process is too slow. Freezing kills only a few microorganisms, and thawed food products will contain approximately the same number of microorganisms as before freezing. Normally, the storage life (PSL) of a thawed product is approximately the same as that of an unfrozen product. 1.2 Chemical and biochemical processes. Flavour changes. A number of chemical and/or biochemical (enzymatic) processes may proceed in foods during storage, most of them resulting in changes in taste and odour, i.e. a deterioration in the organoleptic (sensoric) quality. The general rule is that decreasing temperature slows down chemical and biochemical processes. Most processes are only known to a limited extent; however, the processes leading to rancidity have been studied in great detail. Rancidity is a phenomenon occuring in fats. To start the process oxygen must be present. Rancidity results in rancid taste and odour, which is unacceptable to many consumers. The fat in foods such as fatty fish is very susceptible to oxidative rancidity, while the fat in for example beef is much less susceptible. Rancidity is the main quality limiting process in many foods, especially in many deep frozen foodstuffs.

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Texture changes. Optimal texture varies from food to food. In meat, poultry and fish, it is the proper degree of tenderness. Cold shortening may cause toughening of meat, see section 3.0 below. For meat, the ageing (also called ripening or maturing) is accompanied by a gradual increase in tenderness. This process takes a few hours in chicken and several days in beef. The ageing time depends on the temperature, and is longer at lower temperatures. Full ageing, at 4°C, may require up to 2 weeks for beef, 1 week for veal, and 4 days for lamb. Texture changes in frozen meat,poultry and fish is caused by protein breakdown, and oxidation seems to have some influence on these protein changes. The increased concentration of salt in deep frozen foods seems to be the main explanation to protein breakdown in these frozen foods. In other foodstuffs different processes may cause texture changes, for example the enzyme pectinesterase may cause “cloud loss” after reconstitution of frozen concentrated orange juice. Colour changes. Any change in appearance from the natural (fresh) character is regarded as a quality defect. In many frozen vegetables, the bright green colour (chlorophyll) becomes more dull and yellow (pheophytin). Proper blanching and proper storage temperature (below -18°C) minimize this quality defect. In frozen fruits, several enzymes may cause degradation of pigments. In meat and especially in beef, the colour is very important. In meat, the main pigment is myoglobin. In traditionally packed chilled meat, myoglobin is found in the

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oxygenated form, oxymyoglobin, which is bright red. Removal of oxygen, for example in vacuumpackages, will result in formation of the purple myoglobin. During storage, myoglobin or oxymyoglobin may be oxidized to the less attractive form of the pigment, brown metmyoglobin.

• Product, i.e. nature and quality of the product at time of chilling/freezing

In cured meats, myoglobin is found as nitrosomyoglobin, and after heating as nitrosohemochrom, see section 5.2 below.

The first two are referred to as TTT (Time-Temperature-Tolerance), while the last three are referred to as the PPP-factors (Product, Process, Packaging).

• Processing during preparation, including the cooling process • Packaging

2. TTT-PPP CONCEPT

The factors affecting the quality of chilled and frozen foods are: • Temperature (Storage temperature) • Time (Storage time)

2.1 TTT. This means that for each product there exists a relationship between storage temperature and storage life. Storage life may be defined in several ways, but here PSL is used (Practical Storage Life), defined as the period where the food pro-

PSL, months 20 18 16 14 12 10 8 6 4 2 °C -30

-20

-10

0

Fig. 3.2 TTT-diagram giving PSL for frozen minced beef at different temperatures. '

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duct retains its characteristic properties and remains fully acceptable. The relationship between storage temperature and storage life is normally given in a TTT-diagram, also referred to as a PSL-diagram, as shown in fig. 3.2. A PSL-diagram shows how the practical storage life (PSL) of the food product depends on storage temperature. As can be seen later, see sections 3,4 and 5, some foods deteriorate rapidly (chilled minced meat), others are less susceptible, and some foods are rather stable (deep frozen beef). PSL-diagrams are used for chilled as well as for frozen foods. In most cases PSL for frozen foods is given in months, while for chilled products it is given in days or weeks. The PPP-factors can be as decisive for product quality as the storage temperature and time. Below the PPP-factors for some chilled and frozen foods are discussed. Generally, the PSL-diagrams give an indication of the PSL at different temperatures, for foods of high initial quality which have been processed and packaged according to good manufacturing practice (GMP) and have been maintained at a reasonably steady storage temperature. 2.2 Product Product means the nature and quality of the raw material before processing. It is well-known that some foods keep longer than others, for example frozen beef keeps longer than frozen fatty fish. It is well-known that a low initial microbial level in the food product and of the raw materials, results in a longer storage life. Meat. At slaughter, glycogen is converted to lactic acid causing a fall in muscle pH from 7

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in the live animal to an ultimate pH of 5.56 in meat, and 5.9-6.4 in poultry. At the same time, the concentration of ATP in the muscles decreases, leading to rigor mortis. Rigor mortis is developed in about 10-30 h for beef, 4-8 h for pigs, and 2-4 h for chicken. DFD. If an animal is exhausted at the time of slaughter, the glycogen reserves are small, and the ultimate pH will be higher than normal. DFD meat has a pH above 6.4, and the meat is dark, firm and dry. The storage life of chilled DFD meat is reduced, especially when vacuumpacked. PSE, (pale, soft and exudative (exuding water)). A very quick fall in pH immediately after slaughter may cause PSE meat, i.e. pale, soft and exudative meat. The problem is confined almost entirely to pigs. PSE meat is of lower quality, with a reduced water binding capacity. Ageing is mentioned in section 1.2 above, and cold shortening in section 3.0 below. Fish and shell fish The term fish (or fishery products) includes fish and shellfish. Shellfish can be further divided in molluscs such as oysters and squids, and crustaceans such as shrimps, crabs and lobsters. For technical reasons, fish is often divided into lean and fatty fish. Fish may come from seawater or freshwater and they can be caught in their natural surroundings or be farmed under controlled circumstances. It is a very diverse group with thousands of species and therefore the products differ greatly. In this book, the term fish (or fishery products) is used for all of the above mentioned groups. The chemical composi-

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INTRODUCTION

zones will mostly be psychrotrophic bacteria such as Pseudomonas, Shewanella and Moraxella. Since they grow well at temperatures below 10°C, lowering the temperature by using ice is of great importance. The deterioration of fish starts after death with degradation of the nucleotides. Later on, bacterial deterioration will take over. Fatty fish will be rancid due to oxidation of the polyunsaturated lipids. All three deterioration processes are temperature dependent. As bacteria on fish from temperate zones are psychrotrophic, their activity is reduced very much by lowering the temperature to 0°C. During chilled storage, Pseudomonas and Shewanella become the dominant bacteria having a high spoilage potential. The guts usually contain many enzymes and bacteria and the storage life is usually lengthened by gutting/evisceration. In fig. 3.3 is shown a typical S-shaped curve for the decrease of the eating quali-

tion of fish varies depending on the species, and in individuals depending on age, sex, season and environment. The composition of a fish fillet is 16-21% protein, 0.2-25% lipid, less than 0.5% carbohydrate and 66-81% water. Marine fish contain trimethylamine oxide (TMAO). Fish lipids contain many long-chain unsaturated fatty acids. The polyunsaturated lipids are considered a good nutrient for humans, but they are very susceptible to oxidation. Fish contains only a small amount of glycogen, and the ultimate pH is 6.2-6.5 compared to 5.5-6.0 in mammalian meat. The high pH in fish flesh is less inhibiting to the bacteria, causing a shorter storage life of chilled fish than of chilled meat. The newly caught fish has many microorganisms on skin, gills and in the guts. They will be transferred to the flesh when the fish is filetted. The type of microorganisms on the fish will depend on the geographical area in which the fish is caught. Bacteria on fish from temperate Quality score 10

8 6

4

2

Days at 0°C 2

4

6

8

10

12

14

Fig. 3.3 The change of quality with time for cod stored at 0°C

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ty of cod stored at 0°C. A change in one of the PPP-factors can increase the storage life; for example the use of vacuum packaging could increase the time until the acceptability limit is exceeded from about 12 days to about 15 days. However, for vacuum packed lean fish the quality decrease during the first 5-7 days will be the same as for non vacuum packed fish as shown in fig. 3.3. After 5-7 days the quality degradation in vacuum packed lean fish will be slowed down, thus increasing the time where the fish is of secondary quality. 2.3 Processing Processing, i.e. the pre-treatment prior to chilled/freezer storage, often influences storage life. Heat processing. Blanching is used in the production of most frozen vegetables in order to inactivate enzymes that otherwise would cause off-taste during storage, even at temperatures below -18°C. Blanching is carried out by heating the vegetables in water at 90-98°C, or in steam at about 100°C, for a relatively short time,usually 1-10 min. Heat processing kills some micro-organisms, depending on time and temperature. When foodstuffs are heat processed, the bacterial number is reduced, and this should increase the storage life. Comminuting, mincing, slicing, etc. increase the surface of the foodstuff, and increase the possibility of unwanted processes, i.e. normally result in a reduced storage life. The freezing process is described in section 3.0,below. The chilling process is described in section 5.0, below. 2.4 Packaging The most common packagings and pack-

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aging materials are described in section 4.1 in chapter 1. The packaging can have a pronounced influence on storage life. For most chilled and frozen foods, the storage life can be increased considerably by using a package with a low WVTR and by preventing oxygen from coming in contact with the food. This is done by vacuum packaging or using MAP, in both cases the packaging materials must have a low or very low permeability to gases, especially oxygen and carbon dioxide. Some of the PSL-diagrams in sections 3,4 and 5 show the influence of different packagings on Practical Storage Life (PSL). 2.5 Calculation of quality loss. Calculation of quality losses, or more correctly of loss of the PSL, is based on the rule of additivity. This rule was developed for frozen foods, in 1950-1960 in USA. The principle is that when the time-temperature history of a product is known, then the quality loss can be calculated, provided sufficient information on the PSL at the relevant storage temperatures. It is assumed that the loss of quality, the loss of remaining PSL, is irreversible and cumulative. For minced beef with a PSL diagram as shown in fig. 3.2, PSL at -24°C is 15 months (450 days) and PSL at -18°C is 10 months (300 days). If this product is stored at -24°C for 90 days and at -18°C for 45 days, the loss of PSL is 90/450 + 45/300= 0.35 (or 35%). Still, 65% remain, i.e. the product could be stored at -18°C for a further 195 days and still be fully acceptable. It can be seen that the sequence ot these two time-temperature episodes do not influence the result. For frozen foods, the rule of additivity is valid except

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INTRODUCTION

• when temperatures become above -8°C, where microbiological growth may occur • at highly fluctuating temperatures that could cause dehydration (frost formation inside the package) or breakdown of emulsions. • for products such as fruits in syrup where temperatures warmer than about -12 to -15°C will cause melting and an unacceptable appearance of a consumer pack.

PSL than if the incorrect temperature occurs later. Thus, it is very important for the quality and storage life (and safety) of chilled foods that the product temperature is kept as low as practicable for as long a time as possible. Although the rule of additivity does not give as accurate results for chilled foods as for frozen foods, calculations on chilled foods will in most cases give reasonably reliable results.

Transport. Similar calculations can be carried out in order to determine the influence of too warm conditions, for example during transport.

2.6 Information given on product groups For each of the product groups included in sections 3, 4 and 5, the following information is given:

Example: If the minced meat product with the PSL diagram shown in fig. 3.2 was transported 10 days at -12°C instead of at the required -18°C, what would be the loss in remaining PSL? At -12°C, PSL of minced beef is 6 months (180 days). 10 days at -12°C is 10/180=0.06 (a loss in PSL of 6%) while 10 days at -18°C is 10/300=0.03 (a loss in PSL of 3%). The incorrect transport would increase the loss in remaining PSL from about 3% to about 6%, a difference so small that it would be impossible to determine by means of analysis.

• Description. This is general information on the foodstuffs included in the product group.

These calculations have been concentrated on frozen foods, mainly because the rule of additivity was developed from experiments with frozen foods. It is generally accepted that such calculations give reasonably accurate results for frozen foods. Chilled foods. The additive rule calculations are not valid for all chilled foods. For some chilled foods storage at too high a temperature in the beginning of the cool chain has a more detrimental effect on the remaining

• Regulations, standards. This mentions the regulations, standards, etc. which are relevant for the foodstuffs in the product group. More detailed information may be found in chapter 1 in section 6. • Minimum requirements. This summarizes the relevant PPP-factors, see sections 2.2 to 2.4. Product, the minimum quality standards of the raw material. Processing, the standards of the manufacturing of the foods. Packaging, the packaging normally used for the product group. • Practical storage life (PSL). This is in most cases depicted in a PSL-diagram, see fig 3.2 in section 2.1 above. Sometimes PSL is given at one or two temperatures, due to lack of relevant data. For the foodstuffs included, a PSL-diagram only provides a very rough guide to their storage potential. To enable a

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prediction to be made of the storage life of a particular product, knowledge of the PPP factors relevant to it is vitally important. • Temperature limits. This comprises: The ideal temperature, i.e. the temperature which should be maintained in the cold chain to give the best quality and the longest PSL of the foods. The limits for transport, set up by ATP and EEC. It should be noted that the ATP-Agreement includes a tolerance (a brief rise of the temperature of the surface of the foodstuff of not more than 3°C above the maximum temperature) for frozen and deep-frozen foods, see chapter 1 section 6.1. The EEC Quick frozen food directive allows a brief rise in the temperature of the foodstuff to -15°C during transport of deep-frozen foodstuffs, see chapter 1 section 6.2. For a few product groups in section 5, the legislative demands in Denmark are included. • Sensitivity. The temperature sensitivity is shown by means of stars (★).

★

means that the foodstuff is relatively robust to temperatures above the required storage and transport temperature. ★★★★★ means that the product must be maintained at the required temperature. Temperature abuses may result in much reduced PSL, or involve considerable risk of (bacterial) food poisoning. For some foodstuffs, the sensitivity towards foreign (off-) odours is given. ★ means little or no sensitivity, while ★★★ shows that the foodstuff easily picks up odour from the surroundings. See also chapter 2 section 1.7.

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A summary is given indicating the effect of incorrect temperature and the products sensitivity to temperature variations.

3. DEEP FROZEN FOODS

3.0 Introduction Deep frozen (quick frozen) foods must be maintained at a temperature of -18°C or lower. The quality degradation processes limiting the storage life of frozen foods are summarized above, see section 1. The PPP-factors are summarized in section 2.2-2.4 above, and here only the freezing process and the thawing process will be discussed. Freezing process. During the freezing process, the product temperature is lowered to below the initial freezing point. At this temperature, ice crystals begin to form. As the temperature is further reduced, more and more water is turned into ice so that the residual solution will become more and more concentrated. A high percentage of water (many foods contain 70-90% of water) is converted into ice as the temperature is brought down to -18°C, but even at -40°C some unfrozen water remains. The freezing process must be started as quickly as practicable, and the speed of the freezing process itself should be adequate. Most experimental data show little or no influence of freezing rate on food quality, when very slow freezing is avoided. However, the widespread view of quick freezing leading to small ice crystals and superior quality is still popular, and is even incorporated in legislation in some countries. The EEC Quick-frozen directive (see chapter 1 section 6.2) states that “.. the zone of maximum crys-

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tallization is crossed as rapidly as possible..”. When freezing food products, there will normally be a pronounced difference between the surface temperature and the centre temperature. After 16 h of blast freezing of hindquarters of beef, the surface temperature could be -32°C and the centre temperature -5°C. After for instance 4 hours of equalization (thermal stabilization) the temperature could be -20°C throughout the product, i.e. the average temperature after 16 h of freezing was -20°C. The freezing process must not be considered as completed until the average temperature has reached the intended storage temperature. However, it is normally recommended to continue the freezing process until the centre temperature is -10°C or colder, and in this case the freezing process should be continued until the centre temperature has dropped from -5°C to -10°C or colder. There is no need to continue the freezing until the centre has reached the intended storage temperature. On the contrary, continued cooling of the product may result in unnecessary low temperatures in the surface layers. This will result in energy waste and inefficient use of freezer capacity, and could in some cases even be harmful to product quality. Freezing time. Freezing time is often defined as the time elapsed from when the product is placed Freezing process Rapid freezing Normal freezing Slow freezing Very slow freezing

in the freezing apparatus until the final product temperature is reached. The freezing time depends on the initial and final temperature of the product, the quantity of heat to be removed, the dimensions (especially the thickness) of the product, the heat transfer coefficient and the temperature of the freezing medium. In packaged foods, the packaging material acts as an insulator and reduces heat transfer. However, packaging in plastic materials will have very little influence on freezing time, unless air is trapped between product and packaging material. If the food products are placed in cartons, especially in corrugated board cartons (see chapter 1 section 4.2.2) the freezing time is increased considerably. Freezing rate or freezing speed. It is not very meaningful to compare freezing times for products of vastly different size, e.g. beef quarters and peas, and hence the concept of freezing rate has been introduced. Freezing rate is normally expressed as the average velocity at which the ice front advances from the food surface to the centre. For practical purposes, an average freezing rate can be defined as the ratio between the minimum distance from the surface to the centre and the freezing time. Freezing time could be the time from the surface reaching 0°C to the centre reaching -10°C. Freezing methods may be characterised by the freezing rate: Freezing rate over 1 cm/h 0.3-1 cm/h 0.1-0.3cm/h less than 0.1 cm/h

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Freezing methods. Freezing equipment must be designed to accommodate the freezing process. Freezers may be divided into four main groups according to the heat transfer medium (freezing medium): • Direct contact. Plate, band freezers. • Air. Air blast freezers. • Liquid. Immersion freezers. • Evaporating liquids/solids. Liquid nitrogen, liquid or solid carbon dioxide freezers. Air blast freezing. Equipment designs vary widely, and among the systems employed are tunnel freezers, belt freezers, and fluidised bed freezers. Tunnel freezers are insulated rooms equipped with evaporator coils and fans. Products of every size and shape, wrapped or unwrapped, can be frozen in the very flexible tunnel freezers. Cold air, often -35°C or colder, is circulated over the food products placed on racks or trolleys. The cold air must have access to all food products, and the air velocity over the foods must be sufficient, i.e. above 23 m/s for packaged foods. An air space should be left between the product layers in order to prevent too slow freezing of the products in the middle of a block. The rate of freezing depends on the dimensions (thickness) and shape of the product, and the overall heat transfer. The heat transfer increases with increasing air velocity, but too high air velocity results in an increased amount of heat produced by the fans. As mentioned above, packaging materials (especially outer cartons made of corrugated board) may considerably increase the freezing time and reduce the freezing rate. The remaining groups of freezers are

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used to a much lesser extent than the air blast freezers. Mobile freezers. A mobile freezer is a trailer or container with a refrigeration unit designed to freeze foodstuffs, i.e. a much higher refrigeration capacity than normally used in transport equipment. The freezing is air blast freezing, and when the mobile freezer is correctly packed, the freezing time for a load can often be reduced considerably as compared to the freezing time necessary for most regular freezing tunnels. This concept ensures the customer of considerable versatility, since the freezer can be positioned where the need is greatest. Thus it is suitable for seasonal goods as well as for foodstuffs from areas where there is a considerable distance between a food processing plant, e.g. a slaughterhouse, and a cold store. Here, the freezing process can be completed during the transport. Thawing. Many food processors use frozen raw materials. Usually, the frozen products must be tempered or thawed before they can be utilised. If thawing is not carried out carefully, quality and yield can suffer. Appearance, microbiology and weight loss are important if the foodstuff is to be sold in the thawed condition, but are less so if it is destined for further processing. Thawing methods may be the conventional surface heating methods or electrical methods (especially microwave thawing). Thawing simply reverses the freezing process and each point in the foodstuff follows the typical highly simplified curve shown in fig. 3.4. The thawing process clearly is divided into three parts: • heating the frozen foodstuff to its thawing plateau. • thawing.

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• heating the foodstuff above its thawing point. The thawing time is the time elapsed from the start of the process to the point where no ice remains in the foodstuff. Surface heating methods are often based on programmed temperature differences between the food surface and the surroundings (the thawing medium), the surroundings starting warmer and becoming colder as the food surface warms up to a predetermined level, often 5-8°C, where there is little risk of bacterial growth and discoloration. Thawing is much more difficult to control than freezing. In some types of air thawing equipment, the air temperature is controlled by means of a temperature sensor, measuring the food surface temperature, but this demands a very ac-

curate positioning of the sensor. The maximum surface temperature is programmed, and when this temperature is reached, the air temperature is reduced to this level. In this manner it is possible to achieve a well controlled thawing process at the highest speed that is practicable. Irrespective of the method used, heat energy must be supplied, most of it being required to melt the ice in the food. About 300 kJ are required to thaw 1 kg of fish with a temperature of -30°C, see Enthalpy below. Since the thermal conductivity of the thawed product is much less than that of the frozen product, conventional thawing methods suffer from the inherent disadvantage that resistance to heat transfer increases progressively once thawing has started.

Temperature, °C

a: Tempering b: Thawing c: Heating

0

a

b

-20

c

Time

Fig. 3.4 Typical, simplified, thawning curve for a foodstuff

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Tempering. Especially in the meat industry, frozen foodstuffs may be processed, for example in choppers, when their temperature has been raised to about -4°C. The process is called tempering, i.e. the initial phase of a complete thawing process. Tempering is process a. in fig. 3.4 above. Tempering can be done by means of microwaves, thus obtaining a very rapid process. The use of microwaves for complete thawing is constrained by thermal instability. At its worst, parts of the food may be cooked whilst the rest remains frozen. This arises because the absorption of microwave energy increases as the temperature increases. If a region of the foodstuff becomes slightly hotter than its surroundings, proportionately more energy will be absorbed within that region, increasing the temperature difference between that region and its surroundings. This is often called runaway heating. Runaway heating can be reduced by increasing the thawing time, e.g. by allowing some time during the process for temperature equalization. However, this will demand so much time that the main advantage by microwave thawing disappears. Specific heat and enthalpy. The specific heat for water is 4.19 kJ/kgxC (1kCal/kgxC), i.e. to change the tempera-

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ture of 1 kg water 1°C, it is necessary to remove or add 4.19 kJ. For ice, it is about 1.81 kJ/kgxC (0.45 kCal/kgxC). As most foods contain large amounts of water, the specific heat for food products will be rather close to that of water or ice, i.e. 6580% of that of water or ice. The specific heat of foods is comparatively constant at temperatures warmer than the freezing point of the foodstuff or colder than -18°C, but during the freezing process, the specific heat is not constant. The reason is the amount of energy necessary to freeze water (or to melt ice), the so-called latent heat, the energy required to change from a solid to a liquid. Enthalpy. This has led to the use of the total heat content (enthalpy). Several tables exist in which the enthalpy (kJ or kCal) can be seen at different temperatures. For example, the enthalpy of lean fish, e.g. cod with 80% water, is 20.5 kJ/kg at -30°C, 41.8 kJ/kg at -20°C, 74.1 kJ/kg at -10°C, 322.8 kJ/kg at 0°C, and 361.1 kJ/kg at 10°C. Thus, the enthalpy change for lean fish from -30°C to 0°C is about 300 kJ/kg. Enthalpy change is a determining factor in the dimensioning and design of both freezing and thawing equipment.

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3.1 DEEP FROZEN MEAT Description Deep frozen meat (often called quick frozen meat) may be beef, veal, pork, lamb, game, etc. Meat is produced and consumed in all parts of the world, and transport of meat is a very large part of temperature controlled transport of foodstuffs.

directive and the Labelling directive also applies. The EEC directives are summarized in section 6.2 in chapter 1.

Meat is produced and marketed in a number of ways: Frozen minced (comminuted) meat, including hamburgers etc. Frozen retail cuts. Frozen manufacturing meat (primal cuts, pieces, carcasses).

Minimum requirements Raw materials For meat the main quality parameters are appearance (colour), texture, taste, and juiciness. It is absolutely necessary that meat has an acceptable tenderness. Therefore, cold shortening during chilling must not occur, and appropriate ageing must be secured. However, aged meat should not be used for the manufacture of minced meat.

Regulations,Standards. In the EEC States the meat must be produced according to the Fresh meat directive, the Minced meat directive or the Meat products directive. The Quick-Frozen food

Raw materials used in the manufacture of deep frozen foods must be of good and sound quality and be of the required degree of freshness. As mentioned above, the freezing pro-

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cess should be started without undue delay, and be as rapid as is practical. After thermal stabilization (equalization) the temperature of the product should be maintained at -18°C at all points. Packaging. For frozen meat, an appropriate packaging should be used in order to reduce quality losses, especially to reduce weight losses. The packaging should be a tight fitting plastic material with a low WVTR. For meats susceptible to oxidation, leading to for example rancidity in pork with its high percentage of unsaturated fat, the oxygen permeability should be low or very low. Vacuumpackaging is often used for retail cuts and steaks, and for primal cuts; it is sometimes used for minced meat.

Carcasses are often stored and transported unwrapped. However, an increasing number of carcasses are enclosed in stockinettes or plastic packed, for example shrink-wrapping in a suitable plastic material. Meat patties, e.g. hamburgers, are sometimes packed in paperboard cartons with or without an inner plastic coating. This type of packaging should not be used when the intended PSL is more than a few months, as meat patties packed this way easily suffer dehydration and freezer burn. Practical Storage Life ( PSL ). The PSL curves shown in the diagram below are typical, and as mentioned before the PPP-factors influence PSL very much. Fig. 3.2 above shows a PSL-diagram for frozen minced beef.

PSL, months

Lamb Steaks

20 Beef Steaks

15

Pork Cuts

10

5

°C -30

-20

-10

PSL-diagram for some types of retail packed frozen meat

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Temperature limits Ideal temperature: -25°C or colder Legal requirements for transport: ATP: -18°C or colder Tolerance: -15°C for short periods EEC: -18°C or colder Tolerance: -15°C for short periods Sensitivity temperature.

odour.

Retail packed minced beef

★★★

★★

Retail packed pork

★★★

★

Retail packed beef,lamb

★

★

Manufacturing meat

★

★

Odour. As mentioned in section 1.7 in chapter 2, fresh meat readily absorbs odour from food products with a strong odour such as fish, apples, etc. This also applies to frozen meat, although the transfer of odour is much slower at -18°C than at about 3-5°C. Temperature. During transport, a temperature of -12°C for 10 days will give a minor reduction of the remaining PSL, for minced beef only

about 6%, see the example in section 2.5 above. Product temperatures up to -8°C can not cause microbiological problems, and as transport times generally are restricted to days or weeks, the quality degradation of frozen meat will normally be negligible. In practice, as long as the meat is still frozen, i.e. the meat temperature is below -2°C, the quality will normally be only marginally affected by temperature abuses, on condition that the transport time is less than a few days.

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3.2 DEEP FROZEN POULTRY Description Domestic poultry, e.g. chickens, hens, cocks, turkeys, ducks, guinea fowl and geese are very frequently preserved by freezing. Poultry is eaten in all parts of the world, and is generally regarded as a highly acceptable and nutritious foodstuff, with a high protein and a low fat content. Regulations,Standards In the EEC directive 71/118 with several further amendments, the requirements for water chilling of poultry are laid down. It is prescribed that counter-current chillers must be used, that the temperature of the inlet water must be below 4°C and of the exit water below 16°C, that spray cleaning before chilling must be used, with prescribed amounts of water per carcass , that the water pick-up during processing must be below certain limits, etc.

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The EEC Quick frozen food directive and Labelling directive must be followed in the EEC countries. The EEC directives are summarized in section 6.2 in chapter 1. Minimum requirements Raw materials The feeding of, for example, chickens with even small amounts of feeds containing unsaturated fatty acids ( from fatty fish) may result in an early onset of rancidity. Slaughtering, including scalding, plucking, evisceration and chilling must be carried out hygienically and according to good manufacturing practice(GMP) and the relevant regulations. For whole turkeys an ageing period between chilling and freezing (12-24 h at about 0°C) or after freezer storage gives more tender meat. For smaller birds such as chickens, an ageing period (2-4 h) be-

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DEEP FROZEN POULTRY

tween chilling and freezing may give some improvement in tenderness. Broilers, turkeys and ducks are often cut into portions, resulting in additional surface area being exposed to air. PSL of cut-up poultry is somewhat shorter than that of the whole bird due to additional handling and contamination. Pre-cooked poultry or poultry parts are mentioned in section 3.6 below. Packaging. Whole chickens are generally packed

after the chilling process, but before freezing, in rather thin plastic (PE) bags, closed with a clamp. Such packaging materials may result in damage to the plastic in the freezer chain and may cause white spots due to local dehydration, see section 3.2 in chapter 1. Turkeys and ducks are generally vacuumpacked or shrinkpacked in more expensive plastic materials with low WVTR and low oxygen permeability. Turkeys especially demand good packaging because of the tendency for turkey meat to become rancid more quickly than other poultry.

PSL, months

25

Chicken, Whole

20

15

10

Ducks, Geese

Chicken parts/cuts, vac. pack. Chicken parts, normal packaging

5

°C -30

-20

-10

0

PSL-diagram for some types of retail packed frozen poultry

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DEEP FROZEN POULTRY

Temperature limits Ideal temperature: -24°C or colder Legal requirements for transport: ATP: -18°C or colder Tolerance: -15°C for short periods EEC: -18°C or colder Tolerance: -15°C for short periods Sensitivity

Whole chickens Chicken parts Turkey

Temperature. Deep frozen poultry, and especially chicken, is a rather robust product with long PSL. When the temperature is -8°C or

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temperature

odour

★

★

★★

★

★★★

★

colder, the influence on quality and remaining PSL is small for normal transport, lasting less than 1-3 weeks, see section 2.5 above.

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FISH

3.3 FISH Description Almost all the groups of fish and fish products mentioned in section 2.2 above and in sections 5.5 and 5.6 below, are marketed and transported in the deepfrozen as well as in the chilled state. Fish that has to be transported at sea over a long distance, is often quick-frozen aboard the ships which means that frozen fish and fish products can be of better quality and be more “fresh” than similar chilled fish after some days on ice. In Japan, fish is often consumed raw, and in order to secure an optimal quality, storage temperatures as cold as -50°C are used onboard the fishing boats. Regulations,Standards In the EEC, the Quick-frozen food directive and the Labelling directive are the most relevant. These directives are sum-

marized in section 6.2 in chapter 1. Codex Alimentarius has issued an international code of practice for frozen fish, where storage and transport at -29°C or colder is recommended. It also states that the freezing process should not be regarded as complete unless and until the centre temperature has reached -18°C or colder after thermal stabilization. In the Codex standards for quick frozen shrimps or prawns, the determination of net content of the products covered by glaze is described. Codex Alimentarius has issued Recommended International Standards for the following quick (deep) frozen fishery products: Gutted Pacific Salmon, Cod and Haddock fillets, Ocean Perch fillets, Flat Fish fillets, Shrimps and Prawns, Hake fillets, and Lobsters.

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FISH

Minimum requirements Raw material. The fish should be of good quality and of the desired degree of freshness, i.e. newly caught and/or chilled quickly to and maintained at 0°C, i.e. the temperature of melting ice. Frozen fish has a shorter PSL than frozen meat. As mentioned in section 2.2 above, fish contain a higher proportion of polyunsaturated lipids which are susceptible to oxidation, and marine fish contain TMAO which can be degraded to dimethylamine (DMA) and formaldehyde (FA). The degradation compounds from oxidized lipids and TMAO can give off-flavours and off-odours, but they can also cause breakdown of the proteins. This breakdown

brings about loss of water and a change in texture. In fatty fish, a considerable amount of free fatty acids can be formed. Processes such as filetting, breading etc. must be carried out according to the above mentioned Codex documents and/or the Codex documents referred to in section 5.5 below. Packaging. Low storage temperatures slow down the degradation, and so does good packaging. The packaging must be tight fitting and must have a low WVTR, as the surface of fish easily suffers freezer burn. For fatty fish it is especially necessary to use a packaging material with a low oxygen permeability, and vacuumpackaging is preferred.

PSL, months 20

15

10

Lean fish 5 Fatty fish, glazed Herring -30

-20

°C -10

PSL-diagram for some types of retail packed frozen fish

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0

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FISH

The fish can also be protected by glazing, i.e. a cover of ice on the surface, which reduces oxidation and dehydration. Glazing is commonly used for whole gutted fish (e.g. Salmon), shrimps (especially

IQF, i.e. Individually Quick Frozen), and blocks of fish or fillets. After some months, much of the glaze has evaporated and the product must be reglazed.

Temperature limits Ideal temperature: -29°C or colder, especially for fatty fish Legal requirement for transport: ATP: -18°C or colder Tolerance: -15°C for short periods EEC: -18°C or colder Tolerance: -15°C for short periods Sensitivity Temperature Fatty fish

★★★

Lean fish

★★

Shrimps

★★★★

Temperature. When the wrong temperature or a fluctuating temperature occurs, the quality loss is increased and the remaining storage life reduced. However, as long as the temperature is below about -8°C, no bacterial growth can take place. Thus,it is possible to calculate the loss of quality and of remaining storage life caus-

ed by, for example, transport at temperatures warmer than prescribed by using the method described in section 2.5 above. It must be stressed that most frozen fishery products have a rather short PSL which makes it essential to maintain the required temperatures throughout the freezer chain.

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FRUITS AND CONCENTRATED JUICE

3.4 FRUITS AND CONCENTRATED JUICE Description Fruits are frozen whole, as halves or slices, with sugar and/or syrup, and as juices or concentrated juices. Most frozen fruit is used for further processing, into jams, marmalades, fruit pulps, fruit juices, fruit yoghurts, etc. Many fruits, e.g. apples, oranges, etc. are normally consumed raw, and freezing is not suitable for such fruits, as they will lose their characteristic texture when thawed. Regulations,Standards Except from the general food laws, little legislation deals with deep frozen fruits. Of course, the EEC Quick-frozen food directive and the Labelling directive must be followed in the EEC countries. These directives are summarized in section 6.2 in chapter 1.

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Codex Alimentarius have issued recommended international standards for the following quick frozen fruits: Strawberries, raspberries, peaches, bilberries and blueberries. Minimum requirements Raw materials The raw materials, the fruits, should be clean and sound, and with no fungal growth. The desired properties of fruits differ considerably between the various industries that use these products. For production of jams it is preferable to use fruit with a firm consistency, which is retained after freezing and cooking. For fruit juices, fruit flavours, etc. it is preferable to use fruits with a full aroma and an intense colour. Especially for strawberries, the same variety seldom possess both firm consistency and good aroma. For direct consumption, only varieties of strawberries with a firm

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FRUITS AND CONCENTRATED JUICE

flesh which retain as much of the original texture as possible should be frozen. Fruits for freezing must be clean and sound. The degree of ripeness at harvest has a marked influence on the quality of the frozen product. Prematurely harvested fruits lack flavour and colour. Fruits picked too late are soft and prone to crushing and fungal attack. Fruits should be cooled between harvest and freezing, unless the time can be kept very short. Processing. Peeling, stoning, slicing etc. are nearly always performed mechanically. Blanching is rarely applied to fruits. The freezing process should be as rapid as practicable. However, fruits when thawed are softer in consistency than the fresh equivalent, even using the fastest freezing method. The benefits of fast

freezing are small when compared with the selection of the best varieties. Packaging. Fruits may be packed before freezing, e.g. fruits in sugar, fruits in syrups, concentrates etc. Whole fruits or individual frozen pieces are packaged after freezing. Frozen concentrated fruit juice is sometimes bulk packed and transported in plywood containers with inner plastic liners, containing up to two tons. The load ing of such heavy containers into the transport equipment demands special attention. Concentrated juice is also transported in US steel drums (55 A.G.). and even 20,000 litre refrigerated ISO tank containers. Retail packaging is done later on, for example in composite cans (cans made of paper with plastic linings).

PSL, months 30

25

20

15

Fruit juice concentrate

10

5

Raspberries (bulk packed, no sugar)

Peaches, retail, syrup

Raspberries, retail, syrup °C -30

-20

-10

0

PSL-diagram for some frozen fruit products

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FRUITS AND CONCENTRATED JUICE

Temperature limits Ideal temperature: -18°C or colder Legal requirements for transport: ATP: -18°C or colder Tolerance: -15°C for short periods EEC: -18°C or colder Tolerance: -15°C for short periods In the ATP, Annex 2, it is stated that deep frozen concentrated fruit juice, when intended for immediate further processing at destination, may be permitted to gradually rise in temperature during carriage so as to arrive at destination at temperatures no higher than those specified by the sender and indicated in the transport con-

tract. The transport document must state that further processing of the concentrated fruit juice is to be carried out immediately on arrival at its destination. This carriage should be undertaken with ATP-approved equipment without use of the thermal appliance to increase the temperature of the foodstuff.

Sensitivity Temperature Deep frozen fruits without sugar Deep frozen fruits in syrup Deep frozen conc. fruit juice

Temperature. For retail packed deep frozen fruits in syrup it is absolutely essential to maintain the product temperature below about -15°C, in order to prevent melting which results in an unacceptable appearance of consumer packs. For most other deep frozen fruits and fruit

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★★ ★★★★ ★

products, temperature abuses during transport normally have a limited influence on product quality as can be calculated using the method described in section 2.5 above. Due to the rather low pH of most fruits, microbiological growth is seldom a problem, even at temperatures rising to the freezing point of fruit products.

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VEGETABLES

3.5 VEGETABLES Description Vegetables cover a large number of varieties. Vegetables such as peas, spinach, French beans, Brussels sprouts, cauliflower, etc, can be successfully frozen. Salad vegetables, for example tomatoes, lettuce and cucumber, which are normally consumed raw, lose their characteristic crisp texture when thawed.

Regulations,Standards In the EEC countries, the Quick frozen food directive and the Labelling directive must be followed. These directives are summarized in section 6.2 in chapter 1. Recommended international Codex standards have been issued for the following quick frozen vegetables: Peas, spinach, leek, broccoli, cauliflower, Brussels sprouts, green beans, French fried potatoes and whole kernel corn.

Minimum requirements Raw materials Only material which is clean, sound and of high quality should be frozen. Some varieties (cultivars) are better suited for freezing than others. The intensely coloured and highly flavoured varieties should be selected for freezing. The vegetables must be able to withstand mechanical harvesting. It is essential to harvest vegetables at the ideal moment of maturity. This optimum period may last a few hours for peas, but 2-3 days for French beans. The period between harvesting and freezing must be short, and the most susceptible varieties must be frozen 2-4 hours after harvesting. Packaging. After freezing (often fluid bed freezing) many vegetables are bulk packed, e.g. in PE-lined pallet boxes which can contain

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VEGETABLES

several hundred kilos of product or in PEcoated paper sacs containing 30 kg. Repackaging into consumer packs can then be carried out according to market demands. Deep frozen vegetables are usually packed in heat sealed plastic materials, e.g. PE pouches. Some companies use

more sophisticated packagings such as alufoil laminates with a very low permeability, thereby reducing the rate of quality degrading processes and increasing PSL. Vegetables such as spinach are usually packed in consumer packs (cartons) before the freezing process.

PSL, months

25

20

Cauliflower

Peas

15

10

Brussels sprouts

5

Aspargus °C -30

-20

-10

PSL-diagram for some retail packed frozen vegetables

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0

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VEGETABLES

Temperature limits Ideal temperature: -18°C or colder Legal requirements for transport: ATP: -18°C or colder Tolerance: -15°C for short periods EEC: -18°C or colder Tolerance: -15°C for short period Sensitivity Temperature Deep frozen vegetables in general Deep frozen asparagus, cauliflower, etc.

Temperature. Most deep frozen vegetables have a very long storage life, and in most cases temperature abuses during transport will only result in a minor decrease in quality and remaining PSL. The loss in quality and

★ ★★★

remaining storage life can be calculated as shown in section 2.5 above. Microbiological problems are seldom seen in deep frozen vegetables when the temperature is kept below -2°C, (for a limited period of time of course).

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MISCELLANEOUS DEEP FROZEN FOODS

3.6 MISCELLENANEOUS DEEP FROZEN FOODS Description Several other groups of foodstuff are frozen commercially, e.g. bakery and confectionary products, ice cream, desserts, eggs and egg products, prepared meals, etc.

Regulations,Standards The relevant regulations depends very much on the product. If a prepared meal contains meat, the controlling authorities in several countries regard the meal as a meat product, and similar rules are valid for several other food products. In the EEC, the Quick frozen food directive and the Labelling directive are valid for all consumer packed deep frozen foods. These directives are summarized in section 6.2 in chapter 1.

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Minimum requirement Raw materials The requirements depend on the product, but in any case the raw materials should be of normal and satisfactory quality, and the processing should be carried out according to good manufacturing practice, GMP.

Packaging. The packaging must protect the food product against dehydration and oxidation. For products which are not sensitive to oxidation, packaging materials with a rather high gas permeability may give sufficient protection. For food products sensitive to oxidation, packaging materials with low or very low oxygen permeability must be used, and vacuum packaging or similar packaging techniques should be applied.

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MISCELNANEOUS DEEP FROZEN FOODS

Practical Storage Life (PSL). The PSL-diagram below indicates the storage life at different temperatures for a few deep frozen products not included in sections 3.1 to 3.5. As is the case for

most frozen foods, the storage life depends very much on the PPP-factors and cannot be predicted without knowledge to these factors.

PSL, months 25

20

15 Cakes French fries (potato chips)

10 Ice cream

5

°C -30

-20

-10

0

PSL-diagram for some retail packed frozen foodstuffs

Temperature limits Ideal temperature: -18°C or colder Legal requirements for transport: ATP: ice cream -20 °C or colder Tolerance: -17 °C for short periods ATP: all other deep frozen foodstuffs -18°C or colder Tolerance: -15°C for short periods EEC: deep frozen foodstuffs -18°C or colder Tolerance: -15°C for short periods

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MISCELLANEOUS DEEP FROZEN FOODS

Sensitivity For this group of deep frozen products it is not possible to indicate the sensitivity to temperatures warmer than -18°C. simply because of the great variation between the different foodstuffs.

Problems with microbiological growth do not exist as long as the product temperature is below -8°C, or as long as higher product temperatures (for example -2°C) are only experienced for a day or perhaps two.

Temperature. As is the case for most deep frozen foods, the loss of quality and remaining storage life can be calculated when the time-temperature history is known. The principle is outlined in section 2.5 above, where it also indicates which type of frozen foods the rule of additivity may not be valid.

As is indicated in the PSL-diagram, some foods are very sensitive to temperature abuses. For ice cream, PSL becomes very short at temperatures warmer than -18°C, and it is often recommended to store and transport ice cream and similar products at -20°C or below, and to display these foodstuffs in special display cabinets in the supermarkets.

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FROZEN FOODS

4. FROZEN FOODS Description Frozen foods comprise foodstuffs which are stored and marketed at temperatures between -12°C and -18°C. The name for this group is “congele” in France and “gefroren” in Germany. The three traditional frozen products are meat, (especially beef and chicken) and butter. These three foodstuffs are robust, i.e. characterized by having a long PSL. Most countries allow the marketing of retail packed frozen foods at -12°C but several countries do not, these demand -18°C for all deep frozen foodstuffs.

Regulations,Standards The EEC Quick frozen food directive does not apply to frozen foods. Several EEC directives include the storage and transport requirements (-12°C or colder) for frozen products (frozen meat, frozen poultry), see section 6.2 in chapter 1.

In the EEC countries, the Labelling directive also applies if the frozen products are destined for the retail market. Minimum requirements Raw materials The requirements for the raw materials are as for deep frozen foodstuffs, see for example sections 3.1 and 3.2 above. In the Fresh meat directive (see section 6.2 in chapter 1), it is stated that the freezing process for frozen foods does not have to be as rapid as for deep frozen foodstuffs. The cream for butter making must be pasteurized, preferably at temperatures above 90°C, to inactivate enzymes and to reduce the number of microorganisms which would otherwise cause quality loss. Only fresh butter, no older than 14 days, of high quality, is suitable for freezing. The storage life depends upon the butter

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FROZEN FOODS

type (sweet cream or cultured, salted or unsalted), the pH, the content of copper, the water distribution through the butter, the salt content and the storage temperature. Packaging. The packaging must protect the foodstuff against contamination, dehydration etc. and must be sufficiently strong to cope with the conditions in the cold chain. Thus, the requirements are the same as for packaging of deep frozen foodstuffs, see for instance section 3.2 above. During freezer storage butter deteriorates mainly by oxidation, but it is also essential to avoid dehydration. Aluminium foil lami-

nates are often used for the packaging of butter in retail packs. Practical Storage Life ( PSL ). The practical storage life of frozen beef can be seen in section 3.1, and for frozen chickens in section 3.2, above. The PSL-diagram for butter shows the great importance of pH and salt content. Sweet cream butter (pH 6.6) has a long PSL whether salted or unsalted. For cultured (also called ripened or fermented) the difference between salted and unsalted is significant: Salted cultured butter has a rather short PSL, but unsalted cultured butter has a reasonable PSL.

PSL, mothns

25

20 Sweet cream, salted pH = 6.6 15

Cultured, unsalted pH = 4.7

10 Cultured, salted pH = 4.7

5

°C -30

-20

PSL-diagram for different types of frozen butter

112

-10

0

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FROZEN FOODS

Temperature limits Ideal temperature: -20°C or colder Legal requirements for transport: ATP, frozen poultry,meat etc. -12°C or colder ATP, frozen butter -10°C or colder EEC, frozen foods -12°C or colder In the ATP, Annex 2, it is stated that butter, when intended for immediate further processing at destination, may be permitted to gradually rise in temperature during carriage so as to arrive at destination at temperatures no higher than those specified by the sender and indicated in the transport contract. This temperature must not be higher than 10°C. The transport docu-

Tolerance: -9°C for short periods Tolerance: -7°C for short periods.

mentation shall state the name of the foodstuff, whether it is deep frozen or frozen and that it is to be further processed immediately at destination. This carriage should be undertaken with ATP-approved equipment without use of the thermal appliance to increase the temperature of the foodstuff.

Sensitivity Temperature

Odour

Beef

★

★

Chicken

★

★

Butter

★

★★★

Temperature. As mentioned earlier, see for example section 3.1 above, these frozen foods are very robust, and could withstand rather severe temperature abuses as long as the temperature violations are restricted to a few days. The loss of quality and remaining storage life can be calculated as described in section 2.5 above. In practice there are no microbiological

problems caused by transport temperatures when the temperature is maintained below -8°C. Odour. Beef, and especially butter, easily pick up odour from the surroundings, for example from other foodstuffs, see section 1.7 in chapter 2.

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CHILLED FOODS

5. CHILLED FOODS. 5.0 INTRODUCTION. Chilled foods must be maintained at temperatures between about -1.5°C and about +5°C. For some chilled foods or in some countries, higher temperatures, for example 8°C, may be allowed. For some chilled foods, an upper maximum temperatures of 2°C or 3°C may be prescribed.

The chilling process. For most chilled foods the temperature should be reduced to the intended storage temperature as quickly as practicable. As the chilling medium usually is considerably colder than the foodstuffs, there will normally be a pronounced temperature difference between the surface and the centre during the chilling process. After 4 hours of air blast chilling at -10°C, the surface of pork sides could be -1.5°C, the centre +18°C, and the average temperature +5°C. If the intended storage temperature is 5°C, there is no need to continue the chilling until the centre is 5°C. The air temperature could be changed to about 5°C, or the pork sides could be transferred to an equilibrium room, again with an air temperature of 4-5°C. The specific heat or the enthalpy change is used for dimensioning and designing the chilling equipment, see section 3.0 above. The chilling process used is very often air chilling, i.e. chilling by cold circulating air. The lower the air temperature, the more rapid the temperature of the foodstuff is reduced to the desired level. However, the air temperature used depends on the food type. For some foods, circulating cold air as low as -25°C is used, but for other foods it is important that no part of the

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foodstuff should suffer freezing, i.e. the circulating cold air should not be colder than -2°C. For fruits, poultry, etc. hydro-cooling, i.e. chilling by cold circulating water, is often used. The most common , and best, means of chilling fresh fish and shell fish is to use ice made from fresh clean water, refrigerated sea water (RSW) or chilled sea water, (CSW). Chilling by means of refrigerated sea water or chilled sea water involves the total immersion of the fish in a tank. These two methods offer considerable advantages particularly on board fishing vessels. The sea water, which must be fresh and clean, can be kept at 0°C to -1°C by means of a mechanical refrigeration system or by adding ice. The water should be circulated in the tank. A substantial extension of storage life can be obtained for many types of fish (especially fat fish), by bubbling gaseous carbon dioxide through the tank. Vacuum-chilling is used for some foodstuffs, e.g. leafy vegetables, as it is a very rapid chilling method. Cold shortening. Lowering the temperature of a hot carcase too rapidly, especially beef, veal and lamb, may result in severe contraction of the muscle fibres, a phenomenon known as “cold shortening”. This is an irreversible process which may cause considerable toughness in the meat. The temperature in any part of beef, veal or lamb should not be permitted to fall below 10°C within 10 hours of slaughter. For pork, chickens etc. a very rapid chilling process may result in a certain toughening, but for these foods ageing seems to improve texture.

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CHILLED FRESH MEAT, RETAIL PACKED

5.1 CHILLED FRESH MEAT, RETAIL PACKED. Description. The meat may be beef, veal, pork, lamb, etc. It may be comminuted (minced), or in small pieces (less than 100 grammes), or in the form of retail cuts. The main quality parameters are taste, texture and juiciness, but above all the appearance and colour (especially for beef). In most cases, the consumers choose meat and meat products from the appearance and the colour of the packaged meat in the supermarket display cabinet. Regulations,standards. In the EEC, the following directives are the most important: The Fresh meat directive, the Minced meat directive, and the Labelling directive. These directives are summarized in section 6.2 in chapter 1.

Minimum requirements. Raw Materials The meat must be of good and sound quality prior to the chilling process. The chilling process must be started as quickly as practicable , and the chilling must be sufficiently rapid to ensure minimum weight loss and no growth of microorganisms, but not be so rapid as to result in toughening of the meat due to cold shortening, see above. Packaging. In conventional retail packs, meat is placed on a tray made of plastic or woodpulp, and then overwrapped with a highly gas permeable plastic material which allows an almost unrestricted supply of oxygen to the pigment (myoglobin), responsible for the meat colour. These conditions favour formation of the bright red colour (oxymyoglobin) which most con-

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CHILLED FRESH MEAT, RETAIL PACKED

sumers associate with freshness and good eating quality. The oxymyoglobin is stable for only 1-3 days in normal display. For fresh beef, vacuum packaging will result in a reduced oxygen level inside the bag and the colour changes to purple, a colour which most consumers are not familiar with. Vacuumpackaging results in a considerably increased PSL, see the PSL diagram. For vacuum-packed beef, pH is a very important factor, and meat with a pH of less than 5.9 is preferred to avoid storage life problems. The-PSL diagram shows that the storage life of minced beef in conventional packaging is so short that it cannot be transported over long distances.

MAP (Modified Atmosphere Packaging) is used to some extent. The meat is placed in a tray with a volume about 2-3 times the volume of the meat. The air is drawn out and replaced with a gas mixture which often contains about 80% oxygen (maintains the bright red colour) and 20% carbon dioxide (reduces the growth of bacteria). The improvement in storage life can be seen in the PSL diagram. Masterpacks are used to some extent, see section 4.1.3 in chapter 1. The resulting PSL is about the same as for MAP meat. CAPTECH is a special form of masterpack, where 100% CO2 is used, and where it is absolutely necessary that no oxygen comes into the package, i.e. it is necessary to use alufoil-laminates.

PSL, days

35

30

25

Meat cuts, vacuum packed

20

15

10

Pork cuts, conv.

Minced beef, MAP

5

Minced beef, conv. 0

°C 5

PSL-diagram for some types of retail packed chilled meat

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CHILLED FRESH MEAT, RETAIL PACKED

Temperature limits. Ideal temperature: -1.5°C Legal requirements for transport: ATP, minced meat max 3°C EEC, minced meat max 2°C ATP, cuts/steaks max 7°C EEC, cuts/steaks max 7°C Sensitivity Product

Temperature

Odour

Minced meat, conventionally packed

★★★

★★

Cuts/steaks, conventionally packed

★★

★★

Minced meat, MAP

★★★★

★★

Cuts/steaks, MAP

★★★

★★

Temperature Temperatures above those recommended or prescribed will increase the growth rate of microorganism and lead to spoilage. Food poisoning is usually no problem in conventionally packed fresh meat as spoilage will turn the meat unacceptable long before food poisoning is possible. For vacuumpacked meat there seems to be a limited risk, but for MAP meat there is a greater risk and here it is absolutely necessary to maintain low temperatures throughout the chill chain. For MAP meat, it is often recommended or laid down in legislation that the temperature of the meat should be maintained below 2°C or 3°C.

Calculation of loss of quality or remaining storage life can be carried out according to section 2.5 above. However, for several chilled meats such calculations do not give very precise results, as warm storage in the beginning of the chill chain reduces quality and remaining storage life significantly more than would be found in such calculations.

Odour As mentioned before, see section 1.7 in chapter 2, fresh meat easily picks up odour from the surroundings. This is especially important for meat in conventional retail packs where the plastic overwrap has a high permeability.

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CHILLED MEAT PRODUCTS, RETAIL PACKED

5.2 CHILLED MEAT PRODUCTS, RETAIL PACKED Description This group consists of a variety of meat products, defined in the EEC as products prepared from or with meat which has undergone a treatment such that the cut surface no longer shows the characteristics of fresh meat. The treatment can be heating, curing or drying, or a combination of these processes. 1Meat products usually have a longer storage life than fresh meat. Regulations,Standards In the EEC, the Meat products directive, and the Labelling directive are the most relevant. These directives are summarized in section 6.2 in chapter 1. Minimum requirements Raw materials. The meat must have a good and sound

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quality, and be of the desired degree of freshness. The processing must be carried out according to good manufacturing practice, and the temperature during processing should be below 20°C or above 50°C. The resulting PSL depends on the composition of the product (for instance the salt/water ratio), the initial bacteriological quality (total count and composition of the bacterial flora), the time and temperature of a possible heat processing, etc. The meat products should be chilled as quickly as practicable, preferably to 0°C or even colder. The initial freezing point for many cured meat products is about -3°C to -4°C, and such products would benefit from storage and transport at temperature around -2°C (deep chilling). Meat products are often sliced, and to achieve a good initial bacteriological quality the slicing process must be carried out

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hygienically , which involves frequent and adequate cleaning and disinfection of machinery, conveyors, tables etc.

the oxygen content must be less than about 0.3%, and a commonly used mixture is 60% nitrogen and 40% carbon dioxide.

Packaging. The pigment in cured meat is nitrosomyoglobin, which after heat processing is transformed into nitrosohemochrom. Both pigments fade rather quickly if the meat product is in contact with oxygen. Therefore, vacuumpackaging or MAP is generally used to obtain the required PSL. In MAP,

Practical storage life (PSL) The PSL-diagram below indicates the storage life of vacuum packed sliced cured meat products. PSL of meat products depend very much of the initial bacterial state, the processing and the packaging (the so-called PPP-factors, see section 2 above).

PSL, weeks

20

15 Cooked pork loin, sliced, vac.packed 10

5 Bologna-type sausage, sliced, vac. packed °C -5

0

5

10

PSL-diagram for two types of retail packed cured meat products

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Temperature limits Ideal temperature: -2°C (depending on initial freezing point) Legislative demands for transport ATP: max 6°C EEC: for the moment, no limit Denmark: max 5°C Sensitivity

Cured meats Heat processed uncured meats

Temperature. The sensitivity to temperature depends on the product composition and on the packaging. Cured meats requiring chilling are usually vacuumpacked or packed in MAP, but the content of salt, and possibly nitrite, gives a certain degree of protection against pathogenic bacteria. Of course a higher storage temperature results in shorter storage life. Heat processed, uncured meat products are sometimes retailpacked in MAP or in vacuum-packs. However, it involves a significant risk of food poisoning if product temperatures are not maintained at the rec-

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Temperature

Odour

★★

★

★★★★

★

ommended or prescribed level, normally a maximum temperature of 5°C. For retail packed meat products, some countries prescribe lower maximum temperatures than 5°C, e.g. 3°C, while other countries allow 8°C. Calculation of loss of quality or remaining storage life can be carried out according to section 2.5 above. However, for several chilled meat products such calculations do not give very precise results, as warm storage in the beginning of the chill chain reduces quality and remaining storage life significantly more than would be found in such calculations.

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5.3 MANUFACTURING MEAT Description This is meat intended for further manufacturing processes. It may be carcases, sides, quarters, primal cuts, and even meat in smaller pieces. However, when the latter group is transported over long distances it is usually in the deep frozen form, see section 3.1 above. Chilled carcases, sides and quarters are often transported without wrapping, usually hung by metal hooks on overhead rails. Cured meat products such as Wiltshire bacon, hams in large packs (6 lbs. or more) are often transported over long distances to be cut or sliced and retail packed at the receiver. Regulations,Standards In the EEC, the Fresh meat directive, the Minced meat directive are the most relevant.

These directives are summarized in section 6.2 in chapter 1. Minimum requirements Raw materials The meat must be of good and sound quality, and at the required degree of freshness. The chilling process must be started as quickly as practicable. In the EEC, the meat should at all points be 7°C or below, before being taken out of the slaughterhouse. Packaging. As mentioned above, transport of unwrapped chilled meat still takes place. This demands special requirements for the loading procedure, but also closer attention to RH (relative humidity) than for wrapped foodstuffs in order to keep the weight loss at the desired level and at the same time to be sure that bacterial

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growth is limited. The recommended RH is 85 to 92%. Beef, principal cuts and similar large pieces are often vacuumpacked in large plastic bags and then placed in corrugated fibreboard cartons. Hence it is called boxed beef. Pork is often packed the same way, but MAP is also used. The large plastic bags must have low gas permeability. The gas mixture could be 50% nitrogen and 50% carbon dioxide, or 100% carbon dioxide. As mentioned before, the colour of beef changes to purple in packagings without oxygen (e.g. vacu-

um-packs), but the bright red colour will re-appear about 15 minutes after opening the package and exposing the beef to the atmosphere. Practical storage life The diagram below indicates the storage life of some types of manufacturing meat. PSL for cured meat products is not included in the diagram, as PSL can be several months at 5°C, especially if the cured meat is heat processed (pasteurized) after being packed in an appropriate packaging.

PSL, weeks

15

10

Beef carcases, unwrapped

5

Beef, primal cut, vac. packed

Pork carcases, unwrapped

Pork primal cut vac. packed °C

-5

0

5

PSL-diagram for some types of manufacturing meat

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Temperature limits Ideal temperature: -1.5°C Legal requirements for transport: ATP: max 7°C EEC: max 7°C Sensitivity Temperature

Odour

Manufact. meat,unwrapped

★★

★★★

Manufact. meat,vac.pack

★★

★

Temperature. For unwrapped meat, temperatures exceeding the prescribed level will reduce the quality and the PSL, but the spoilage bacteria will result in changes so pronounced that there is little risk of the meat being eaten and causing food poisoning. For meat packed in vacuum-packs or MAP, the growth of pathogenic bacteria are of much more concern, because most spoilage bacteria do not grow very well without oxygen in the package. The normal signs of spoilage (off-odour, discoloration) could be lacking, although the product could have experienced such a time-temperature history that there is a real hazard of food poisoning. For cured meat products the sensitivity to temperature depends on the PPP-factors. However, the content of salt. and possibly nitrite, gives a certain protection against

pathogenic bacteria. The temperature should be kept at 5°C or below. Calculation of loss of quality or remaining storage life can be carried out according to section 2.5 above. However, for several chilled foodstuffs such calculations do not give very precise results, as warm storage in the beginning of the chill chain reduces quality and remaining storage life significantly more than would be found in such calculations. Odour Fresh meat, and especially unwrapped fresh meat, is highly susceptible to the uptake of foreign odours from the surroundings, see section 1.7 in chapter 2. The plastic materials used for vacuumpacks and MAP have low permeability, and this reduces (but does not prevent) the uptake of foreign odours.

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5.4 CHILLED POULTRY Description As mentioned in section 3.2 above, poultry is eaten in all parts of the world, and is generally regarded as a highly acceptable foodstuff. Although poultry has a limited PSL at normal chill temperatures (2-5°C) several countries have recently demonstrated a trend towards chilled (fresh) instead of deep frozen poultry. Regulations,standards. The EEC directive 71/118 with further amendments specifies how slaughtering, chilling, cutting, packaging etc. of fresh poultry meat must be carried out. In the EEC countries, the Labelling directive also applies. These directives are summarized in section 6.2 in chapter 1. Minimum requirements. Raw materials The raw materials must be of a good and

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sound quality, and the content of food poisoning bacteria must be as low as is possible. The initial microbial state, i.e. the number and type of microorganisms present on the poultry immediately after chilling and packaging has a pronounced influence on quality and storage life. The processes involved in slaughtering and chilling should be carried out according to good manufacturing practice, and in the EEC countries or for export to the EEC countries according to current EEC directives, e.g. directive 71/118 mentioned above. Other processes are not relevant for “fresh” poultry. Packaging. Fresh poultry meat, e.g. chickens, are normally packed in foodtainers, i.e. a tray overwrapped with a plastic material which has traditionally has been PVC. As can be seen in the PSL-diagram, chicken

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packed this way has a rather short storage life. Vacuum packaging of whole poultry results in only a minor increase in storage life. The use of MAP can increase the storage life considerably, particularly if product temperatures are kept at 2-3°C or below, as is required in some countries. A gas mixture of about 40% carbon dioxide and 60% nitrogen would be used; oxygen is absent as myoglobin is not important for the colour of chickens as it is in the case of beef, see section 5.1 above. Cut-up poultry (chicken portions) are usually packed the same way as whole poul-

try. The storage life of these foods is similar to, or a little less than that for whole birds. An effective method of increasing PSL is to use super chilling (also called deep chilling or partial freezing) where the chickens are chilled to and transported at -2°C (28°F). When the poultry arrives at the wholesaler or at the retailer, the poultry is placed at usual chill temperatures in storage rooms or display cabinets. The PSL-diagram shows that PSL is about 4 weeks at -2°C, and the use of super chilling enables long distance transport of chilled poultry.

PSL, days

30

25

20

15 Chicken, MAP 10

5 Chicken conv. °C -5

0

5

10

PSL-diagram for chilled whole chicken,either conventional packed or in MAP

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Temperature limits Ideal temperature: -1.5°C Legal requirements for transport: ATP: max 4°C EEC: max 4°C Sensitivity Temperature

Odour

Whole poultry

★★★★

★★

Cut-up poultry

★★★★

★★

Temperature. The PSL-diagram above clearly indicates the enormous influence of storage temperature on PSL, and the advantage in using superchilling as is often done in the USA. In order to reduce the growth of spoilage and food poisoning bacteria it is absolutely essential to maintain low temperatures in the chill chain. Temperature abuses during transport will result in a significant reduction in quality and the remaining storage life. The influ-

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ence will be much more pronounced than could be calculated according to section 2.5 above. Warm temperatures in the initial stages of the chill chain promote growth of spoilage organisms, eventually leading to fast spoilage. Odour Fresh poultry easily picks up odour from foodstuffs that give off strong odours, such as oranges, apples, onions, and fish.

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5.5 CHILLED FISH Description. As mentioned in section 2.2 above, chilled (fresh) fish comprise a large number of species with different characteristics. Chilled fish can be whole and gutted fish, fillets or mince. However, chilled fish mince has a very short PSL, and should always be transported in the frozen state. Regulations,standards In the EEC Council Regulation 103/76 with later amendments, common marketing standards for certain fresh or chilled fish are laid down with rules for freshness and size categories. In the EEC, the Labelling directive applies, see section 6.2 in chapter 1. Codex Alimentarius recommended code of practice for fresh fish (CAC/RCP 91976) states that fresh fish should always be carried in melting ice. In order to allow the ice to melt, the temperature in the

storage room must be a few degrees above 0°C. Codex Alimentarius has also issued Recommended Codes of Practice for: Shrimps or Prawns (CAC/RCP 17-1978), Lobsters (CAC/RCP 24-1979), Minced fish prepared by mechanical separation (CAC/RCP 27-1983), and Crabs (CAC/RCP 28-1985), as well as a Recommended Code of Hygienic Practice for Molluscan shellfish (CAC/RCP 19-1978). Minimum requirements. Raw materials The fish must be of good and sound quality prior to the chilling process. The chilling process should be started as quickly as possible in order to minimize growth of microorganisms. Further information on fish is given in section 2.2 above. The best way of maintaining fresh fish at a

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temperature close to 0°C is to keep it in melting ice in a room with a temperature of 1-3°C. If the thermostat in the room is set at 0°C, the air temperature may occasionally fall below 0°C which will prevent the ice from melting. This will inhibit cooling of the fish and cause some parts to freeze. Superchilling (also called deep chilling or partial freezing) to around -2°C may give a longer storage life, but this method is seldom used. Processing Processing, e.g. filletting, should be hy-

gienic and follow the Codex documents mentioned above, see also the Codex documents referred to in section 3.3 above. Packaging. Fresh fish is often marketed unpacked, with ice in the retail tray. Vacuum-packaging or VSP of fish in plastic pouches is a good form of retail packaging. For fatty fish the oxygen permeability should be low as this will increase PSL due to lower oxidation of the lipids. Trout stored at 0°C (in ice) packaged in PE (high oxygen permeability) could

PSL, days

12

10

8

6

Cod fillets

4

2

°C -5

0

5

PSL-diagram for chilled cod fillets at different storage temperatures

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develop a markedly rancid taste after 8 days. For trout vacuum-packed in a plastic material with low oxygen permeability the PSL at 0°C is about 20 days. Vacuum-packaging of lean fish gives a slightly longer PSL, but as mentioned in section 2.2 above, the advantage comes

when the fish is only of secondary quality. MAP is used in some countries, with 30% oxygen, 40% carbon dioxide and 30% nitrogen for lean fish, and 60% carbon dioxide and 40% nitrogen for fatty fish. However, MAP makes cooling of the fish more difficult than with vacuum-packaging.

Temperature limits Ideal temperature: in melting ice (0°C to -0.5°C) Legal requirements for transport: ATP: In melting ice, i.e. 0°C EEC: the temperature of melting ice, i.e. 0°C. Sensitivity Temperature Whole gutted plaice Cod fillets Mince

Temperature. Storage without melting ice (or storage at temperatures above 0°C) will increase the activity of bacteria and lead to rapid spoilage. Bacteria able to cause food poisoning may develop in fish which are not well iced. Clostridium botulinum type E which is often found in fresh fish, can produce toxins at temperatures down to 3.3°C, see table 3.1. Clostridium botulinum can only grow under anaerobic conditions, i.e. where the oxygen concentration is very low. Therefore, vacuumpackaging of fish products in plastic materials with low oxygen permeability and

★★★ ★★★★ ★★★★★

the use of MAP with no oxygen, necessitates product temperatures below 3.3°C. The toxin from Clostridium botulinum type E and harmful bacteria such as Vibrio will be destroyed under normal cooking. However, with fish products intended to be eaten raw such as sushi or oysters, or to be used as raw materials for the manufacture of lightly preserved fish products, such as gravad fish and cold smoked fish (see section 5.6 below), it is very important that the fish is constantly well iced. Heat stable histamine may be formed, in fish of the tuna and mackerel type if they are not stored at low temperatures.

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LIGHTLY AND SEMI-PRESERVED FISH PRODUCTS

5.6 LIGHTLY AND SEMI-PRESERVED FISH PRODUCTS Description This group contains a wide variety of fish products with regional variations. The fish has been treated by one or more of the following treatments: salting, smoking, marinating, heating or addition of preservatives. Such fish products have a longer PSL than fresh fish. Lightly preserved fish products are cold smoked lightly salted salmon, gravad halibut and shrimps in brine. Semi-preserved products are herring fillets in a marinade with a pH lower than 5, and salted cod. Regulations,standards. The only international standard for the transport of preserved fish products is the Codex Recommended international code of practice for smoked fish (CAC/RCP 251979). This recommends that smoked fish which is not treated in such a way as to prevent the outgrowth of Clostridium botulinum type E, should be kept at a tem-

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perature below 3.3°C. Codex Alimentarius has also issued a Recommended Practice for Salted fish (CAC/RCP 26-1979). In some countries, vacuum-packed fish products must be kept below 3°C, and some countries do not allow chilled vacuum-packed smoked fish, simply because of the risk of Clostridium botulinum type E (in these countries such products must be marketed in the frozen state). In the EEC countries, the Labelling directive applies, see section 6.2 in chapter 1. Minimum requirements. Raw materials. The raw materials must be of good and sound quality and be of the required degree of freshness. The processing must be in accordance with good manufacturing practice, and should result in the desired characteristics, e.g. salt/water ratio, temperature, concentration of preservatives, pH, etc.

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Practical storage life The spoilage pattern differs from that of fresh fish, and depends on the method of preservation, packaging, moisture content and temperature. The spoilage is mainly of microbiological origin, but may be oxidation in fatty fish. Smoked fish can

lose the desired distinctive flavour. The examples given below should only be regarded as very rough guidelines because the spoilage -and the storage lifedepends so much on the initial quality and the preserving treatment.

Vacuum-packed sliced gravad halibut at 5°C:

10 days

Vacuum-packed sliced cold smoked salmon at 5°C: (4-5% salt in the water phase)

3 weeks

Shrimps in marinade at 5°C: (pH 5.8 ,benzoic acid added)

5 weeks

Marinated herring fillets at 10°C:

6-10 months

Temperature limits Ideal temperature: lightly preserved products 1°C semi-preserved products 1-5°C Legal requirements for transport ATP: for the moment, no limit EEC: for the moment, no limit Denmark: Lightly preserved fish products, max 5°C In the ATP-Agreement, Annex 3 will probably be revised to state that the maximum temperature for chilled foodstuffs during transport is the temperature indicated on

the label, but must not exceed 6°C. The maximum temperature during transport will be 3°C for chilled vacuum-packed lightly preserved fish products.

Sensitivity Temperature Lightly preserved

★★★★

Semi-preserved

★

Temperature. Most of the products in this group are consumed without further heat treatment. In lightly preserved fish products, there is the possibility of bacterial growth such as Salmonella, Listeria, Vibrio and Clostridi-

um botulinum type E and it is absolutely essential to keep these products at low temperatures and always below 5°C. In semi-preserved fish products there is no such risk, but high storage temperatures will reduce quality and storage life

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LIVE FISH

5.7 LIVE FISH Description This group includes live fish transported in containers with water and live flatfish, eel, crustaceans and molluscs transported in wooden boxes and the like. Regulations, standards Because of the risk of spreading diseases there are veterinary rules prohibiting import of fish from areas with certain diseases. For example the import of live salmonids (i.e. salmon and trout) to United Kingdom is prohibited. This is to protect the salmonids in United Kingdom from the diseases Viral Haemorrhagic Septicaemia (VHS) and Infectious Haematopoietic Necrosis (IHN).

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Minimum requirements. The live fish must be healthy and sound. The recommended temperature is 310°C. Live crustaceans and molluscs should not be kept at temperatures below 4°C, and during the winter live trout should not be suddenly transferred to water several degrees above the temperature of the water they came from. If the temperature of the water in which the fish live rises the fish may suffer as the oxygen level falls below a critical. Oxygen is usually added to the water for transport of live trout and other fish.

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5.8 CHILLED DAIRY PRODUCTS Description Dairy products, especially pasteurized “fresh” milk, are generally regarded as highly nutritious foods, particularly important for children. Dairy products include a complex range of food products, in many cases of an apparently diverse nature, all produced from raw milk: Pasteurized milk, cream, fermented (cultured) milk products, butter, cheese, milk based desserts, etc. Milk in Europe is synonymous with cow milk, but sheep, goat and water buffalo are important to the health and economy of other countries, especially for cheese production. The products dealt with in this section are those dairy products that demand chilling in order to achieve an appropriate storage life.

Regulations, standards Most countries have very detailed legislation on milk and dairy products, for example on temperatures of milk from the farm, the bacteriological and chemical “quality” of the raw milk, the treatment of the milk, the composition of different products (especially milk and butter), etc. In the EEC the Labelling directive (see section 6.2 in chapter 1) applies. Minimum requirements Raw materials Milk is a very good medium for microbial growth. Many dairy products are highly perishable and demand chilled storage. On receipt from the farm the milk is subject to a variety of checks to ensure that the composition and bacteriological standards are met. The majority of milk is pasteurized, commonly at 72-78°C for 15 seconds. In

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many countries, there are legal requirements for pasteurization and for the subsequent chilling process. Heat treatment brings about a considerable reduction in bacterial flora and should ensure absence of pathogenic bacteria. This alone, however, is of no use if packaging etc. allows re-infection. Pasteurized milk Retail packed pasteurized milk has a short storage life and is seldom transported over long distances. Cream Fresh cream is often pasteurized at 95100°C for 15 seconds. UHT-milk and UHT-cream is of increasing importance; UHT products can be stored at ambient temperatures for some months. Fermented (cultured) milk products. Fermentation (culturing) of milk is a very old form of food preservation. There has been a dramatic increase in the consumption of these products which include several types, of which Yoghurt is the best known: Milk is pasteurized at 90-95°C for 15-30 minutes (in some countries 5-10 minutes) and then cooled to 42-45°C. A starter culture, a solution of lactic acid bacteria, is added, and after 2-4 hours the product is cooled to 5°C. Fruit is often added. Butter The cream for butter-making is pasteurized at above 90°C to inactivate enzymes and to reduce the number of microorganisms which would otherwise cause quality loss. Butter is an emulsion of water and oil (fat). The fat emulsion containing in solution sugar, albumen and salt, where as fats and casein are present in celloidal dispersion. There are several common types of butter: Sweet cream unsalted butter (pH = 6.5-6.6), Sweet cream salted

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butter (pH = 6.5-6.6, 1.2% salt), Cultured unsalted butter (pH = 4.6-5-1), Cultured salted butter (pH = 4.6-5.1, 1% salt). Cultured butter is also called fermented or ripened butter. The storage life depends on the quality of the raw milk, salt content and pH, the size of the water droplets, etc. Butter is subject to becoming rancid due to oxidation, producing tallow oily flavours. Another common fault is undesirable flavours picked up from adjacent goods during storage and/or transport. The packaging for butter usually has a low permeability in order to reduce oxidation and dehydration. Butter is not normally transported over long distances together with other foodstuffs. Cheese Milk is transformed into cheese by a process of partial dehydration and a coagulation of the casein. Cheese contains less water than milk. The amount of water in cheese greatly influences the storage life, and its sensory properties. Many types of cheese are stored for a certain period, known as the ripening period, which may last for weeks or months. During ripening the cheese acquires special organoleptic qualities (appearance, texture, flavour). Microorganisms play an essential role in the development of these characteristics. After ripening (at a temperature between 8°C and 25°C for many types of cheese), the cheese should be kept at a temperature between 0°C and the ripening temperature, depending on how long time it is to be stored. Fresh cheeses Fresh cheeses has a high water content and should be kept at chill temperatures. Processed cheeses Processed cheeses are produced from a blend of hard cheeses together with emulsifying salts which is cooled in the molten

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state and re-solidified. Other ingredients such as ham may be present, and the final product may be smoked before packing. Desserts. Fresh cream desserts consist typically of a flavoured base thickened by various types starch, together with pieces of fruit, topped with a fresh, often whipped cream. The risk of contamination in the production together with the combination of ingredients make such products highly perishable, and also present a food poisoning hazard.

Packaging. A wide range of packaging is used for dairy products: Paperboard cartons, glass bottles, plastic pouches (sometimes with low permeability), aluminium foil laminates, grease proof paper, trays or cups made of different materials (often laminates), etc. Practical storage life (PSL) The examples given below should only be regarded as very rough guidelines because the storage life depends so much on the quality of the raw materials, the processing and the packaging (the PPPfactors, see section 2 above).

Pasteurized milk

5-10 days at 5°C 8-14 days at 1°C

Butter

10-20 weeks at 5°C

Cultured milk products

2 weeks at 5°C 3-4 weeks at 0°C

Fresh cheese

2-4 weeks at 5°C

Cheese, Camembert Cheese, Cheddar Cheese, Emmenthal

6-8 weeks at 2°C Several months at 0°C Several months at 10-12°C

Temperature limits Ideal temperature: 0°C to 2°C Legal requirements for transport: ATP: Butter max 6°C Industrial milk max 6°C Cream, Yoghurt, fresh cheese, etc.max 4°C EEC: for the moment, no limit

In the ATP-Agreement, Annex 3 will probably be revised to state that the maximum temperature for chilled foodstuffs during transport is the temperature indicated on the label, but must not exceed 6°C. How-

ever for certain chilled foods the maximum temperature will still be higher. The maximum temperature during transport for butter will be 10°C (and 4°C for raw milk).

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Sensitivity Temperature

Odour

★★

★★★

Pasteurized (liquid) milk

★★★★

★★★

Fermented milk products

★★★

★★

★★

★

Butter

Cheese

Temperature The temperature sensitivity varies widely, depending on the composition (salt content, pH, etc.), but most milk products are, as mentioned before, highly perishable. In order to market high quality products and to obtain the storage life indicated on the label, it is essential to maintain the required temperatures throughout the chill chain. There are several hundreds different types of cheese. The ripening process is reduced, especially for soft cheeses, but is not stopped at chill temperatures. The carriage temperature may vary with the type of cheese and whether or not it is required to ripen during the journey.

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The storage life of most cheeses is not particularly temperature dependent. However, PSL generally increases with decreasing temperature. Freezing, except in rare cases, is undesirable since it changes the texture and spoils the quality. For most soft processed cheeses and cheese spreads it is essential to maintain chill temperatures.

Odour As mentioned before, see section 1.7 in chapter 2, most dairy products easily pick up odour from their surroundings, for example from foodstuffs such as fish, citrus fruits, onions.

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5.9 MISCELLANEOUS CHILLED PRODUCTS Description Several chilled foods, not belonging to the food groups described earlier in chapter 3, are found in the chill chain, and in long distance transport equipment. This includes bakery and confectionery products, eggs and egg products, prepared meals, ready-to-eat dishes, salads (for example mayonnaise based salads), ready-to-eat raw vegetables etc. Regulations, standards As is the case for deep frozen foods, see section 3.6 above, the relevant legislation depends on the product, and different countries sometimes use different types of regulations for the same product. It is therefore impossible, even for the EEC, to indicate the relevant regulations. However, in the EEC the Labelling directive (see section 6.2 in chapter 1) always applies for retail packed foods.

Minimum requirements Raw materials. The raw materials used must be of good and sound quality. The initial microbial state is important for most chilled foods as PSL is usually limited by microbial growth. Good hygienic practice (GHP) should always be followed. Processing. This group comprises so many different foodstuffs that it is not possible to outline the procedures that should be used in manufacture, but good manufacturing practice should always be followed. Packaging. Many different types of packaging are used and it can only be repeated that the packaging used must give the foodstuffs adequate protection, for example against dehydration and oxidation.

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A description of some foodstuffs belonging to this group follows. Margarine Margarine is now seen as a product in its own right rather than as a butter substitute. A significant factor is public awareness of the role of dietary fats in heart disease. A wide variety of different types of margarine are marketed today, differing in raw materials, proportion of polyunsaturated fats, spreading properties, packaging etc. Margarine is rarely subject to microbial spoilage, but may become rancid due to oxidation. Margarine can pick up taints if improperly stored. Eggs Eggs should be collected frequently and chilled as rapidly as practicable. In some countries, eggs which are sound, clean and without cracks may be washed; after drying they may be treated with a suitable mineral oil to reduce weight loss during storage. The packaging must protect the eggs against shocks, vibrations etc. in the chill chain. During storage the temperature of eggs should be around -2°C. Eggs are normally tempered before they are removed from chill storage. This means that the temperature is raised sufficiently so as to avoid condensation of water on the shell. Prepared meals Chilled prepared meals have a limited storage life, often just a few days at 35°C, making such products unsuitable for long distance transport. Chilled meals may be given heat treatment after sealing the packaging, thus improving storage life considerably. This is used for example in the “sous-vide” technique, whereby it is possible to achieve a storage life of 2-3 weeks at 3°C; but for “sous-vide” products it is essential to maintain temperatures below 3°C. When very good hygienic practices (GHP)

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are followed and MAP (e. g. 50% nitrogene and 50% carbon dioxide) is used, the storage life of prepared meals can be increased to 1-2 weeks at temperatures below 3°C. Prepared salads Prepared salads typically consist of chopped vegetables in either a mayonnaise or oil and vinegar base. The best known is coleslaw (basically cabbage in mayonnaise) which also forms the base for many variants including those containing meat or fish. The market for prepared salads has increased vastly in recent years. Care is needed when formulating salads because interaction between ingredients may create conditions suitable for growth of potentially pathogenic bacteria. The traditional coleslaw types are quite stable, but some types have a very short storage life and are fundamentally unsuitable to large scale retailing. Manufacturers of coleslaw and other salads should ensure that raw materials are obtained from suppliers whose practice preclude the possibility of contamination with Listeria monocytogenes or other pathogenic microorganisms. Prepared raw vegetables Ready-to-eat raw vegetables consist of washed and peeled vegetables which have been diced, sliced, grated or otherwise size-reduced. They are becoming increasingly popular either for use as salad component or as ready-to-cook material for a main course. By preparing vegetables in this way the risks of bacterial infection and spoilage are increased, bacteria generally being unable to penetrate the intact surface of plant tissue. Consequently, packaging or storage conditions that would inhibit bacterial spoilage of prepared raw vegetables

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will increase the storage life and saleability of the product. Thus, packaging in plastic materials with low permeability, vacuum-packaging or MAP increases PSL; as with the other products using these systems it is still necessary to maintain cold product temperatures.

Practical storage life (PSL) The examples given below should only be regarded as a very rough guideline because the storage life -and the spoilagedepends so much on the TTT and PPPfactors, see the examples mentioned above. See also section 2 above

Margarine

3 months at 5°C

Eggs

6 months at 0°C 2 months at 5°C

Prepared meals “sous vide”

3-5 days at 5°C 2-3 weeks at 3°C

Ready-to-eat raw vegetable packed in plastic with high WVTR packed in plastic with low WVTR

3-10 days at 5°C 8-28 days at 5°C

Temperature limits Ideal temperature: 0°C to 3°C -2°C for eggs Legal requirements for transport: ATP: for the moment, no limit EEC: for the moment, no limit In the ATP Agreement, Annex 3 will probably be revised to state that the maximum temperature during transport of chilled foods is the temperature indicated on the label, but must not exceed 6°C. However, for certain chilled foods the maxi-

mum temperature will still be different from 6°C.

For prepared meals (vacuum-packed ready-to-eat products) the maximum temperature during transport will be 3°C.

Sensitivity

Eggs Margarine Prepared meals Prepared raw vegetables

Temperature

Odour

★★★

★★★

★

★★

★★★★

★

★★★

★

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Temperature Some products in this group are highly perishable, e.g. prepared meals which have not been treated so as to prevent the growth of Clostridium botulinum (especially type E). Thus it is essential to maintain vacuumpacked (also “sous vide”) ready-to-eat products at 3.3°C or colder in order to eliminate the risk of food poisining. For all foodstuffs in this group low temperatures (i.e. around 0°C) during storage and transport will increase quality and storage life, and reduce the risk of food poisoning.

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Calculation of loss of quality or remaining storage life can be carried out according to section 2.5 above. However, for several chilled foodstuffs such calculations do not give very precise results, as warm storage in the beginning of the chill chain reduces quality and remaining storage life significantly more than would be found in such calculations. Odour Eggs and egg product easily pick up odour from surroundings, and this is also the matter for margarine and some other foodstuffs in this group.

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LIABILITY FOR CARRIAGE OF GOODS

INSURANCE 1. LIABILITY FOR CARRIAGE OF GOODS Goods are often lost, damaged or delayed during transport. This situation is normally followed by the question of who is liable for the losses and to what extent. Anticipating this problem it is possible to assess the needs for and the type of cargo insurance.

The text below describes the Danish law and practice but the liability and compensation described will apply in principle in most other jurisdictions. The liability of the carrier is based on international conventions with the rules and laws common to most countries.

1.1 Sea Carriage The rules about sea carrier’s liability are contained in the Danish Merchant Shipping Act, and the provisions are based on the Hague/Visby Rules of 1968. As a starting point the carrier is liable for loss, damage or delay to goods in the carrier’s custody unless the carrier is able to prove that this is not due to negligence by the carrier himself or anybody for whom the carrier is responsible. This means that the carrier has to prove the cause of the damage and also that the damage is not due to his negligence. Furthermore the carrier is not liable if he proves that the damage is due to a fire, or

caused by the navigation of the vessel. Consequently, typical maritime damage, such as grounding, collision and fire, will not be covered by the carrier’s liability. However the carrier is liable if the loss or damage is due to the vessel’s unseaworthyness at the beginning of the voyage. If the Hague/Visby Rules, as incorporated in the Danish Merchant Shipping Act, apply, the rules are mandatory and the carrier is not able to refer to conflicting provisions in the Bill of Lading. If the carrier is liable for the loss, damage or delay to the goods, the carrier’s liability towards the person or company having the right to the goods is limited to 2 Special Drawing Rights (SDR) per kilo lost, damaged or delayed goods, or a fixed amount, 667 SDR per lost, damaged or delayed unit if this amount is higher. However, the limitation provisions do not apply if it can be proved that the management of the carrier has caused the damage intentionally, or by showing gross negligence, and with the understanding that it would possibly result in damage. The carrier’s liability is limited by the “Global Limitation Provisions” by which the carrier can limit his liability for all losses resulting from the same incident. This limitation amount is calculated on the basis of the tonnage of the vessel. The carrier’s liability is limited to a 1-year

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limitation period as from the date of discharge or the arrival of the vessel at the port of discharge. If legal proceedings are not instituted within the 1-year period the claim will be time-barred, and can no longer be maintained against the sea carrier. Certain detailed provisions apply to giving notice of loss to the sea carrier.

1.2 Road Transport International carriage of goods by road is regulated by the CMR Act incorporating the CMR Convention of 1965. As a starting point the CMR Act provides for almost strict liability of the road carrier for loss, damage or delay of goods. The road carrier is not liable if he proves that the loss, damage or delay was caused by a wrongful act, or negligence of the claimant, by the instructions of the claimant given otherwise than as a result of a wrongful act or negligence on the part of the carrier, by the inherent nature of the goods, or through circumstances which the carrier could not avoid, and the consequences of which he was unable to prevent. As will be seen the burden of proof lies with the carrier, but if the carrier succeeds in proving that the loss, damage or delay might be attributed to one of several special causes, such as bad stowage performed by the shipper, the burden of proof shifts to the plaintiff who must then prove that the loss, damage or delay was not, in fact, wholly or partly, due to one of these causes. The damages recoverable for total or partial loss of the goods are to be calculated by reference to the value of the goods at the place and time they were accepted for carriage. The liability is limited to a fixed amount, 8,33 SDR per kilo gross weight losts or damaged.

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In the case of delay the damages are limited to the amount of charges for carriage unless a surcharge is paid to cover a higher value declared in the consignment note. A limitation amount does not apply if the carrier has been guilty of wilful misconduct, or if his servants or agents have been guilty of wilful misconduct in the course of their employment. The act provides that the period of limitation for a claim against the carrier shall be 1 year. The period limitation runs in the case of partial loss, damage or delay from the date of delivery, in the case of total loss from 30 to 60 days from the date the carrier took charge of the goods, and in all other cases 3 months from the date the contract was entered into. In case of wilful misconduct the period of limitation is 3 years. The Act contains certain rather unclear provisions about suspension of time and about notice of loss. For national, rather than international, carriage of goods by road either the liability provisions in the Road Traffic Act, or the Danish Common Rules for Compensation will apply.

1.3 Air Carriage The stipulations about the air carrier’s liability towards the cargo are contained in the Act of Air Carriage which is based on the Warsaw Convention of 1929 with later changes and amendments. Since this convention is widely accepted throughout the world, the general rules are common to all countries with only a few details particular to certain nations. The air carrier is liable for loss, damage

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or delay of goods in his custody unless he proves that he took all reasonable measures to avoid the damage, or that it was impossible to take such measures. In practice this is interpreted to mean that the air carrier has to prove the cause of the damage, and prove that the damage was not due to negligence by himself or anybody for whom he is responsible. The air carrier’s liability is also limited. The limit of liability is a fixed amount,presently 17 SDR per kilo lost, damaged or delayed. The air carrier cannot apply this provision if the damages have been caused by wilful misconduct. The claim against the air carrier will be time-barred if legal proceedings are not instituted within 2 years of the date on which the aircraft arrived, or should have arrived. Some further provisions about notice of claim can apply.

1.4 Rail Carriage The railway’s liability towards the cargo are contained in the Danish Railways Act which, to a large extent, is based on the International Convention of Carriage of Goods by Rail, the CIM Convention. Danish railway’s (DSB’s) liability towards the cargo interest is very much like the road carrier’s liability. However, DSB’s liability is limited to 21 US$ per kilo.

2. INSURANCE

2.1 As will be seen, sending goods from one country to another as a part of a commercial transaction can be a risky business. Thus, it is important for the parties in an international contract to decide whether a

cargo insurance is to be taken out and, and if so, whose duty it is to arrange for the insurance. By using the EEC-”Incoterms 1990” which provide a set of rules for the interpretation of the most commonly used trade terms in international trade, the parties also agree who is going to take out the insurance. A number of the Incoterms 1990 deal with the question of taking out insurance such as CIP (Carriage and Insurance Paid to (....named place of destination)), and CIF (Cost, Insurance and Freight (....named port of destination)).

2.2 The most common insurance conditions are the Institute Cargo Clauses (A). These cover all risks of loss or damage to the subject-matter insured except as provided in the exclusion clauses. The insurance covers loss of, or damage to, the subject-matter resulting from any variation in temperature, attributable to breakdown of refrigeration machinery resulting in its stoppage for a period of not less than 24 consecutive hours. With regard to insurance of frozen food the common conditions are the Institute Frozen Food Clauses (A) (excluding frozen meat), and damage due to variations in temperature are only covered if the variation is due to a breakdown of machinery for more than 24 consecutive hours, fire, explosion, a vessel’s grounding, sinking, capsizing or collision, capsizing or derailment of land transport vehicle or discharge in a port of refuge. Also, the Institute Frozen Meat Clauses (A) will cover risks of, or loss of, or damage to, the cargo insured under certain

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conditions with regard to preparation of the cargo for transportation. Finally the Institute Frozen Food Clauses (Full Condition) give a very wide coverage as the insurance covers loss of, detorioration of, or damage to the interest insured from any cause which might arise during the period of the insurance. This insurance is very seldom agreed upon with cargo underwriters.

receiving the consignment, the carrier must contact the party shipping the goods before the shipment proceeds. In the case of road transport the driver should inform his employer of the situation so that instructions can be given while the trailer is still at the supplier’s loading bay.

Since the cargo insurance covers the losses suffered by the cargo interests immediately after the insurance conditions are fulfilled, it is highly recommended that a cargo insurance be taken out instead of awaiting the clarification of the question of the carrier’s liability and consequently only receive a limited amount as compensation.

Furthermore, during the journey the carrier must regularly check the carriage temperature. If the refrigeration unit is provided with an automatic recorder of the air temperature in the transport equipment, this apparatus must be in good working order and the apparatus must be fitted with a recording disc or tape so that the measured temperature can be recorded. The latter is of course important evidence, if damage arises to the consignment as a consequence of temperature variances during the journey.

3. INSTRUCTIONS TO THE CARRIER

Stowage On loading a consignment into the transport vehicle, the following two considerations are of great importance:

Temperature Before the start of transport, the carrier must have received instructions on the carriage temperature, i.e. the temperature at which the consignment must be transported. On loading, the carrier must always (by means of random sampling) check the temperature in the consignment, which has been received for transport. A reasonably correct thermometer, see chapter 1 section 7.3, is a necessary tool. The minimum and maximum temperatures measured must be stated in the transport document. If significant discrepancies are noted between the required transport temperature and the temperatures measured on

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1) Air circulation The goods should always be loaded in such a way that there is the possibility of free air circulation around the goods. 2) Securing the goods Goods must be stowed and secured in such a way that the normal shocks and vibration accociated with transport do not cause the load to shift.

If the transport is to be carried out by using a trailer, it is recommended that the driver be present at the loading of his trailer/lorry, and when necessary, show the staff at the place of loading how he wants the goods placed in the trailer, This is partly to ensure the optimum circulation of the cooling air, partly for the sake of road safety, and of course to prevent

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other kinds of damage to the consignment or the equipment.

doubt as to the connection between the written remarks and any later complaint of damage to the consignment.

4. CONTROL ON DELIVERY

On arrival every consignment must be checked by the consignee before signing any form of receipt on the freight document. If there are remarks to be made regarding the condition of the consignment they should be made on the freight document. The goods should be examined for visible damage and the temperature of the goods measured, preferably the product temperature rather than the temperature of the packaging. In addition, the recorded temperatures - if a suitable temperature recorder is installed - must be examined, as must the temperature setting on the control panel. If the consignment has arrived in a damaged condition, it is important to record the first impression of the condition of the consignment. This is important for subsequent treatment of the damaged cargo and the insurance claim. Taking photographs before and during the unloading of the cargoe is a good way of recording and documenting the visible condition of the consignment. The original temperature recording chart, or a photocopy should be kept as evidence of the temperature conditions during the transport from the supplier to the consignee. It is also important that any reservation regarding the condition of the goods be recorded on the freight documentation. This reservation must not be phrased generally, as for instance “received with reservation”. The reservation must be phrased precisely so that there will be no

5. SECURING THE EVIDENCE IN CASES OF DAMAGED GOODS

If damage arises to the transported consignment, the claimant - usually the importer or buyer - will apply for compensation for his loss from the insurers involved. The insurers will usually be 1) Cargo insurers if seller or buyer has taken out a transport insurance, and if the contract conditions cover the particular case. 2) The carrier’s third party liability insurers.

The two types of insurance are basically the same, except for one essential difference; As a rule the cargo insurers will compensate damage arising from a sudden unexpected event. The third party liability insurers, however, are only liable, if the damage concerned has arisen as a consequence of circumstances for which the carrier is responsible. There is also the possibility of limitations of indemnity, due to the relevent transport regulations governing and restricting the carriers risk. All international insurance companies have a network of “average agents” throughout the world. On behalf of the insurers (the principals) they have committed themselves to the objective treatment of each claim. In an average situation the claimant (im-

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porter/buyer) applies to either the insurers or the local average agent of the insurers. Alternatively, contact is made to the carrier who, via information in his third party liability policy, contacts the average agent. The most important part of the treatment of the case in an average situation is the survey of the damaged consignment. The purpose of this survey is to ascertain the facts, i.e. the nature, extent, and the cause of the damage. If it is found necessary, special expertise is called in (e.g. scientists or engineers) to assist the insurers average agent in the execution of the survey. The insurers average agent must collect all necessary relevant documentation, e.g. commercial invoice, freight bill, special transport instructions, temperature information, etc. After this, a survey report is issued, which should be an objective, detailed description of the damage concerned. As a rule the survey report must contain information and documentation covering:

a) the nature of the damage b) the cause of the damage c) the extent of the damage The survey report is important in the insurers’ subsequent treatment of the transport damage, including, of course, the judgment of the responsibility/liability to pay damages. It goes without saying that a survey report is an important document, particularly if later it should be necessary to go to court or to arbitration in order to settle the degree of liability.

Because of the perishable nature of the cargo it is important that all the parties involved, importer, buyer and carrier, secure all possible evidence while the damaged consignment is still available. Therefore, it is strongly recommended that the parties, together or separately, ensure that survey reports are issued. If an importer/buyer has not taken out a special transport insurance and if there is no insurance information from the seller, the importer/buyer can always seak advice and instruction from his own insurers.

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DEFINITIONS AND EXPLANATIONS

DEFINITIONS AND EXPLANATIONS Definitions and explanations of some terms and expressions used in relation to transport and storage life of the chilled and frozen foodstuffs dealt with in this book are given in this chapter.

ATP. Agreement on Transport of Perishables (ATP) is an international agreement on the transport of perishable foodstuffs, see chapter 1 section 6.1. AW see water activity

CHILL CHAIN The chill chain comprises the different stages from production to cooking or consumption, i.e. chill storage, transport, local distribution and display (for example in a supermarket display cabinet).The consumer's handling of the product , transporting it home and storage in refrigerator is part of the chill chain. In order to maintain product quality and, especially, reduce growth of microorganisms it is vital to maintain the correct temperatures throughout the chill chain.

CHILLED FOODS Foods which have been subjected to a chilling process and afterwards are kept at chill temperatures are considered as chilled foods.

CHILLING. Chilling (chilling preservation) is defined as bringing the product temperature down to chill temperatures,i.e. temperatures ranging from about -1.5°C to +8°C,and maintaining this temperature. In some cases the temperature can be a little higher, e.g. +14°C for bananas, or a little lower, e.g. -2°C, see Superchilling below. CHILLING INJURY Chilling injury is physiological damage caused to fruit and vegetables by exposure to temperatures below a critical threshold for each species, but above freezing temperature. CHILLING PROCESS The chilling process is the process used to reduce product temperatures from the initial temperature to chill temperatures. The most commonly used chilling processes are summarized in section 5.0 in chapter 3. COLD CHAIN This term is sometimes used as synonymous with freezer chain, or to chill chain. Thus, cold chain could mean either or both, see also cooling, below. COLD SHORTENING The term used to describe the irreversible phenomenon that causes considerable toughening to meat, especially beef, veal and lamb. It is caused when a hot car-

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cass has been cooled too rapidly resulting in severe contraction of the muscle. COOLING Cooling means a reduction in the product temperature, or maintaining the food at temperatures below ambient, either chill temperatures or freezer temperatures. CSW Chilled Sea Water is a storage method for fish, involving the total immersion of fish in a liquid (sea water) held in a tank. The sea water is kept at around 0°C by adding ice.

DEEP-FROZEN FOODS The term deep-frozen foods (surgele, tiefgefroren) is correctly used when the product temperature is maintained during storage,transport and retail sale at -18°C or colder with a minimum of fluctuations. The freezing process used must be reasonably rapid.

Deep-frozen foods are often denominated quick-frozen foods.

ENTHALPY Enthalpy is the total heat content of a food product. It is measured in kJ/kg, and is set at 0 kJ/kg at -40°C. EQUILIBRIUM TEMPERATURE Equilibrium temperature or mean temperature is the temperature which is achieved when the surface temperature and the centre temperature become practically identical after an equalization period.

After for example a quick chilling process the surface temperature may be -1°C,the centre temperature +15°C, but the equilibrium temperature could be +4°C.

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FREEZER CHAIN Like the chill cain above the freezer chain comprises all stages from production (right after completion of the freezing process) to cooking or consumption. FREEZING Freezing (freezing preservation) comprises the freezing process, freezer storage and - in most cases - a thawing process. Foods which have been subjected to a freezing process are considered frozen foods. In industrial and commercial practice there are two temperature ranges for storage and retail display, namely frozen foods and deep-frozen foods (or quickfrozen foods). In French: congelé and surgelé, in German: gefroren and tief gefroren (or tiefgekühlt). FREEZING INJURY The damage - mostly texture deterioration - caused by exposure of the foodstuff to temperatures below the (initial) freezing point of the foodstuff. FREEZING POINT The freezing point - or more correctly the initial freezing point - for foods depends on the composition of the food, i.e. the content of water, salt, etc. The initial freezing point of many raw foods is around -1.7°C. When food is cooled to this temperature,ice begins to form. As the food is cooled below its initial freezing point, more and more water is turned into ice so that the residual solution will become more and more concentrated. Even at -40°C some unfrozen water remains. FREEZING PROCESS During the freezing process a high proportion of the water in the food product (many foods contain 70-90% water) is converted into ice.The process should be

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started as quickly as practicable after the food product has undergone the the necessary preparation procedures such as cutting, washing, possibly packaging, etc. The freezing process shall be as rapid as practicable. FREEZING RATE The freezing rate is defined as the speed of movement of the ice front through the foodstuff. See chapter 1 section 3.0 FREEZING TIME Freezing time is defined as the time elapsed from the start of the freezing process until the final temperature is reached. For further information, see chapter 3 section 3.0. FROZEN FOODS Throughout the industry and among consumers, the term frozen food normally means deep (quick) frozen foods. Frozen foods simply is foods that are sold frozen, i.e. at a temperature well below 0°C. From a legislative point of view it is necessary to distinguish between frozen and deep frozen foods. In legislation, the term frozen foods (congele,gefroren) is used for a limited group of products (meat and poultry) which are maintained at a steady temperature of -10°C (or -12°C) or colder, see chapter 3 section 4. (Deep (quick) frozen foods are kept at -18°C or lower).

GMP GMP (Good Manufacturing Practice) may be defined as current good practice in manufacturing, processing and holding food products.

K-COEFFICIENT K-coefficient (or K-value) is a measure of the effectiveness of the insulation in

transport equipment (and in cold storage rooms etc.), see chapter 1 section 6.1.

MIGRATION Migration of additives from a packaging material into foodstuffs, see chapter 1 section 6.3.

POSITIVE LIST Lists of approved additives/components with maximum concentrations, all others being banned. See chapter 1 section 6. PPP The PPP-factors (Product, Process, Packaging) can be as decisive for product quality as storage temperature and time, see chapter 3 section 2. PRACTICAL STORAGE LIFE (PSL) The practical storage life of a food product is the period after chilling/freezing during which the product retains its characteristic properties and remains fully acceptable to the consumer/ processor.

PSL see Practical Storage Life

QUICK-FROZEN FOODS This term is often regarded as synonymous with deep-frozen foods, see above.

RELATIVE HUMIDITY ( RH ) The ratio of the quantity of water vapour present in the air to the quantity that would be present if the air was saturated at the same temperature. It is also defined as the ratio of the pressure of water vapour present to the pressure of saturated water vapour at the same temperature.

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RSW RSW (Refrigerated Sea Water) is a storage method for fish involving the total immersion of fish in sea water held in a tank. The sea water is kept at 0°C to -1°C by means of a mechanical refrigeration system.

SHORT-CIRCUITING When used in relation to refrigerated storage or transprot equipment it refers to the circulating air that by-passes the majority of the cargo by flowing through gaps inadvertently left in the stow, resulting in poor air distribution.

-2°C, in some cases as low as -3°C or -4°C, is used.

TEMPERING Tempering means heating a frozen foodstuff from its initial temperature to the thawing plateau, i.e. tempering is the first part of a normal thawing process, see chapter 3 section 3.0. TTT TTT (Time-Temperature Tolerance) is a product’s storage life at different storage temperatures, see chapter 3 section 2.

SHORT-CYCLING The term given to a defective part of a control system that switches a machine on and off too frequently.

VSP VSP (Vacuum Skin Packaging) is a special form of vacuum-packaging, see chapter 1 section 4.1.3.

SPECIFIC HEAT. The amount of heat (expressed in kJ) required to raise the temperature of 1 kg of a substance 1°C. The specific heat of chilled foods is about 3 kJ, depending on the composition, mainly the water content. The specific heat of deep frozen foods is about 1.5 kJ, depending on the water/ice content. See chapter 3 section 3.0.

WATER ACTIVITY The ratio of the water vapour pressure of the solution (the foodstuff) to the water vapour of pure water at the same temperature.

SUPERCHILLING Superchilling, often called deep chilling, means chilling the food to a temperature a little below the initial freezing point, and maintaining this temperature during storage and transport. A temperature about

UHT UHT (Ultra High Temperature) is a process where milk (or similar foodstuffs) is heated to at least 132°C for at least 1 second. The heated product is then aseptically packed in plastic coated paperboard cartons. UHT products can usually be kept at room temperature for several months, and do not require refrigerated transport.

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INDEX

INDEX * after a word/term indicates that the word/term ix explained or defined in chapter 5 (page 151-154).

Air circulation .....................45, 63, 66, 72 Air temperature measurement.............37 Aluminium foil ......................................18 ATP*...............................................25, 88 Average agent ...................................147 Average temperature, see equilibrium temperature ......89, 114 aw, see water activity* .................80, 154 Barrier layer .........................................18 Beef, see meat BGA (Bundes Gesundheits Amt).........33 Board, see paperboard........................22 Bottom air delivery.........................52, 54 Bracing ..........................................64, 73 Butter, frozen .....................................111 Butter, chilled .....................................133 Calculation of quality loss ....................86 Calibration of thermometers ................40 Capacity control...................................51 Carbon dioxide cooling ........................69 Cartons....................................18, 21, 24 CA-storage ..........................................12 CAPTECH ...................................20, 116 Cheese ..............................................134 Chicken, see poultry Chill chain*.........................................151 Chilled foods* ..............................87, 114 Chilled foods, see under the specific product Chilling* .............................................151 Chilling injury*......................................11 Chilling process*................................114

Code of good transporting practice .....72 Codex Alimentarius .....................35, 127 Codex standards ...........35, 99, 102, 105 Cold chain* ........................................151 Cold shortening*..........................93, 114 Coleslaw ............................................138 Colour changes ...................................82 Compressor ...................................50, 52 Condenser ...........................................50 Condensation ................................14, 50 Concentrated fruit juice......................102 Consumer packs..................................16 Containers ...........................................54 Containers,air circulation .....................57 Controlled atmosphere*.......................12 Controllers .....................................58, 64 Cooling* ...............................................15 Cooling during transport ......................75 Corrugated board ..........................22, 47 Cream................................................134 Cryogenic refrigeration ........................69 CSW*.................................................114 Cured meat................................118, 121 Dairy products ...................................133 Deep chilling, see superchilling*........125 Deep-frozen foods*, see under the specific product Defrosting ............................................53 Dehydration .........................................14 Delivery air control...............................58 Delivery vans .......................................70 Desiccation ..........................................14 Directives, EEC....................................27 EEC-directives ...............................27, 88 Eggs ..........................................108, 138 Enthalpy* .............................................92 Equilibrium temperature* .......24, 89, 114

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Eutectic plates .....................................69 Evaporation....................................14, 51 Evaporator .....................................50, 52 FDA (Food and Drug Administration) ..32 Fish, raw material ................................84 Fish, chilled........................................127 Fish, deep frozen.................................99 Fish, live ............................................132 Fish products, chilled.........................130 Flavour changes ..................................82 Flushing ...............................................20 Flutes...................................................23 Foodtainer ...........................................19 Food poisoning ....................................81 Freezer burn ........................................15 Freezing* .............................................88 Freezing injury*....................................11 Freezing methods ................................90 Freezing point*.........................11, 45, 88 Freezing process*................................88 Freezing rate* ......................................85 Freezing time*......................................89 Frost formation...............................14, 53 Frozen foods*.....................................111 Fruit, deep frozen...............................102 Fruit, concentrate...............................102 Gas flushing.........................................20 Genset .................................................56 Glazing ........................................99, 101 GMP* ...................................................84 Heat sources .......................................44 Heaters (electric) .................................53 Hot-gas bypass..............................51, 53 Inner packaging ...................................16 Inside frost formation ...........................14 Insulated containers ......................70, 71 Insulation .............................................44 Insurance...........................................143 Integral containers ...............................55 Irradiation.............................................34 ISO ......................................................27 ISO-containers...............................43, 54 K-coefficient* .................................26, 44

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K-value, see K-coefficient ....................44 Labelling directive, EEC.......................28 Lamb, see meat Laminates ............................................18 Legislation ...........................................25 Loading..........................................46, 73 Load line ........................................47, 55 Loss of quality......................................86 Machinability........................................17 MAP.............................20, 116, 119, 129 Margarine ..........................................138 Masterpack ..........................................20 Meat, raw material ...............................84 Meat, chilled ......................115, 118, 121 Meat, deep frozen................................93 Meat, frozen.......................................111 Meat products, chilled........................118 Mechanical refrigeration ......................50 Microbiological standards ..............30, 31 Metal cans ...........................................18 Microbiology ........................................79 Microorganisms ...................................79 Migration* ......................................32, 33 Milk ....................................................133 Mixed loads .........................................49 Mobile freezers ....................................90 Nitrogen cooling...................................69 Odour.............................................49, 88 Outer packaging ..................................21 PA, Polyamide, Nylon...........................17 Packaging ......................................16, 86 Packaging forms ..................................18 Packaging materials ............................16 Pallet....................................................48 Pallet patterns......................................48 Paperboard ..........................................22 Pathogenic microorganisms ................81 PE, Polyethylene..................................17 Permeability .........................................16 PET, Polyester .....................................17 Plastic bags, pouches..........................19 Polyamide (PA) ....................................17

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INDEX

Polyethylene (PE) ................................17 Polyester (PET) ...................................17 Pork, see meat Porthole container .........................54, 55 Positive list* ...................................32, 33 Poultry, chilled....................................124 Poultry meat directive ..........................29 Poultry, frozen ....................................111 Poultry, deep frozen .............................96 PPP* ..............................................83, 87 Practical storage life(PSL)*............83, 87 Pre-cooling ..........................................46 Pre-cooling transport equipment .........46 Primary distribution vehicles................62 Primary packs......................................16 Product groups ..............................79, 87 PSL, see Practical Storage Life .....83, 87 PTI .................................................59, 72 PVC .....................................................18 Quality changes...................................79 Quality loss ..........................................86 Quick-frozen foods* .............................88 Quick-frozen food directive ..................27 Ready-to-cook dishes........................137 Ready-to-eat dishes ..........................137 Refrigeration capacity....................51, 63 Refrigeration, principle.........................50 Refrigeration cycle...............................50 Refrigeration process ..........................50 Refrigeration systems....................26, 69 Refrigeration unit ...........................51, 56 Regulations....................................25, 87 Relative humidity (RH)* .......................12 Remaining PSL....................................86 Retail packs .........................................16 Return air control ...........................58, 64 RH, see Relative humidity ...................12 RSW*.................................................114 Rule of additivity ..................................86 Salmon, see fish Secondary distribution vehicles ...........70 Secondary packaging ....................16, 21 Sensitivity ............................................88 Set-point ........................................58, 64

Shipping containers .......................16, 21 Short-circuiting* .............................47, 64 Short-cycling* ................................58, 65 Slip sheet.......................................48, 49 Specific heat*.......................................92 Storage life, see PSL ...........................83 Stowage pattern ..................................46 Superchilling*.....................118, 125, 128 Survey report .....................................148 T-bar ..............................................52, 57 Temperature control system ..........58, 64 Temperature fluctuations .....................15 Temperature limits ...............................88 Temperature monitoring.......................36 Temperature measurements................36 Temperature recording ............39, 60, 67 Temperature recorders ..................60, 67 Tempering* ..........................................92 Texture changes ..................................82 Thermoforming ....................................21 Thermometers .....................................39 Thermostats ........................................53 Thin wall vehicles.................................71 Top-air delivery ....................................63 Trailers ...........................................43, 62 Transport cartons...........................16, 21 Transport equipment......................25, 43 Transport packaging ......................16, 21 Trunkers...............................................62 TTT*.....................................................83 Turkey, see poultry Vacuumpackaging ...............................19 Vegetables, deep frozen ....................105 VSP* ............................................20, 128 Water activity (aw)*..............................80 Water loss............................................14 Wrappers .............................................19 WVTR ..................................................16 UHT*..................................................134 UIC ......................................................27 Unit loads.............................................47 Unloading ......................................46, 74

157