Egg Quality Guide

Egg Quality Guide

Contents Introduction

3

Section 1 1

The Structure of the Egg

4

2

Egg Formation

6

3

Common Internal and Egg Shell Faults

9

4

Composition and Nutrient Content of Eggs

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5

Effects of Storage Upon Egg Quality

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Section 2 1

Grading of Eggs For Human Consumption

2

Quality Standards – The EU Egg Marketing

3

17

Regulations and Other Controls

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Quality Control Methods for Eggs

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Section 3 Glossary of Terms

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Section 4 Pictorial Guide to Egg Quality

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28

Introduction

Introduction The egg was never intended to be eaten, yet it has been used in human diets since early times. There is evidence that wild birds eggs were included in the diets of primitive peoples long before the development of agriculture. Today, eggs remain a staple food within the human diet, consumed by people throughout the world. They are recognised by consumers as versatile and wholesome and they have a natural balance of essential nutrients. However, eggs have to compete for sales with an increasing number of other products in the modern food industry and to compete successfully they have to overcome certain disadvantages. For example, they are fragile and they deteriorate in quality with age. Furthermore, each of the main components of the egg (the shell, the albumen and the yolk) has a natural variability which is not in keeping with the modern consumers requirement for consistency. Planned production methods and efficient quality control procedures help to reduce this variation and are fundamental to the successful marketing of eggs. All those involved in production, grading and packing must be aware of the defects which can occur in eggs, the likely causes and the means of identifying and removing those which are unsuitable. It is hoped that this book will be of relevance and interest to all those involved in the production and marketing of eggs for human consumption. In Section 1, information is presented on the structure, formation and nutrient content of the egg and on the causes of common quality faults. Section 2 summarises current legislation and provides a guide to quality control methods for those involved in pre-candling and candling inspection of eggs. Definitions of some of the technical terms used are given in Section 3 whilst Section 4 contains a pictorial guide to egg quality.

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1 T he st r u c tur e o f th e e gg An egg consists of a yolk at the centre, surrounded by albumen (white), both of which are enclosed within the shell. However, the detailed structure of an egg is more complex than it first appears as the diagram at Figure 1 shows.

The Yolk The yolk consists of fats, vitamins and minerals, together with about half of the egg’s total protein content. A transparent barrier called the vitalline membrane surrounds the yolk and prevents the yolk contents leaking into the albumen. Inside the yolk is the germ cell (or germinal disc). This is the site of cell division if the egg is fertile. The colour of the yolk varies and it is influenced by the laying hen’s diet. The colour of the yolk has no connection with food value.

Fig 1 The structure of an egg

The Albumen Egg albumen is rich in protein and vitamins and it contains substances which protect the egg from micro-organisms which may have entered through the shell. In a freshly laid, good quality egg, alternating layers of thick and thin albumen are clearly visible. The innermost layer of thick albumen (the chalaziferous layer) is extended at two points, forming the white, fibrous chalazae

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Section 0ne

which are anchored in the outer thick albumen. The structure of the albumen is designed to provide support and protection to the yolk, holding it centrally inside the egg.

The Egg Shell The egg shell consists of the inner and outer shell membranes, the true shell and the cuticle. In total it is approximately one third of a millimetre thick and over 90% of it is made of calcium carbonate. There are also small quantities of proteins and other minerals. Several thousand tiny pores permeate the shell, the majority of them are usually at the broad end of the egg. The pores allow gases to move between the contents of the egg and the surroundings. The diagram in Figure 2 shows a transverse section through an egg shell.

Fig 2 Transverse section through an egg shell

The two shell membranes have a dense structure which inhibits the movement of micro-organisms into the egg. They also act as a foundation, providing a solid base upon which the true shell is built. The true shell is built in columns of calcium carbonate from individual ‘seeding sites’ on the membranes. When completed, the shell is rigid but brittle. Shell strength is determined not only by shell thickness but also by shape and structure. The outermost part of the shell is the cuticle which gives the egg its characteristic bloom or shine. When the egg is laid, the cuticle is still moist although it will dry within a minute or two. The cuticle normally covers the pores and this provides extra microbiological protection, especially when the egg is fresh.

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2 Eg g f or m a ti o n The formation of an egg can be compared to an assembly line in a factory. A number of component parts are needed and these must be assembled in the correct order and quantity. If the process is disturbed or becomes de-synchronised, faults will occur. Egg formation and development occurs in the ovary (where the yolk develops) and the tube-like oviduct which acts as the assembly line. Most female animals have two active ovaries and oviducts but in the hen, only the left ovary and oviduct is functional. The right ovary and oviduct remain dormant. Figure 3 shows a representation of a mature ovary and oviduct from a laying hen.

Fig 3 The hen’s reproductive system

Yolk Development In the ovary, the yolk develops from a minute ovum. A female chick is born with a miniature version of the fully formed ovary but this hardly changes in size during the growing stage. When the hen reaches maturity, the ovary begins to increase in size. Each ovum (the future yolk) begins to develop during an active growth stage, a process which takes 7-10 days in all. The developing yolks are enclosed in a sac or follicle. They are spherical in shape and each one is attached by a stem to the

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Section One

ovary wall, so that the whole structure looks like a bunch of grapes. The sacs have an excellent blood supply which delivers essential nutrients. As each yolk grows, its colour changes from pale grey to a characteristic yellow.

Ovulation and Egg Laying When the yolk reaches its final size, it breaks away from the ovary. This process is called ovulation. The yolk enters the oviduct (see opposite) where the albumen and the shell are added. The process from ovulation to egg laying takes around 24-26 hours. Shortly after an egg is laid, ovulation takes place again. Another yolk is released into the oviduct and the process which will lead to the next day’s egg begins again. The interval between the laying of one egg and the ovulation of the next is approximately 30 minutes. The timing of egg laying gets gradually later each day. Hens in full production will lay an egg each day for several days and this group of eggs is known as a clutch. Each clutch is followed by a sequence of one or more days when the bird does not produce an egg.

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The parts of the oviduct The oviduct is like a coiled tube which, if straightened, would be 60-80 cm in length. It extends from the ovary to the cloaca and varies in diameter along its length. It can be divided into five distinct parts.

1 The Infundibulum (Funnel) The infundibulum is the entrance to the oviduct, where the yolk is captured after ovulation. It begins in a funnel shape, some 9cm in diameter but narrows quickly. In a hatching egg, it is the site where fertilisation takes place. The yolk takes around 15 minutes to pass through this area.

2 The Magnum The magnum is the longest section of the oviduct and the egg takes some 3 hours to pass through. It is here that the albumen is added. The egg rotates, so producing and stretching the chalazae. The albumen is laid down in circles around the yolk.

3 The Isthmus The addition of albumen is completed and the shell membranes are formed in the isthmus, a process taking around 1-11⁄4 hours.

4 The Shell Gland The shell gland area consists of the tubular shell gland and the shell gland pouch. As the egg moves through, a watery secretion is added to the albumen. Gradually, this plumps up the egg until the shell membranes become stretched. This provides a firm base on which the true shell can form. The shell formation process takes just over 20 hours and finishes with the addition of pigment and cuticle which give the shell its colour and bloom.

5 The Cloaca The egg is released through the cloaca or vent. The muscles in the uterus contract and invert. The egg is pushed out, usually broad end first.

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Section One

3 C o m mo n i n te rn a l & eggshell faults Many different factors can disturb the egg formation process and these in turn can increase the incidence of second quality eggs. Eggs can also be damaged after they are laid, either by cracking or by contamination. Some typical internal and external faults and abnormalities are listed below together with their likely causes.

Internal Egg Quality Faults & Abnormalities Double Yolked Eggs In a young, highly productive laying hen, two yolk ovulations may take place almost at the same time. When this happens, the two yolks progress as one down the oviduct in juxtaposition and they enter the shell gland together.

Blood Spots in Eggs These are normally found in or around the yolk. They can be caused by one of the tiny blood vessels in the ovary breaking at the time when the yolk is released. High levels of activity or disturbance, particularly at the time of ovulation are likely to increase the incidence of these. Eggs from free range laying hens may have some protection from blood spots due to rutin, a substance in the grass which has some effect in stopping bleeding.

Meat Spots in Eggs Meat spots are usually brown in colour and associated with the albumen rather than the yolk. They often consist of small pieces of body tissue, such as the internal wall of the oviduct. Their incidence varies according to bird age and health and also due to strain (breed) differences. In brown shelled eggs, they are more difficult to identify without breaking the shell and there is also evidence that brown laying hens are more likely to produce them than white hens.

Watery Whites The internal quality of freshly laid eggs deteriorates with increasing flock age and some eggs from older birds may have unacceptably watery whites even when laid. Viral diseases such

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Double yolked egg

as infectious bronchitis can also affect the ability of the bird to produce thick albumen.

Abnormal Yolk Colour The colour of the yolk is determined by the diet of the bird, although some disease conditions can also contribute. Green yolks can be caused by birds consuming green herbage to excess. The colour can vary from olive to khaki but may only affect a proportion of birds within a flock. The fault occurs most frequently in the spring when herbage is most lush and where birds take a higher proportion of their feed from the range.

Mobile & Bubbly Airspaces Although the airspace usually forms at the broad end of the egg, it can occasionally be found where there is a shell structure fault or abnormality. In other casaes, a bubbly air space may be seen within the albumen and this is usually caused by a ruptured inner membrane.

Bacterial and Fungal Contamination Mobile airspace

Bacteria and moulds may naturally be present on the surface of the egg shell. In certain circumstances, some of these can pass through the shell and multiply within the egg, typically producing black, red or green rots. If such eggs are examined using a candling lamp, they will appear as dark, irregular patches.

External Egg Quality Faults Misshaped Eggs If albumen quality is very poor, there is no sound foundation upon which to build the true shell. The result can be the distinctive ‘crinkled’ shell typical of certain viral diseases. Misshaped eggs can also arise for other reasons. For instance, the shell may break in the shell gland during the formation process. The damage can be partly repaired but a bulge forms around the centre of the egg (an equatorial bulge). Any factor which causes disturbance to the birds 10-14 hours before the egg is laid is likely to increase the incidence of this fault.

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Section 0ne

Coated Shells Additional calcium may be deposited onto some eggs causing calcium splashing or a pink or lilac coloured egg. Typically these faults are caused by the egg remaining in the shell gland for an extended period. Often young flocks just coming into production are very susceptible to this and any stresses or disturbances at the time when the egg is due to be laid will encourage the bird to retain the egg.

Rough Shelled Eggs In some cases, two eggs may be in the shell gland at the same time and this can cause a form of rough shelled egg often referred to as a ‘target’ or ‘thumb-print’ type. This problem acn also result in ‘slab-sided’ eggs. There are other types of rough shelled eggs, including those with pimples or a sandpaper-type texture. Bird health and age often affect the incidence of this.

Pale Shelled Eggs Some of the egg shells laid by brown laying hens may be very pale or white in colour. The effect is purely cosmetic but such eggs may be rejected by certain customers. Older laying hens and disease conditions tend to increase the incidence of pale shells. There is also some evidence that pale shelled eggs are more common in free range flocks.

Soft and Weak Shelled Eggs Soft and weak shelled eggs can be common in older birds, especially those which are nearing the end of the laying period, having produced a high output of eggs. Where they are seen in younger flocks, they can be associated with coated or rough shells. If an egg is retained in the shell gland for too long, the next ovulation takes place at the usual time but before the previous egg is laid. The second egg may spend less time than normal in the shell gland and the result is a soft or shell-less egg. In such cases, a hen may not lay an egg on one day but may lay both a coated and a soft-shelled egg on the next.

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As a general point, it should be noted that a single stress or disturbance to a flock of laying hens can be enough to desynchronise the processes of egg formation for several days. This can cause a prolonged effect upon egg quality and during this time, a number of different egg quality faults may be seen. Inadequate nutrition can also lead to inferior egg shell quality. An egg shell contains around six grams of calcium carbonate and adequate daily supplies are needed. The laying hen has a particular requirement for calcium at the time when the egg is in the shell gland. If calcium supplies are not maintained, then shells will become progressively thinner and egg production may decline or cease. Temporary thinning of the egg shell may occur during periods of high temperature (above around 25°C) since feed intake is reduced. The shells quickly regain normal thickness when temperatures are reduced and feed intake increases.

Cracked Eggs Egg shells can easily be damaged after the egg is laid and cracking is one of the most common reasons for downgrading. It may be due either to an inadequate egg shell being laid or to poor handling which may occur during collection, grading or transportation. Three main types of cracks are identified: Hairline cracks are the most difficult to identify, particularly in very fresh eggs. Skilled candling is needed together with ideal working conditions. Hairline cracks are often caused by an egg colliding with an inflexible surface. Star cracks may often be visible under normal light although they are more easily seen during candling. A central point of impact may be seen and star cracks are often due to collisions between eggs. Pinhole and toehole cracks can be caused either by the birds themselves or by any sharp protrusions which may come into contact with the egg. There is evidence that a fault which appears similar may occur before the egg is laid.

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Section One

Dirty and Glazed Shells After the egg is laid, it can become affected with numerous contaminants including faecal material, dust, mud and litter (in non-cage systems), blood and the contents of other eggs. The latter is often referred to as glazing or varnishing. All of these lead to eggs being downgraded and high standards of hygiene and management, coupled with appropriate diet formulation and pest control must be maintained.

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4 Co m po s it io n & n ut r ie n t co nt e n t o f e gg s Composition On a weight basis, the egg consists of around 11% shell, 58% albumen and 31% yolk. Minor variations do occur due to factors such as breed, age of bird, nutrition and disease. Table 1 gives the approximate physical composition of a newlylaid egg. The proportion of the thick to thin albumen varies greatly, even in newly laid eggs due to factors such as bird age and health. Sometimes, even newly laid eggs contain little or no thick albumen.

Shell

11% True Shell Membranes

97 3 100

Albumen

58% Chalazae

3

Inner Thin

17

Outer Thick

57

Outer Thin

23 100

Yolk

31%

Table 1 Percentage physical composition of the egg

Nutrient Content The typical gross chemical composition of the edible part of an egg is summarised in Table 2. It is possible to change the quantity of certain nutrients in eggs by changing the diet of the laying hen. For example, the amount of polyunsaturated fatty acids can be increased at the expense of saturated fat. Similarly it is also possible to enrich eggs with additional vitamins and minerals if required.

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Section One

Whole Egg

Albumen

Yolk

Water (g)

75.1

88.3

51.0

Protein (g)

12.5

9.0

16.1

Fat (g)

10.8

Trace

30.5

Carbohydrate (g)

Trace

Trace

Trace

Energy Value (kJ)

612

153

1402

Table 2 Composition of eggs per 100 grams (excluding shell)

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5 E ffe c t s of st o r ag e u po n egg quality Immediately after the egg is laid, the internal contents and structure begin to change. This is a continual, irreversible process and even the most carefully controlled storage conditions can do no more than slow down the rate of deterioration. The main changes which occur are outlined below.

The Air Space When the egg is laid, it is warmer than its surroundings. As it cools, the contents contract and a small air space is formed between the inner and the outer shell membrane. The air space normally (but not always) forms at the broad end of the egg because there are more pores in this part of the shell. As the egg ages, moisture and carbon dioxide continue to be lost through the pores. Air moves in and the air space increases in size at a rate which is determined by the temperature and the relative humidity of the surrounding air. The warmer and drier the air, the quicker the moisture loss from the egg. The size (height) of the air space is used as an approximate guide to the quality and age of an egg.

Albumen Quality In a very fresh, good quality egg, the albumen is jelly-like and may have a cloudy appearance. As the egg ages and carbon dioxide is lost through the shell, the contents become more alkaline and this causes the albumen to become transparent and increasingly watery. At higher temperatures, the rate of carbon dioxide loss is higher and the visible signs of ageing occur quicker. The quality of albumen can be assessed by measuring the height in millimetres of the outer thick albumen. The height of the albumen and the weight of the intact egg is used to calculate the Haugh Unit value. Mottled yolks

It is the proteins in the thick albumen which begin to break down during storage as the egg becomes more alkaline. At the same time, water slowly migrates into the yolk and the shell from the albumen so that both may develop a mottled appearance and the yolk becomes enlarged and flattened on breakout. The yolk moves away from the centre of the egg and may eventually

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1 G r adi ng of e gg s f or h u ma n c on s um p ti o n rest against the shell itself. This breakdown of the albumen makes the egg extremely vulnerable to microbial invasion. Eggs are food. Like all foods, they must be assessed for quality to ensure that they are acceptable to the customer. Failure to remove defective eggs can lead to complaint, loss of business and prosecution. Every day, over 26 million eggs are produced in the UK. Successful quality control requires a combination of skill, concentration and practice. Gradually, automatic and mechanical developments have emerged which have reduced reliance on the human eye. However, much of this technology is currently affordable only to larger businesses and even when used, there is a need for supporting visual quality checks.

Class A egg – external

2 Q u a lit y sta n d a rd s – T h e E U m ar k e ti n g r eg u la t io n s a nd o t he r co nt ro ls A formal inspection must be undertaken so that each egg can be allocated to a particular Quality Class. These Classes are defined in the EU Egg Marketing Regulations which are enforced throughout all European Union (EU) countries. There are three quality classes for eggs intended for human consumption. In brief, these are:

•

Class A (‘fresh eggs’). These may further be sold as ‘Extra’ Fresh if the air space is less than 4mm in height at the time of candling and throughout its marketable seven days from packing.

• •

Class B (‘certain second quality or preserved eggs’). Class C (‘non graded eggs intended for the manufacture of foodstuffs for human consumption’). Class A egg – internal

Table 3 (see p18) provides further details of the minimum permissible standards for each Class.

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In practice, Class B eggs are seldom marketed and the main classes are A and C. All eggs sold in UK supermarkets and similar retail shops will be Class A. Class C eggs are normally sent to processing plants for pasteurisation. Any egg which fails to meet the Class C criteria is unfit for human consumption and is classed as an ‘Industrial Egg’. Typically, eggs with broken shells (i.e. where the shell membranes have been broken) fall into this category. Industrial eggs can be used for non-food uses if suitable markets can be found. Class A

Class A egg

Class A egg (extra fresh)

Cuticle

Normal, clean, undamaged

Shell

Normal, clean, undamaged

Air Space

Height not exceeding 6mm (4mm for Extra Fresh) Stationary

Albumen

Clear, limpid, of a gelatinelike consistency, free of all foreign bodies of any kind

Yolk

Visible on candling as a shadow only, without clearly discernible outline, not moving appreciably away from the centre of the egg on rotation, free from all foreign bodies of any kind

Germ Cell

Imperceptible development

Smell

Free of foreign smell

Wet or dry cleaning

Not permitted

NOTES (for guidance only)

Table 3 Minimum quality standards for eggs of Classes A, B and C

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In some cases, certain customers may impose their own buying requirements which exceed the minimum Class A standards. These may relate to the colour of the shell, the condition of the albumen (e.g. a minimum Haugh Unit score) or any other aspect of quality. Where this is the case, it is up to packing centres to incorporate these requirements into their normal inspection procedures.

Class B

Class C

Dirty, damaged, treated

Dirty, damaged, treated

Normal, undamaged

Cracked, misshaped, rough textured or any other abnormality

Height not exceeding 9mm Mobile

Height exceeding 9mm or damaged

Clear, limpid, free of all foreign bodies of any kind

Clear, no discolouration or turbidity, small foreign bodies permissible

Visible on candling as a shadow only, free from all foreign bodies of any kind

Distinct on candling, ‘sided’ or, ‘stuck’, no discolouration, small foreign bodies permissible

Imperceptible development

Imperceptible development

Free of foreign smell

Free of foreign smell

Permitted

Permitted

This category includes naturally dirty shelled and washed eggs

This category includes various shell faults and dry cracked eggs (membranes unbroken)

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Class A

Class B

Class C

Cuticle

Normal, clean, undamaged

Dirty, damaged, treated

Dirty, damaged, treated

Shell

Normal, clean, undamaged

Normal, undamaged

Cracked, misshaped, rough textured or any other abnormality

Air Space

Height not exceeding 6mm (4mm for Extra Fresh) Stationary

Height not exceeding 9mm Mobile

Height exceeding 9mm or damaged

Albumen

Clear, limpid, of a gelatine-like consistency, free of all foreign bodies of any kind

Clear, limpid, free of all foreign bodies of any kind

Clear, no discolouration or turbidity, small foreign bodies permissible

Yolk

Visible on candling as a shadow only, without clearly discernible outline, not moving appreciably away from the centre of the egg on rotation, free from all foreign bodies of any kind

Visible on candling as a shadow only, free from all foreign bodies of any kind

Distinct on candling, ‘sided’ or, ‘stuck’, no discolouration, small foreign bodies permissible

Germ Cell

Imperceptible development

Imperceptible development

Imperceptible development

Smell

Free of foreign smell

Free of foreign smell

Free of foreign smell

Wet or dry cleaning

Not permitted

Permitted

Permitted

This category includes naturally dirty shelled and washed eggs

This category includes various shell faults and dry cracked eggs (membranes unbroken)

NOTES (for guidance only)

Table 3 Minimum quality standards for eggs of Classes A, B and C

3 Q ua l i ty c o nt ro l m e t ho ds f o r e g gs A number of common quality faults can be seen by close inspection of eggs under normal lighting conditions. However, candling can reveal many other defects which may otherwise not be visible. For 70 years, egg candling has played a fundamental role in the marketing of eating eggs in the UK. The technique takes its name from the original source of light used – the candle. A beam of light is shone through the shell so that the contents become visible. The limitations of candling have long been recognised, but for many years, it provided the best way of identifying hairline cracks in shells and the only way of identifying internal faults without breaking the shell. Recently, automatic in-line detection equipment for cracked eggs and other faults has been developed and is now in use in larger packing centres to assist quality control staff. Inspection of eggs in commercial packing centres can be divided into individual egg and mass egg systems. The objectives and methods used are summarised below. Automatic crack detection unit (Picture reproduced by kind permission of Moba)

Individual Egg Quality Control Systems In many packing centres, eggs are graded from a large number of different flocks and it is important to get an overall assessment of the quality of each consignment before grading. The results obtained from testing a small sample of eggs can be used to determine the order of grading, the customer, the grading speed and the number of inspection staff needed. Assessments can be made by Individual (or Hand) Candling or by Break Out and related Laboratory Tests. In many cases, both tests will be undertaken.

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Individual (Hand) Candling In very small enterprises, hand candling may be the most cost effective way of assessing the quality of all eggs. In larger businesses, it is used to identify levels and types of faults in representative samples of ungraded and graded eggs. It is a condition of the EU Egg Marketing Regulations that grading equipment should include an independent candling lamp.

Candling Lamp Design A typical design of candling lamp is shown here. The key design features are that:

• •

the light should be focused onto the aperture.

•

the aperture should not exceed 30mm in diameter.

cushioning material should be fitted around the aperture to minimise leakage of light when the egg is in place.

Hand Candling Techniques

•

Direct the aperture away from the eye of the candler to avoid glare.

•

Keep the background in the candling area as dark as possible.

•

Hold the broad end of the egg to the aperture and then turn the egg so that all the surface area has been seen.

•

The visibility and movement of the yolk and any internal faults should be observed as the egg is turned.

•

A standard record sheet should be used to enter the number and type of faults.

For maximum speed of candling, the operator should aim to hold two eggs in each hand at a time. MAFF Egg Marketing Inspectors and ADAS offer training courses on the techniques used.

Break-Out/Laboratory Tests In order to provide more detailed information on aspects of quality and consumer preference, break-out and other laboratory tests are undertaken on representative samples of eggs.

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Hand candling of eggs

Typical consumer preferences include freshness, shell and albumen quality and shell and yolk colour. At best, candling and other visual assessments can provide a guide but more detailed measurements are needed to ensure that customer needs are met. Detailed break-out tests take time to complete and because the tested eggs are unsaleable, only small numbers can be used. Eggs from a single flock of a given age are reasonably consistent and so a fairly small sample can provide a useful indication to the average quality of eggs from the whole flock. Equipment for measuring the shell and yolk colour and shell and albumen quality is now commercially available and used widely within UK packing centres. All measurements can be automatically recorded and compared with standard and target figures.

Mass Egg Inspection As the scale of individual businesses has increased and technology has advanced, so the methods used have changed.

Modern equipment for measuring egg quality (Picture reproduced by kind permission of TSS Technical Services and Supplies (York))

Traditional commercial machines may grade around 100 cases of eggs (3,000 dozen) per hour. In the largest packing centres, up to 300 cases of eggs may be graded per hour on a single machine. The higher throughput machines generally incorporate more automation so that identification of faults and segregation of second quality eggs is easier. At the packing centre, mass egg inspection normally takes place in two stages. First of all, an initial pre-candling or pre-selection takes place, followed by the main candling process.

Pre-Candling Procedures The aim of pre-candling is to remove eggs with visible faults. In particular, it should succeed in removing gross faults such as eggs with dirty, glazed (wet), weak, coated, badly cracked or

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misshaped shells. A particular priority is to remove eggs with faults which may contaminate other eggs. The main requirements for successful pre-candling are as follows:

•

It should take place shortly after the eggs have been loaded.

•

Eggs should be viewed under normal but high intensity light.

•

It should be possible for the pre-candler to see the majority if not all of the surface of the egg.

•

The number of pre-selection staff needed and the throughput speed should be determined by the expected quality of the incoming eggs.

•

A comfortable working environment and regular breaks are needed if high standards are to be maintained.

•

Pre-candling staff should be suitably trained and their performance regularly assessed.

Mass Egg Candling Egg candling is an immensely difficult task which requires skill, practice and concentration. Eggs pass through the booth in parallel rows on rollers. A single candler working on a 100 cases per hour grading machine has to inspect 10 eggs per second and remove perhaps one of them. Candling should be seen as one part of a larger inspection process at the packing centre. The starting point is pre-candling. If effective, this allows more attention to be placed on faults which cannot be seen under normal light, such as ‘hairline cracks’ and internal faults.

(Picture reproduced by kind permission of Moba)

Candling Facilities

•

Successful candling requires an enclosed booth, free from external light.

•

Eggs should be illuminated from beneath using high intensity lighting.

Commercial scale egg candling

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•

A mirror should be incorporated and so positioned as to enable the candler to see both ‘poles’ of each egg.

•

Both the mirrors and the covers over the lights must be kept clean and dust-free to ensure good visibility.

•

The candler should be able to work (whether standing or sitting) in surroundings which are comfortable and the height of the platform or seat should be adjustable according to the height of the candler.

Candling Personnel

•

Candlers should have good eyesight and should be encouraged to have regular eye examinations.

•

Regular breaks from candling are essential and no one should be required to spend more than 30 minutes in the booth at any one time.

•

Candlers should not be expected to perform any other tasks whilst in the booth.

Candling Procedures

•

To reduce glare from the lights, a throughput of eggs should be maintained which ensures that the rollers are as full as possible.

•

The throughput speed of the grader must be geared to the quality of eggs being assessed and the parameter speeds for correct ink-jetting onto egg shells where fitted.

•

If the rollers become wet due to broken eggs, the grader should be stopped so that cleaning can take place.

•

The candler should concentrate on the eggs within a particular small zone within the booth and eggs within that zone should be examined in a logical sequence, with the mirrors being used as necessary.

•

If in doubt, an individual egg should be removed from the rollers and examined more closely at a convenient moment.

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•

In addition to shell faults, the experienced candler should be able to assess: – the size and position of the air space – the appearance and movement of the yolk (which provides an indication of albumen quality) – whether the egg contains inclusions such as blood or meat spots.

•

In conventional systems, eggs with faults must be removed by hand and put onto conveniently placed keyes trays or into buckets.

•

In semi-automated, higher throughput systems, eggs identified as seconds may be electronically marked by the candler so that they are automatically diverted to the seconds lane.

•

In systems which include automatic detection of cracks and certain other faults, the candler is free to concentrate on other aspects of quality which require visual identification.

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Gl os s a ry of t e rms Air Space The space which forms between the inner and outer shell membranes as a result of air movement through the egg shell pores. The size of the air space increases during storage. Albumen Also known as ‘egg white’ it is rich in protein and vitamins and provides support and protection for the yolk. Candling A quality control procedure which allows assessment of internal egg quality and easier identification of certain other faults, particularly hairline shell cracks. Chalazae Twisted, fibrous structures which extend outwards through the albumen and hold the yolk in place in the centre of the egg. Clutch A sequence of daily egg laying by an individual bird which is separated from other sequences by one or more ‘pause days’ on which no eggs are laid. Cuticle The outer coating of the egg shell which gives the egg its characteristic bloom or shine. Germ Cell (Germinal Disc) Sometimes identified on the surface of the yolk as a disc of slightly different colour, the germ cell is the site of cell division if the egg has been fertilised. Grading The classification of eggs by Quality (Classes A, B, C and Industrial) and into weight bands as defined by EU Egg Marketing Regulations. Haugh Unit A measurement made to determine albumen quality. The Haugh Unit is calculated from the height of the thick albumen and the weight of the intact egg.

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Section Three

Ovary The reproductive organ of the laying hen in which the egg yolks develop. Oviduct A long tube-like organ in the laying hen which accepts the yolk after ovulation and is responsible for the remainder of the egg formation process. Oviposition The name for the process of laying an egg. Ovulation The release of the yolk from the ovary into the oviduct. Ovum (plural: ova) Commonly known as the yolk, the ovum consists of the vitalline membrane, the germ cell and the yolk material. Pores Tiny holes in the egg shell which permit movement of air and moisture between the egg and its surroundings. Shell The outer covering of the egg which is largely composed of calcium carbonate. Shell Gland The part of the oviduct which is responsible for shell formation. Shell Membranes The innermost part of the egg shell (visible in so-called ‘shellless eggs’) which acts as the foundation upon which the true shell is built. Vitalline Membrane A see-through barrier which surrounds and contains the yolk. Yolk Consists of fats, vitamins and minerals and about half of the egg’s total protein content.

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P ic t o ri a l g u id e t o eg g qu al i t y Freshness and albumen quality

1

Class A Egg

Class A Egg showing air space < 6mm

2

3

Extra Fresh Class A showing air space < 4mm

Class B Egg showing air space > 6mm

4

5

Egg with good quality, gelatinous albumen

Egg with watery albumen

6

28

Section Four

Shell faults

7

Shell-less Egg

Soft-shelled Egg

9

Target or Thumb-print Type

Slab-sided Egg

10

Crinkled Shell

12

11

Equatorial Bulge

8

29

Shell faults (cont’d)

13

Rough Shell

15

Calcium Splashed

30

Pale Shell

14

Lilac/Pink Shell

16

Section Four

Cracked eggs

17

Star Crack

19

Pinhole Crack (Candled)

Star Crack

18

Hairline Crack

20

31

Dirty eggs

21

Faeces

Urate

22

23

Oil/Tar

Blood

24

25

Glazed or Varnished with Yolk

Glazed or Varnished with Albumen

26

32

Section Four

Internal quality

27

Typical Range of Yolk Colours

29

Mottled Yolk

31

Meat Spot

Double Yolked Egg

28

Internal Mould (Microbial Invasion)

30

Meat Spot in Intact Egg

32

33

Internal quality (cont’d)

33

34

Blood spot

Mobile airspace

32

PB XXXX (Fu rther copies availabl e from M AFF Publications, Admail 6000, London SW1A 2XX

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