Food Preservation

Food Preservation Food Spoilage 1. Our food comes from animals and plants. 2. Fresh products such as fruits, milk and vegetables do not last long if kept at room temperature. 3. Food turns bad because of bacteria and fungi.

Some examples of spoilt food.

4. However, not all bacteria and fungi are harmful. 5. When food spoilt, it usually changes in appearance.

6. The action of bacteria and fungi causes spoilt food to; (a) emit an unpleasant smell (b) have an unpleasant taste (c) change colour (d) change in texture (e) become mouldy (f) become slimy

The characteristics of spoilt food.

Microorganisms Can Spoil Food 1. The growth of microorganisms such as fungi and bacteria can spoil food. 2. Fungi and bacteria can grow easily on damp foods that are exposed to the air. 3. Fungi and bacteria change the food material into simple substances.

Bacteria and fungi 4. These simple substances may be poisonous. 5. Spoilt food is unsafe to eat because it contains poisonous substance. 6. We can get food poisoning if we eat spoilt food. 7. Eating spoilt food can also cause bacterial and fungal infections. 8. The conditions suitable for the growth of microorganisms are... - water - air - nutrient - a suitable temperature and - suitable acidity 9. Bacteria and fungi cannot grow if there is no air. 10. Bacteria and fungi can grow easily in damp and warm conditions. 11. Bacteria and fungi get killed at high temperatures. 12. Bacteria and fungi cannot grow if there is no water.

13. Bacteria and fungi cannot grow in a very acidic or very alkaline medium.

14. Vinegar is a very acidic solution.

Food Preservation 1. We can prevent food from going off or at least delay it. 2. We must preserve it. 3. We preserve food to make it last longer. 4. Food preservation is a process of slowing down the decay of food. 5. Food preservation is important because: (a) it keeps food for a longer time. (b) it kills bacteria and fungi 6. We preserve food by: (a) keeping it dry (b) keeping it hot or frozen (c) keeping it airtight 7. There are various methods of preserving food. They include: (a) drying (b) boiling/heating (c) cooling (d) vacuum-packing (e) pickling (f) freezing (g) bottling/canning (h) pasteurizing (i) salting (j) smoking (k) waxing

Drying 1. Drying involves the removal of water contained in the food. There are three ways of drying foods: (a) Drying food under the sun. (b) Drying food over fire (wood or charcoal fire) or oven. (c) Passing food through hot air to extract the water content. 2. Examples of food preserved by drying are prawns, fish and cuttlefish.

3. We can make this process more effective by adding salt to the food before it is dried. 4. The dried food can be kept longer because microorganisms cannot grow due to lack water. 5. The advantages and disadvantages are shown in the table below.

Boiling/heating

1. Heat can kill various microorganisms that can cause food turn bad. 2. Heat can be used to sterilize food. 3. When food is boiled, cooked, fried or grilled, the bacteria present in the food are killed.

Cooling 1. Food can be preserved by storing it in a cool place such as refrigerator. 2. In cool conditions bacteria become less active a do not reproduce or give off poisonous gases. 3. Fruits and vegetables are examples of food that can be kept longer in cool temperatures. 4. Low temperatures do not kill the bacteria and fungi, but it slows down their growth.

5. Examples of food preserved by cooling

Vacuum-packing 1. In this method of preservation, food is sterilized before it is packed in air-tight containers or packages, depending on the type of food. 2. Air from the packages and containers are drawn out to make a vacuum. 3. Microorganisms cannot survive without air as they require air for respiration. 4. Examples of food preserved by vacuum-packing are biscuits, peanuts, coffee powder and crackers. 5. Examples of fruits that are preserved by vacuum-packing are bananas, pineapples and corn.

Pickling 1. Pickling is done by soaking food in vinegar, salt solution or sugar solution. 2. Pickling reduces the water content in food. 3. This prevents the growth of bacteria and fungi. 4. Food preserved by pickling will keep longer. 5. However, its taste and nutrient content will be different. 6. Microorganisms cannot survive under acidic conditions. 7. Unripe papaya, mango, nutmeg, chilies and some vegetables are suitable for pickling.

Freezing 1. Meat, poultry and fish are examples of food that are normally preserved by freezing. 2. Freezing is kept frozen at a temperature -10oC. 3. The colder the environment, the slower the growth of microorganisms. 4. The microorganisms become inactive but they are not killed. 5. The microorganisms become active again at room temperature. 6. Food that can be preserved by freezing is chicken, meat, prawns and cuttlefish. 7. Freezing preserves the quality and nutrient content of the food.

Bottling/canning 1. We can also preserve food by putting it in airtight cans or bottles. 2. Food can keep very long if kept in airtight cans or bottles. 3. The food is cooked before it is canned or bottled. The air within is removed before the container is sealed. Growth of bacteria and mould is prevented due to the lack or air. 4. Foods that can preserve by canning or bottling include meat, fish, fruits and vegetables.

5. Diagram below shows the steps in the bottling process.

1. The food is prepared and washed.

2. The food is placed in a can or a bottle.

3. The food is then heated by steaming to remove all the air.

4. The can or bottle is sealed immediately to make it airtight.

5. The can or bottle is heated by steaming to kill all microorganisms.

6. The can or bottle is labeled and packed.

Pasteurizing 1. Heating up food without boiling them can kill the microorganisms in the food. 2. To pasteurize fresh milk, it is heated at 65oC for 30 minutes or at 27oC for 15 seconds. Then, the milk is cooled down quickly and packed into sterile containers. 3. Pasteurization retains the original flavour and taste of food.

Food preserved through pasteurisation 4. This method destroys harmful germs.

Salting 1. We can preserve food by adding a large amount of salt to the food. 2. This is called salting. 3. Microorganisms such as bacteria and fungi cannot grow in very salty. 4. In salty conditions the microorganisms will lose water and shrink. 5. We can make this process more effective by drying the salted food. 6. Examples of food that can be preserved by salting are vegetables, meat, fish and eggs.

Smoking 1. Smoking is a natural food preservation technique. 2. Food is hung over a fire to dry it. 3. The smoke will dry the food but does not cook it. 4. This smoke also changes the taste of the food. 5. Meat produce is smoked in order to preserve it. 6. The meat is soaked in a solution of salt. 7. Then, it is slowly cooked over a flameless fire where only smoke is emitted. 8. This method is used for foods that are eaten raw such as beef fillets or smoked fish. 9. This method is also used to preserve fruits such as bananas and dates.

Waxing 1. We can preserve food by covering with wax. This process is called waxing. 2. The wax is obtained from plants, beef fat and petroleum. 3. Waxing help to slow down the loss of water from fruits and vegetables. 4. Waxing also give a gloss to the skin and makes the fruits and vegetables more shiny. 5. However, waxing can be harmful to humans. 6. Even washing in hot water cannot remove the wax from the waxed food.

The Importance Of Preserving Food 1. Food can keep long if it is preserved. 2. Spoilt food cannot be eaten. It will cause food poisoning with symptoms such as vomiting and diarrhea. 3. The preservation of food brings about many advantages to humans. 4. Advantages of preserved food: (a) the food will last longer (b) the food is easy to store 5. The preservation of food enables uncooked meat to be distributed in frozen form to all parts of the world without lowering its quality. 6. Preservation helps prevent wastage. 7. Food preservation can help the nation's economy by adding value to our export products.