Food Preservation – Year 6

What is Food Preservation?
Food preservation is the process of treating and handling food to stop or slow down spoilage (loss of quality, edibility or nutritional value) and thus allow for longer storage. Preservation usually involves preventing the growth of bacteria, yeasts, fungi, and other micro-organisms (although some methods work by introducing benign bacteria, or fungi to the food), as well as retarding the oxidation of fats which cause rancidity. Food preservation can also include processes which inhibit visual deterioration (when something becomes less close to the original) that can occur during food preparation; such as the enzymatic browning reaction in apples after they are cut.

Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit, by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). There are many traditional methods of preserving food that limit the energy inputs and reduce carbon footprint. Maintaining or creating nutritional value, texture and flavor is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. In many cases these changes have now come to be seen as desirable qualities – cheese, yoghurt and pickled onions being common examples.

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.
  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;
  • Emit an unpleasant smell
  • Have an unpleasant taste
  • Change color
  • Change in texture
  • Become mouldy
  • Become slimy

Micro-organisms Can Spoil Food

  1. The growth of micro-organisms such as fungi and bacteria can spoil food.
  2. Fungi and bacteria can grow wisely on damp foods that are exposed to the air.
  3. Fungi and bacteria change the food material into simple substances.
  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 micro-organisms are…
  • Water
  • Air
  • Nutrient
  • A suitable temperature and
  • Suitable acidity

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:

  • it keeps food for a longer time.
  • it kills bacteria and fungi

6. We preserve food by:

  • keeping it dry
  • keeping it hot or frozen
  • keeping it airtight

7. There are various methods of preserving food. They include:

  • drying
  • boiling/heating
  • cooling
  • vacuum-packing
  • pickling
  • freezing
  • bottling/canning
  • pasteurizing
  • salting
  • smoking
  • waxing

a. Drying
Drying consists in removing the water from a product. This can be done through heating, creating a vacuum or using chemicals that’ll absorb the water (e.g. concentrated sulfuric acid), or through slow progressive drying. This is a way of preserving food in so far as microbes can’t develop without water.

Dehydration is a particularly well adapted way of preserving herbs, fruits or even vegetables. Dehydration and lactic acid fermentation are the healthiest methods of food preservation as the vitamins are kept intact and rebuild themselves when the food is rehydrated. Besides, this sort of food is easy to carry (e.g. for holidaymakers) and medicinal herbs, they keep all their properties

There are solar dryers : especially useful for cold or temperate climates (Quebec…), though they can be used in Summer only, when nights get colder, drying is less easy as moist can penetrate the plant if there is no additional heating.

1. Drying involves the removal of water contained in the food. There are three ways of drying foods:

  • Drying food under the sun.
  • Drying food over fire (wood or charcoal fire) or oven.
  • 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 of water. The advantages and disadvantages are shown in the table below.

b. 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.

c. 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.

d. Vacuum-packing
Vacuum-packing stores food in a vacuum environment, usually in an air-tight bag or bottle. The vacuum environment strips bacteria of oxygen needed for survival, slowing spoiling. Vacuum-packing is commonly used for storing nuts to reduce loss of flavor from oxidation.

  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. Micro-organisms 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.

e. Pickling
Pickling is a method of preserving food in an edible anti-microbial liquid. Pickling can be broadly categorized as chemical pickling for example, in chemical pickling, the food is placed in an edible liquid that inhibits or kills bacteria and other micro-organisms. Typical pickling agents include brine (high in salt), vinegar, alcohol, and vegetable oil, especially olive oil but also many other oils. Many chemical pickling processes also involve heating or boiling so that the food being preserved becomes saturated with the pickling agent. Common chemically pickled foods include cucumbers, peppers, corned beef, herring, and eggs, as well mixed vegetables such as piccalilli. In fermentation pickling, the food itself produces the preservation agent, typically by a process that produces lactic acid. Fermented pickles include sauerkraut, nukazuke, kimchi, surströmming, and curtido. Some pickled cucumbers are also fermented.

  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. Micro-organisms cannot survive under acidic conditions.
  7. Unripe papaya, mango, nutmeg, chillies and some vegetables are suitable for pickling.

f. Freezing
Freezing is also one of the most commonly used processes commercially and domestically for preserving a very wide range of food including prepared food stuffs which would not have required freezing in their unprepared state. For example, potato waffles are stored in the freezer, but potatoes themselves require only a cool dark place to ensure many months’ storage. Cold stores provide large volume, long-term storage for strategic food stocks held in case of national emergency in many countries.

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

g. Bottling/canning
Canning involves cooking food, sealing it in sterile cans or jars, and boiling the containers to kill or weaken any remaining bacteria as a form of sterilization. It was invented by Nicolas Appert. Foods have varying degrees of natural protection against spoilage and may require that the final step occur in a pressure cooker. High-acid fruits like strawberries require no preservatives to can and only a short boiling cycle, whereas marginal fruits such as tomatoes require longer boiling and addition of other acidic elements. Low acid foods, such as vegetables and meats require pressure canning. Food preserved by canning or bottling is at immediate risk of spoilage once the can or bottle has been opened.

Lack of quality control in the canning process may allow ingress of water or micro-organisms. Most such failures are rapidly detected as decomposition within the can causes gas production and the can will swell or burst. However, there have been examples of poor manufacture (under processing) and poor hygiene allowing contamination of canned food by the obligate anaerobe Clostridium, which produces an acute toxin within the food, leading to severe illness or death. This organism produces no gas or obvious taste and remains undetected by taste or smell. Its toxin is denatured by cooking, though. Cooked mushrooms, handled poorly and then canned, can support the growth of Staphylococcus aureus, which produces a toxin that is not destroyed by canning or subsequent reheating.

  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.
  • The food is prepared and washed.
  • The food is placed in a can or a bottle.
  • The food is then heated by steaming to remove all the air.
  • The can or bottle is sealed immediately to make it airtight.
  • The can or bottle is heated by steaming to kill all micro-organisms.
  • The can or bottle is labelled and packed.
  • Pasteurizing
  1. Heating up food without boiling them can kill the micro-organisms in the food.
  2. To pasteurize fresh milk, it is heated at 65°C for 30 minutes or at 27°C 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.
  4. This method destroys harmful germs.

i. Salting
Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat and contribute the characteristic pink color, as well as inhibition of Clostridium botulinum.

  1. We can preserve food by adding a large amount of salt to the food.
  2. This is called salting.
  3. Micro-organisms such as bacteria and fungi cannot grow in very salty.
  4. In salty conditions the micro-organisms 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.

j. Smoking
Smoking is used to lengthen the shelf life of perishable food items. This effect is achieved by exposing the food to smoke from burning plant materials such as wood. Most commonly subjected to this method of food preservation are meats and fish that have undergone curing. Fruits and vegetables like paprika, cheeses, spices, and ingredients for making drinks such as malt and tea leaves are also smoked, but mainly for cooking or flavoring them. It is one of the oldest food preservation methods, which probably arose after the development of cooking with fire.

  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.

k. Waxing
Waxing of fruits and vegetables is done according to the recommendations. Food grade waxes are used to replace some of the natural; waxes removed in washing and cleaning operations, and this helps to reduce the water loss during handling and marketing. If produce is waxed, the wax coating is allowed to dry thoroughly before further handling. Waxing was used as a preservation technique for fruits.

  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:
  • the food will last longer
  • the food is easy to store
  1. The preservation of food enables uncooked meat to be distributed in frozen form to all parts of the world without lowering its quality.
  2. Preservation helps prevent wastage.
  3. Food preservation can help the nation’s economy by adding value to our export products.


Bottling – pembotolan
Canning – pengetinan
Cooling – pendinginan
Drying – pengeringan
Freezing – penyejukbekuan
Heating – pemanasan
Pasteurizing – pempasteuran
Pickling – penjerukan
Preservation – pengawetan
Salting – pengasinan
Smoking – pengasapan
Spoilage – kerosakan
Vacuum-packing – pembungkusan vakum
Waxing – pelilinan


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