Preservation of Food

Preservation of Food

Food needs to be preserved...

  • So that surplus foods from good harvests can be stored and then used in times of shortage.
  • So that we can enjoy seasonal fruits and vegetables all year round.
  • To enable it to be transported long distances without it decaying (and spillage!)
  • To allow it to be stored in the home for long periods without going off.

There are many ways in which food can be preserved. The method chosen will depend on commercial considerations, such as costs, as well as the type of food that needs to be preserved.

There are six main ways in which food can be preserved...

Preservation of Food

1. High temperatures

  • Canning
  • Bottling
  • Pasturisation
  • Ultra Heat Treatment(UHT)
  • Sterilisation
Preservation of Food

2. Low temperatures

  • Freezing
  • Chilling
Preservation of Food

3. Removing moisture

  • Drying
  • Accelerated Freeze Drying (AFD)
Preservation of Food

4. Use of chemicals

  • Pickling
  • Salting
  • Smoking
  • Sugar
Preservation of Food

5. Controlling the atmosphere

  • Vacuum packing
  • Modified atmosphere packaging (MAP)
Preservation of Food

6. Irradiation

Method and How it works: Advantages: Disadvantages: Used for:
Canning: Heat kills bacteria and enzymes. Lasts for many years. Can cause changes in colour and texture. Loss of Vitamin C. Fish, meat, fruit, vegetables, milk.
Bottling: Heat kills bacteria and enzymes. Lasts for many years. Can cause changes in colour and texture. Loss of Vitamin C. Fruit and vegetables.
Pasteurisation: Most bacteria killed at 72 degrees Celsius. Little effect on flavour. Not all bacteria killed. Milk, cream, orange juice.
UHT: All bacteria killed at 132 degrees Celsius. Lasts for several months. Changes taste slightly. Milk, fruit juices.
Sterilisation: Food is heated to 104 degrees Celsius for 40 minutes. Extends life of milk to about 10 days. Gives a creamy flavour and colour. Milk, fruit juices.
Freezing: Stops bacteria and enzymes activity. Domestic freezers are at -18 degrees Celsius. Foods can be frozen for many months. Little loss of vitamins. Slow freezing breaks down cells and changes the texture of foods. Ready prepared meals, fish, meat, vegetables, fruit, ice-creams.
Chilling: Temperatures of 1 to 8 degrees Celsius slow bacteria growth. Good colour and flavour kept. Short storage life. Ready prepared meals, such as Lasagne.
Drying: Removal of moisture stops bacteria growth. Last for long periods of time. Most Vitamin C lost. Must be kept dry. Soups, pasta, beans, packet desserts.
AFD: Food is frozen and then dried quickly. Good colour and flavour. Can be expensive. Coffee.
Pickling: Increases acidity of food. Long shelf life. Very strong flavour. Onions, cabbage, olives.
Salting: Reduces water content by osmosis. Long shelf life. Food needs to be soaked before cooking. Meat, fish, green beans.
Smoking: Slow method, which prevents bacteria growth. Adds flavour. Kills Vitamins B and C. Bacon, cheese, fish.
Sugar: More than 60% will stop micro-organism growth. Long shelf life. High temperatures in jam making kill Vitamin C. Jams, marmalade, crystallised fruits.
Vacuum packs: Removes all oxygen. Retains vitamins. Often still needs refrigeration Bacon, fish.
MAP: Replaces oxygen with nitrogen and carbon dioxide. Colour and flavour are good. Expensive. Meat, salads, minced beef, and bacon.
Irradiation: Radiation kills, bacteria and pests. Delays ripening of fruit and sprouting of vegetables. Not in general use. Consumer safety worries. Strawberries, vegetables and spices.