Grade 3 Science (NSO) : Food part 3 – Preservation of food

Food Decay and Preservation

Bacteria and fungi are the main groups of  decomposer organisms. Food decay is also known as food spoilage.

Bacteria and fungi need Food , Warmth and Moisture to grow.

There are several ways to stop or slow down the decay of foods. This is known as Food Preservation.


Food preservation methods


Bacteria cannot reproduce at low temperatures.

Bacteria and fungi need warmth to grow. In low temperatures they stop growing.

Following is the list of food preserved by freezing;

  • Meat
  • Fish
  • Fruits
  • Vegetables
  • Fresh foods
  • Cooked foods


Removing water prevents the microorganisms from growing, or digesting the food.


  • Fruit
  • milk
  • soups,
  • pasta
  • cereals
  • beans


The sealed can is heated to kill bacteria. When it cools, no more bacteria can enter.

Examples :

  • Fruits
  • Vegetables


Vinegar, used in pickles, is too acidic for bacteria and fungi to be able to grow.

Adding sugar

Removes water by osmosis.

A lot of sugar is added to fruit to make jam, marmalade and jellies.

Adding salt

Salt absorbs water from foods, making the environment too dry to support harmful mold or bacteria.

A lot of salt is added to preserve fish.