Due to excessive heat, heat, moisture, insect, bacteria, yeats and defective storage, the cooked food, fruits and vegetables are spoiled. If food is kept for a long time, germs start growing in it. The food starts rotting and the spoiled food looses flavor, taste and becomes unfit for eating. If food is kept in a refrigerator then the growth of germs slows down.
Sometimes cooked and uncooked foods are preserved to be used later. This is called food preservation.
Some common methods of food preservation are given below:
(i) Boiling and canning: We boil some of the food items. Boiling kills germs and thus, boiling makes the food germ-free. This germ-free food is stored in air-tight containers called cans. This method is called canning. The combined method of boiling and canning is widely used. For example, foods like meat, fish, syrup, soda water, liquid medicines, etc. are preserved by this method.
(ii) Storing at low temperature: Food kept in a cool place remains fresh for a longer time. At home, we store cooked food, fruits, vegetables, meat, eggs, cold-drinks, etc. in a refrigerator. Deep freezers are used to store food for much longer period. Often potatoes, vegetables and fruits are stored in a cold storage to keep them fresh.
(iii) Drying and dehydrating: Germs do not grow in dry and dehydrated food. So if food is dehydrated and its water is completely removed, it can be preserved for many days. Dehydrated peas, condensed milk, etc. remain good for a long period.
(iv) Salting: Common salt is used in food preservation. Pickles are preserved by using salt and oil. Meat, fish, vegetables are also preserved in this way.
(v) Adding sugar: Food is also preserved in strong sugar-syrup. Jam, jelly, etc. are preserved in this way.
Storage of germs: Food-grains are spoiled by rats, insects and moisture. So they should be stored properly to keep them for a long time.
(a) Food-grains should be sun-dried first and then stored in air-tight containers.
(b) The stored food-grains should be free from insects. These grains should be placed in such a way that they may be saved from rats and insects.