You know that foods like milk, fruits, vegetables, meat and fish get spoiled very easily. When you leave milk on kitchen shelf for a few hours it curdles and starts giving a foul smell. Raw fruits and vegetables also become stale in a day or two. Curdling of milk occurs due to the action of bacteria. Thus, spoilage of milk, bread, meat, etc., occurs due to the action of microorganisms like bacteria and fungi.
Foodstuffs which have a greater water content like fruits, vegetables and milk get spoilt faster than those with less water content like wheat, rice and pulses. Rats, insects, bacteria and fungi, spoil food grains.
A considerable amount of food materials is thus lost in homes and during storage at trading centers like fruit and vegetable markets or fish market. Wastage of food items can be reduced by following certain methods or techniques that prevent the spoilage of food and help in retaining their nutritive value. Such methods or techniques are collectively called food preservation. Let us study some of the methods of food preservation.
1. Cleaning and storing in closed containers:
Food grains like rice, wheat and pulses should be cleaned first and then stored in closed containers. Keeping the food grains in closed containers protects them from micro-organisms, rats, cockroaches and other insects.
2. Sun drying and dehydration:
Microorganisms require water for their growth. Drying and dehydration mean removal of water from foodstuff. Sun drying involves removal of water by keeping the food articles in the sun. Vegetables like spinach, fenugreek (methi), cauliflower, etc., are sun-dried and stored. Potatoes, bananas, tapioca and cooked rice or dal are sun-dried to wafers or papads and stored for long periods.
Heating kills microorganisms. You boil milk at home to kill bacteria. Boiling water kills all germs and makes it safe for drinking.
4. Deep freezing:
Bacteria and fungi cannot grow at low temperatures. Refrigerators are used to keep fruits, vegetables, milk, butter, meat and fish fresh for a longer time. In huge freezers, food can be frozen and kept fresh for months together.
5. Using salt, sugar and vinegar for preservation:
Preservation of food by using salt is called salting. Salt can be used in the dry form or in the form of solution. It draws out water from food and prevents growth of microorganisms. Salt is used to preserve tamarind, beans, raw mango, amla, fish and meat. Fruits and vegetables like raw mago, amla, lemon, cauliflower, carrots, etc., can be made into pickles by adding salt, vinegar and oil. These substances prevent the growth of microorganisms.
6. Chemical preservation:
Certain chemicals preservatives are added to jams, jellies, juices and squashes to prevent the growth of microorganisms. Sodium benzoate and acetic acid are commonly used as preservatives.
In the canning process, fresh food is cooked quickly and is then put in a tin container and the container is sealed. The sealed container is then heated to kill all the microorganisms present inside.