The process by which spoilage of food is prevented using suitable chemical or physical methods is called food preservation. Some of these methods are given below
(i) Chemical method The chemicals used to check the growth of microorganisms are called preservatives. Salts, edible oils and acid preservatives are added to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives used to check the growth of microbes. They are added in jams and squashes to check their spoilage.
(ii) Preservation by common salt It has been used to preserve meat and fish for ages. Salting is also used to preserve amla, raw mangoes, tamarind, etc.
(iii) Preservation by sugar Jams, jellies and squashes are preserved by sugar. It reduces the moisture content which inhibits the growth of bacteria which spoil food.
(iv) Preservation by oil and vinegar Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are preserved by this method.
(v) Heat and cold treatments Boiling kills many microorganisms. Similarly, we keep our food in the refrigerator as low temperature inhibits the growth of microbes.
(vi) Pasteurisation It is used for the preservation of milk. It involves the process of heating milk to about 70°C for 15 to 30 seconds (killing most of bacteria) and then cooling it quickly at a very low temperature. This milk is then stored in cold temperature. Pasteurised milk can be consumed without boiling as it is free from harmful microbes. The milk that comes in packets does not get spoiled as it is pasteurised. The process of pasteurisation was discovered by Louis Pasteur.
(vii) Storage and packing These days dry fruits and even vegetables are sold in sealed air tight packets. This helps to preserve food by keeping germs and microbes out. Airtight packets also prevent food from moisture and contamination.