By Ajay Anand
Techniques to prolong the shelf life of a food are called food preservation.
Microbes proliferate very fast in presence of food, moisture, oxygen and ambient temperature.
Sun-drying helps in removing moisture from food.
Grains are dried in sun before being stored.
Many vegetables are also sun-dried so that they can be used in off season.
Some chemicals prevent the growth of microorganisms in food.
These chemicals are used in pickles and jams to preserve them.
Salt, acids and oil are also used as food preservatives.
When a food item is kept in plenty of salt, water from food comes out because of osmosis.
It results in dehydration of the food item.
Absence of moisture helps to prevent the growth of microbes.
Fish, meat and pickles are preserved by adding salt.
The layer of oil on top of food prevents oxygen from entering the food.
Some microbes do not survive in absence of oxygen.
Some microbes cannot survive in acidic environment.
So, vinegar is an effective food preservative.
Most of the organisms can survive within a particular range of temperature.
When the temperature becomes too low or too high, organisms cannot survive.
Heating a food item or freezing a food items thus helps in preservation.
This method was discovered by Louis Pasteur.
Pasteurization involves heating the milk to 70°C for about 15 to 30 seconds and is then quickly cooled down.
Pasteurization helps in killing the microbes which may be present in milk.
Some food items are stored in air-tight packets.
Some food items are packed in cans, along with some preservatives.
Oily food (such as potato chips) is packed in air-tight packets which are filled with nitrogen gas.