What is food preservation about
What about food preservation:
Food is spoilt by the saprophytic activities of putrefying bacteria. Sometimes, the food becomes contaminated with highly poisonous bacterial excretions, as in “botulism”. Methods of preserving food attempt to reduce its bacterial content by removing at least one of the conditions essential for the survival of most living organisms.
- A water supply
- Oxygen
- A suitable temperature
The bacteria either die or are unable to reproduce.
Food Preservation Methods
In refrigeration, food is kept at temperatures too low for bacterial reproduction. Fruit can be preserved as jam. Here, a sugar solution of high concentration draws water out of the bacteria by osmosis: the bacteria die by dehydrating.
The same process occurs when meat is preserved in brine, a concentrated solution of salt.
Dried fruit is preserved similarly, because the sugar in the fruit becomes very concentrated when the fruit dries.
Canning, suitable for a wide variety of foods, attacks the bacteria in two ways. The high temperatures used (up to 1200C) kill both bacteria and their spores; the cans are quickly cooled and vacuum-sealed, so that there is very little air and no more bacteria can enter.
Bacteria cannot survive in acid conditions: pickling is used to preserve certain foods whose flavour, though altered is not spoilt by the acetic acid (in vinegar).
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Pasteurization delays the souring of milk. Milk is heated to about 700C and quickly cooled. Some bacteria are killed: the growth of others is retarted. Boiling milk (sterilization) kills more bacteria, but alters the flavour.