Food Preservation by Canning

Food Preservation by Canning
Using high temperatures to kill microorganisms in food is one of the principal processes implemented on the preservation of food. The canning industry uses this method most extensively.

Acidity greatly reduces the time and temperature necessary to preserve foods by heat, even though that may contain resistant spores. High acid food such as grapes, pineapples, oranges and tomatoes, for examples, require only a few minutes at 100 degree C to preserve them; foods with acidity, such as spinach, corn, carrots, and beans, require much longer periods at high temperature – depending on the solidity, size of the packages and the amount of preheating.

There are three primary thermal processing methods used today; the conventional retort, the hot-fill and the high temperature short time methods (HTST).

The conventional retort method includes filling the can with the food product, heating the can sufficiently to kill microorganisms, sealing and slowly cooling the can. Whether the slow cooling period damages the food, whether the food is overcooked, and the type of food to be preserved must all be considered when this method is chosen.

The hot fill method is used primarily for high acid foods. Then a comparatively low temperature is sufficient to reduce the microbial; population to an insignificant level due to the pH level of these foods. The food is simply heated near boiling in a method similar to pasteurization poured into a sterile can while hot, and sealed.

Another commonly used method in the heat processing of food is the HTST method. Here the food is poured into the can and exposed to a high temperature for a comparatively brief time. Sealing is accomplished at the maximum temperatures, followed by rapid cooling. This rapid cooling, usually by immersion in cold water, prevents physical damage and over cooking of the product. One major problem with this process is that any microscopic leaks in the can allow the partial vacuum caused by the contraction of cooling to draw any microorganisms in the cooling water into the can.
Food Preservation by Canning