Food preservation uses more than one element in its process. Each method uses different elements to remove water and oxygen, and stop the growth of enzymes in the food to prevent the growth of microorganisms. Oxygen and enzymes allow microorganisms to flourish and multiply on fresh food, but when removed, the food stays preserved for as long as several years.
Drying
Drying, one of the oldest methods, only requires a source of heat to preserve the food. The heat, whether it's the sun, an oven or a dehydrator, removes the moisture from the food. Because the moisture content of the food is extremely low, the organisms that cause spoiling can't grow. When food is dried, it shrinks in size and takes up less space for storage, but drying does not retain the appearance or flavor of the food as well as other preservation methods.
Canning
In canning, foods are sealed tightly within a jar, keeping the liquid in, but the air out. When the air is completely removed, enzymes are destroyed, and this prevents the growth of harmful bacteria and mold. Foods are canned in either a pressure canner or water-bath canner. Low-acid foods -- with a pH higher than 4.6 -- such as meats, seafood and fresh vegetables, require a pressure canner to properly destroy botulinum spores. Acidic food such as fruits, pickles and jams have enough acidity to kill botulinum spores, so water canning is a sufficient preservation method.
Freezing
Freezing is a quicker preservation method than canning or drying and preserves the taste and appearance. Storing foods at cold temperatures prevents bacteria from growing, but freezer storage has other implications. Store food in containers that seal tightly to prevent air from penetrating the container; when food is not properly sealed in the freezer, ice crystals might develop around the food and affect the taste of the food. Vegetables require blanching -- a process in which the food is dipped into boiling water -- before you freeze them. The heat from blanching stops enzyme growth; if the enzymes are allowed to continue to grow during storage, the enzymes cause the vegetable to become tough or develop an unpleasant taste.
Lacto-Fermentation
Another method of preservation, not as widely used, is lacto-fermentation. The method involves combining fruits or vegetables with salt and whey and keeping the mixture at room temperature for a few days to produce lactic acid, a natural preservative that stops bacterial growth. Once the food is fermented, it is stored in a refrigerator or another cold storage area to keep the food fresh.
References
- University of Illinois Extension: Drying Food
- University of Nebraska Lincoln Extension; "Let's Preserve: Canning Basics"; Julie Albrecht; August 2010
- University of Wisconsin-Madison Food Safety: Preserve Summer Time's Best Flavors by Freezing Fresh Fruit
- Colorado State University Extension; "Freezing Vegetables"; P. Kendall; March 2008
- The Rosicrucian Fellowship: Lacto-Fermentation
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