How canning preserves foods

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The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their quality for several reasons: * growth of undesirable microorganisms- bacteria, molds, and yeasts, * activity of food enzymes, * reactions with oxygen, * moisture loss.

Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised, insect-damaged, and diseased food.

Oxygen and enzymes are present throughout fresh food tissues. Proper canning practices include:

* carefully selecting and washing fresh food, * peeling some fresh foods, * hot packing many foods, * adding acids (lemon juice or vinegar) to some foods, * using acceptable jars and self-sealing lids, * processing jars in a boiling-water or pressure canner for the correct period of time.

Collectively, these practices remove oxygen; destroy enzymes; prevent the growth of undesirable bacteria, yeasts, and molds; and help form a high vacuum in jars. Good vacuums form tight seals which keep liquid in and air and microorganisms out.

======================================================= === * USDA Agriculture Information Bulletin No. 539 (rev. 1994) * Meal-Master format courtesy of Karen Mintzias

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