Title: How Canning Preserves Foods
Categories: Canning, Information
Yield: 1 guide

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.

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* USDA Agriculture Information Bulletin No. 539 (rev. 1994)

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