How Does Canning Preserve Foods?

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.

Parts to a pressure canner

Boiling water bath canning is used for high acid foods such as tomatoes


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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.

*from uga.edu