Michigan State University Extension
Preserving Food Safely - 01600936
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.