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How Canning Preserves Foods


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How Canning Preserves 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.

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.




General Information

  • General Information - Jams & Jelly Products
  • Types of Jellied Products
  • Jellied Product Ingredients


  • Extracting Juice for Jelly
  • General Information on Canning Jams, Jellies, and Marmalades
  • Making Jelly without added Pectin
  • Making Jam without added Pectin
  • Making Jams and Jellies with added Pectin
  • Processing Jams and Jellies
  • Steps in Processing Jams and Jellies
  • Testing Jelly without Added Pectin
  • Remaking Soft Jellies
  • Stiff Jams or Jellies
  • Storing Home-Canned Jams and Jellies
  • Causes and Possible Solutions for Problems with Jellied Fruit Products
  • These documents were adapted from the "Complete Guide to Home Canning," Agriculture Information Bulletin No. 539, USDA, revised 2009 &
    From "So Easy to Preserve", 5th ed. 2006. Bulletin 989, Cooperative Extension Service, The University of Georgia, Athens. Revised by Elizabeth L. Andress. Ph.D. and Judy A. Harrison, Ph.D., Extension Foods Specialists.