Michigan State University Extension
Preserving Food Safely - 01600936
10/13/97

### 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.

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