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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