COLOR CHANGES IN HOME-CANNED FOODS

   

   The pigments in food which are responsible for their colors
are sensitive to a variety of things which they may come into
contact with during home food preservation.  Acids (lemon or
other fruit juices), anti-caking ingredients in table salt,
minerals in water, metals in water and from cooking utensils,
heat, and light are a few things which can affect these pigments
causing them to change color.  Most color changes which occur
during home food preservation do not make the food unsafe to
consume--however, if the food looks or smells bad or odd, do not
take a chance, dispose of it without tasting it.

   1.     Blue garlic: Occurs in pickled products.  Caused by
          using immature garlic or because table salt was used in
          place of canning salt.  Not a safety hazard.

   2.     Yellow cauliflower:  Cauliflower (or other white
          vegetable pigments) are white in acid but yellow in    
          alkaline medium.  Minerals in the water may have
          created a more-than-normal alkalinity.  Not a safety
          hazard.

   3.     Yellow crystals in canned asparagus: the crystals are
          glucosides (rutin) which were in the asparagus cells
          before canning.  The high temperature of pressure
          canning causes them to come out of the vegetables into
          solution, but when the food cools, the pigment
          precipitates out of solution onto the the asparagus.  
          Occurs mainly in asparagus in glass jars.  If asparagus
          is canned in tin cans, a pigment-tin complex form so
          the yellow pigment stays in the liquid.  Not a safety
          hazard.

   4.     Pink pears: the light colored pigments in the pears
          convert to pink pigments due to overprocessing or due
          to enzymatic reactions.  Not a safety hazard.

   5.     White crystals on tomato products:  home-canned purred
          tomato products may have crystals of calcium nitrate on
          the surface. They are hard and scaley unlike mold
          spots.  Not a safety hazard.

   6.     White crystals on spinach leaves: calcium oxalate--not
          a safety hazard.

   7.     White or pink crystals in grape jelly:  Grapes are high
          in tartaric acid which goes into solution during
          cooking but precipitates as crystals during cooling. 
          Prevent crystals by extracting grape juice, cooling
          overnight in the refrigerator and filtering juice
          before canning or using for jelly-making.  Not a safety
          hazard.

   8.     White, yellow, or pale red beets: the red pigments in
          beets (anthocyanins) are sensitive to high
          temperatures.  Some beet varieties are especially     
          sensitive.  The pigments are converted to white or
          colorless derivatives.  Not a safety hazard.

   9.     Blue pickled  beets: the pigments in beets are
          pH-sensitive.  They are red in acids and blue in
          alkalis.  If the pigments are blue, the pH is too       
          high for water-bath canning to be safe.  Throw the
          beets away (handle according to spoiled food
          procedures).
   
   10.    Brown green beans: enzymatic color changes occurring
          before the enzymes are inactivated by heat cause the
          green-to-brown color change of chlorophyll.  Blanching
          or hot-packing will inactivate the enzymes and help
          preserve the green color.  Not a safety hazard.

   11.    Brown potatoes:  storage of potatoes at temperatures
          below 45 F causes the potato starch to be converted to
          sugars.  During high heat treatment of pressure
          canning, these sugars form dark brown pigments.  Not a
          safety hazard.             

   12.    Colorless crystals which look like broken glass in
          canned sea foods.  Not harmful.

Prepared by Susan Brewer
Foods and Nutrition Specialist
Revised, 1992                                          EHE-666