This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
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. Hhowever, 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
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
5. White crystals on tomato products: home-canned pureed tomato products
may have crystals of calcium nitrate on the surface. They are hard and
scaly 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 45F 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
12. Colorless crystals which look like broken glass in canned sea foods.
Prepared by Susan Brewer/Foods and Nutrition Specialist/Revised, 1992