This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
Occasionally even the most careful home canner has jars which become
unsealed during storage resulting in food spoilage. Exposure to high
temperatures or water during storage may cause the seals to break open or
the lids to rust through allowing microorganisms access to the food inside.
Any time a jar of home-canned food looks suspicious, treat it as though it
were spoiled. Low-acid home-canned foods such as vegetables, meat, poultry
and seafood are a special problem because of their association with botulism,
so spoiled in these food categories should be detoxified before they are
1. Do not taste food from an unsealed jar or any food which appears to be
spoiled. Presence of black discoloration, gas, swelling of the lid,
unnatural odors, spurting liquid and mold growth (blue, white, black or
green) indicate spoilage.
2. Spoiled, low-acid foods (including tomatoes) may have no evidence of
spoilage, so if they are suspect:
A. Swollen but still sealed jars can be put in the garbage (in
a heavy bag) or buried.
B. Unsealed jars should be detoxified.
A. Place containers and lids on their sides in a large pot (8 qt
B. Wash hands well.
C. Cover containers with water to at least 2" over them.
D. Put lid on pot and bring to a boil.
E. Boil 30 minutes.
F. Cool and discard (in trash bag or bury).
G. Scrub all counters, containers, equipment (including the can
opener), clothing and hands that may have had contact with
the food. Throw away sponges, wash cloths, etc. used in the