I found brown and black deposits on the underside of the canning lid when I opened a jar of home canned food. Is the food safe to eat?
Brown or black deposits on the under side of metal lids are harmless. The underside of metal lids is protected by an enamel coating. If there are any imperfections in the enamel (for example, tiny scratches or pinholes) natural compounds in food can react with the metal in the lid to form brown or black deposits. The food may be eaten as long as there are no signs of spoilage evident.
Caution: If there are holes through the lid,
the food must be discarded so that it cannot be eaten by
humans or animals.
Barbara Willenberg, Nutritional Sciences, University of Missouri-Columbia
Last update: Tuesday, May 05, 2009