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Canning -- Miscellaneous

What causes black deposit on the underside of canning jar lids after processing is completed?

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Black deposits on the underside of canning lids of properly processed products do not mean spoilage. Naturally occurring compounds in food react with the metal in the lid to produce the black deposit. This is especially common in tomato products. The products are safe to eat.

PREPARED BY: Angela M. Fraser, Ph.D., Associate Professor/Food Safety Specialist, and Carolyn J. Lackey, Ph.D., R.D., L.D.N., Professor/Food and Nutrition Specialist, North Carolina State University (August 2004)

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