Frequently Asked Questions
Search Knowlege Base
Canning -- Miscellaneous
Why do the undersides of metal lids sometimes discolor?
Natural compounds in some foods, particularly acids, corrode metal and make a dark deposit on the underside of jar lids. This deposit on lids of sealed, properly processed canned foods is harmless. Source: Original FAQ posted at http://184.108.40.206/faq/FAQ_home.php