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Canning -- Miscellaneous
What causes a lid to become corroded or rusted while it is on a jar of home canned food?
Following the manufacturer?s instructions for preparing and using lids will reduce the possibility of corrosion. It is also important to use home canning lids that have been stored in a cool, dry, dark place. If corrosion does occur, one of the following factors may have been the cause: not preparing lids for use according to manufacturer?s instructions; scratch in the enamel surface of lid; incorrect headspace; strong concentrations of salt or acid; improper storage of lids prior to canning; not removing bands before storing sealed jars; not wiping off lid and jar surface with a clean damp cloth to remove food particles and residue. A jar of home canned food with a lid that becomes spotted with rust may be used as long as it was properly processed using up-to-date methods (see Canning Basics), and there is a vacuum seal on the jar. Please note this applies to surface spots only. Source: Original FAQ posted at http://www.homecanning.com/usa/alfaq.asp