Michigan State University Extension
Preserving Food Safely - 01600681
10/13/97

JAR LIDS-BLACK SPOTS

     Black  spots on the underside of the lid does not  mean
the food is spoiled.  Naturally occurring compounds in foods
including tannins, hydrogen sulfide or nitrogenous compounds
can  react  with  metal lids  causing  black  spots.   These
reactive compounds are associated with proteins in the food.
When  subjected   to  heat  of processing, proteins denuture
and these  compounds are  released.   Once  freed  from  the
protein, they are able to combine with the metal lid causing
brown or black deposits.                                    

     If the jar of food is no longer   sealed (vacuum lost),
black spots on the underside of  the lid  mean that the food
is  spoiled.   In this case, the contents of the  jar should
be discarded.                                               

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