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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