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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