Michigan State University Extension
Preserving Food Safely - 01600681


     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.                                               

Go To Top of File        MSU Extension Home Page        Main Page for this Data Base

This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned. This information becomes public property upon publication and may be printed verbatim with credit to MSU Extension. Reprinting cannot be used to endorse or advertise a commercial product or company. This file was generated from data base 01 on 03/09/98. Data base 01 was last revised on 10/13/97. For more information about this data base or its contents please contact wrublec@msue.msu.edu . Please read our disclaimer for important information about using our site.