Michigan State University Extension
Preserving Food Safely - 01600681
08/03/99
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.
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 05/29/03.
Data base 01 was last revised on 08/03/99.
For more information about this data base or its contents please contact
wrublec@msue.msu.edu . Please read our
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