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Why skim the foam off the jam?


Skimming the foam off is part of the recommended safe procedure for canning jam. But why?!

Clearly foam on the top of a nice jar of jam affects its appearance. But in fact there is a little more to it. Foam contains a lot of air. In canning, the jars are not filled to the top of the jar. This gap between the lid and the food is called head space and it gives the canned food room to “breathe.” The food can expand during processing and form a vacuum as the jar cools. Foam in a jar of jam increases the head space. According to the Food Safety Information Service, this is not a problem if the jam is stored in a cool place and is eaten relatively soon. The extra head space does increase the chance of the jam molding after prolonged storage though.

There is usually a very reasonable explanation for the steps we follow in cooking. For more information and the exact steps to follow to safely can vegetables and fruits, to make jellies and jams, or to pickle your produce, ask for the Quality for Keeps series of guide sheets from your local University of Missouri Extension center. Or log onto the web at and click on Publications and then Extension Guide Sheets or use the search box on the home page. And then enjoy canning and knowing the safe procedure to preserve your harvest.


Janet Hackert, Nutrition Specialist, Northwest Region, University of Missouri Extension






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Last update: Tuesday, December 09, 2008



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