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
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 http://extension.missouri.edu 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
Last update: Tuesday, December 09, 2008