What is The Foam while making jam?

I was teaching a friend how to make jam today. She asked about the foam. The Foam you say. Yes the foam. 

I can remember when I was little my grandma use to scrape the foam from the top of the jam and put it in a bowl then spread it on Hot Biscuits for us. It was the best part of the jam.

But in reality the foam is just the result of bubbles from the boiling jam coming up through the viscous jam. 

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. 

You get the most foam from making strawberry jam.  The riper the strawberry the more foam and float.

Strawberries have air in them and the foam is a result of the boiling process releasing the air and forming bubbles or foam

They do tell us to skim the foam. Another way to stop it is add a teaspoon of butter.
Who wants butter in there jam prior to making the toast.
 
Did you know that strawberries have air in them and the foam is a result of the boiling process releasing the air and forming bubbles or foam.

Disclaimer: This is not an all inclusive recipe for making jam. You should have a basic knowledge and understanding of the canning process before proceeding. Please consult your local Center for Home Preservation for additional information and available classes.