Why put butter in Jam and Jelly?

The following question was ask as a comment on one of my jelly recipes.  I thought it deserved a spot under Q&A so that if there are any other canners wondering the same thing, you would have an answer. 

Q: 

Catina HoakJune 22, 2013 at 6:17 AM

what purpose does the butter have in the recipe ? have you tried leaving it out ? Butter can turn rancid and I know it is a small amount but I would double/triple the batch for gifts.
TinaH

 

A: 

Butter helps reduce foaming when making jam or jelly. It is an optional ingredient and if you check the tips in your boxes of Ball Pectin and the Ball Blue Book you will find that it also tells you to use a little butter to reduce foaming.  I have never had a problem with any of my jams or jellies by using it.