Foaming Soup

Ask the Test Kitchen

I enjoy preparing split pea soup, but I’ve noticed that when the water comes to a boil, a foam forms over the water surface. I skim the foam off, but why does that happen? —L.B., Brevard, North CarolinaAccording to the U.S. Dried Pea and Lentil Council, dried peas, like rice, contain a lot of starch. At very hot temperatures, the starch reacts with the water molecules, causing an increase in surface tension, which ultimately forms small bubbles or pockets of air surrounded by the starch, creating foam.

To reduce the foaming, peas, beans, lentils, chickpeas and rice can be soaked for a short amount of time to remove some of the excess starch before cooking. For the most part, foaming cannot really be avoided.