What is the foam that comes out when making clarified butter?

Question

When making clarified butter you get a bottom layer of milk solids, the center layer of clarified butter, and the top layer of foam. What is in the foam? Does it have any uses?

Answer 1

That foam is more of the milk solids, brought up and made foamy by water evaporating. The Joy of Baking says it is whey protein specifically.

I usually discard it but you can eat it. Some people like it on toast or other places where you might use butter or a light sprinkling of mild cheese.