On Food and Cooking

protein coagulation.
When milk itself is a prominent ingredient
— in cream soups, sauces, and scalloped
potatoes, or added to hot chocolate, coffee,
and tea — it most often calls attention to
itself when its proteins coagulate. The skin
that forms on the surface of scalded milk,
soups, and sauces is a complex of casein,
calcium, whey proteins, and trapped fat
globules, and results from evaporation of
water at the surface and the progressive
concentration of proteins there. Skin
formation can be minimized by covering the
pan or whipping up some foam, both of which
minimize evaporation. Meanwhile, at the
bottom of the pan, the high, dehydrating
temperature transmitted from the burner
causes a similar concentration of proteins,
which stick to the metal and eventually
scorch. Wetting the pan with water before
adding milk will reduce protein adhesion to
the metal; a heavy, evenly conducting pan and