Because butter contains milk solids
(actually proteins), which burn at relatively low temperatures, it can't
be used to sauté at the high temperatures required for browning most meats
and seafood and some vegetables. Whole butter also contains water - about
25 percent - that can make certain sauces, such as hollandaise, too thin.
To solve both problems, professional cooks often clarify butter, removing
the water and milk solids.
Butter can be clarified using one of
two methods. The first, used in professional kitchens where large
amounts of butter are clarified, consist of melting the butter in a large
pot and letting it sit for about half an hour, during which time the water
sinks to the bottom and the milk solids float to the top. The milk solids
are skimmed off with a ladle and the clarified butter - which is now pure
butterfat - is ladled off and saved. This is impractical in home kitchens
because it's hard to do with a small amount of butter.
To make a small amount of clarified
butter, put two or three sticks of butter in a small heavy-bottomed
saucepan. Cook the butter over medium heat for about ten minutes, until
the water boils out of the butter and the milk solids turn pale brown,
then strain out the milk solids. Not only is butter cooked in this way
clarified, but its flavor is enhanced by the caramelized milk solids.
Indian cooks call butter clarified this way - Ghee.