Had a few good questions come in over the long weekend about clarified butter. Reader Ken asked if the “proteins” I mentioned in the baklava post are the same thing as “milk solids” and if so, what sorts of proteins they are. These are the sorts of questions I live for.
“Milk solids” are indeed another name for the proteins found in milk. There are literally scores of different kinds, though they can be grouped into two general categories: caseins and whey proteins. Caseins are the proteins that clump up in the cheese-making process to form curds. Whey proteins are, well…whey.
Being made from milk, butter retains some of these proteins. In fact casein and whey proteins make up about 5% of butter’s total mass. Heat butter and the proteins start to separate out, though in different ways. The whey proteins rise to the top along with the water (which quickly evaporates off) forming a frothy layer, while the caseins clump up and sink. What’s left in the middle is what’s known as “clarified butter” or “ghee”.
“Clarifying” butter simply means skimming the whey foam off the top, which you can do with a spoon. As for the caseins, they can be left where they are. Just dip your brush carefully so as not to churn them up while you’re buttering your pastry.