D: Little Miss Muffet, sat on her tuffet, eating her curds and whey. Alon--
Y: [in child's voice]: Wait a second there, pops! Eating her what?
D: [with uncertain authority]: Oh--uh, curds and whey.
Y: And what are those supposed to be?
D: Good question. Let's find out, on today's Moment of Science.
Actually, you've probably eaten curds and whey without knowing it, because curds and whey are the lumps and the liquid of cottage cheese. But what, exactly, are they? Well, cottage cheese is made from skim milk. So maybe the real question here is: how does skim milk become curds and whey?
In spite of its simple appearance, skim milk is chemically quite complex. There are dozens of different proteins floating around in that white fluid. Fortunately for cottage cheese makers though, all the proteins in milk can be separated into two basic groups, simply by adding a chemical called rennin. Rennin is an enzyme from a calf's stomach, and it makes some of the proteins in milk clump together. These clumping proteins are called "curd proteins," while the milk proteins that refuse to clump are called "whey proteins." These proteins are the curds and whey of Miss Muffet's lunch.
Unfortunately, whey doesn't actually taste very good--so modern cottage cheese makers tend to press or wash their product, leaving a cottage cheese that is mostly curds. But that's how you get curds and whey, little Angela. They are two kinds of milk proteins, which separate when you add rennin to them.
Does that answer your question?
Y: Sure, pops! But, hey! How do you sit on a tuffet?