Most cheese is made of basically the same thing: Milk, microbial cultures, and rennet.
Rennet is an enzyme that helps the milk proteins coagulate, binding together into what will become the curds. Traditionally it comes from calf's stomachs, but since the 1960s, it's been more common to get rennet from a cloned microorganism.
To start the cheese-making process, you take some (usually) pasteurized milk and add a starter culture to it. Those microbes snack on the lactose in the milk, beginning the fermentation process. Then you add in the rennet. When the curds form, what's left over is a liquid called whey. The curds are then heated and cut up.
In the end, you get a bunch of curds that get packed together and aged into cheese, Tunick said.