I was getting a salad at the cafeteria on campus the other day and there were four cheese options—so I chose all of them. The thought then occurred to me, “what even is cheese, and why are they all so different?” Thus began a delightful search into the molecules that make up cheese.
The major component of cheese is a protein called casein. In fact, both the names cheese and casein come from the Latin caseus meaning cheese, which should give you a sense of how ancient the art of cheese making actually is. Casein, a protein found in milk, is not soluble in water. Instead, casein attracts calcium ions to form globular structures that disperse themselves in the water. This is called an emulsion, but that’s why leaving milk in the freezer results in two different layers—one water layer and one with all the water-insoluble molecules. In order to form cheese, the casein proteins have to coagulate.
There are two ways of doing this: acidity and rennet. Acidity is the easiest way to get the casein to group together. In some cheeses like paneer, this is done with the addition of actual acids like vinegar or lemon juice. But this results in a very weak, soft curd. So instead, the cheese maker will add a bacteria like Lactococcus or Lactobacillus that converts milk sugars into lactic acid. This works well for many soft cheeses, but something more is needed to get the right texture.
For harder cheeses, a cheesemaker will use rennet. Rennet is a complex mixture of enzymes produced by infant cattle that helps them break down milk. The main enzyme is called chymosin and is now made primarily in the lab through genetic engineering. Chymosin breaks apart casein into hydrophobic (water-hating) and hydrophilic (water-liking) segments. The hydrophobic segments then form an extended network that gives cheese curds their rubbery texture.
With curds in hand, the next steps to making cheese involve removing water and adding flavor. For soft cheeses, the water is often just drained off and the cheese is packaged and ready to go. But for harder cheeses, further processing is required. In some cases, this involves heating the curds in an oven to evaporate off more water. In the case of cheddar cheeses, the curds are repeatedly piled on top of each other and pressed. The addition of salt also helps to draw out water.
But the real magic of cheese comes from the microbiome that grows within it. Most of the flavors associated with cheese come from bacteria that feed on the sugars, fats, and proteins in the curds to produce small molecules that are responsible for distinct flavors. These molecules and the bacteria that make them will be the focus of a later article in which I hope to interview a special expert. For now, I hope that you have at least developed more of an appreciation for the importance of protein networks in cheese texture.