Calories in Cheese

What makes cheese so powerful?

The transformation of liquid milk into solid cheese relies on a fascinating biological hijacking. When rennet—an enzyme complex traditionally extracted from the stomach lining of calves—is added to milk, it targets casein, the primary milk protein. Casein exists in milk as spherical micelles, held together by calcium phosphate and a surface layer of kappa-casein. Rennet's active enzyme, chymosin, acts like molecular scissors, snipping off the kappa-casein hairs. Without this protective layer, the micelles lose their negative charge and repulsion, causing them to rapidly clump together into a solid curd. This curd traps milk fat and expels the watery liquid known as whey, which contains most of the lactose and water-soluble proteins. The curds are then pressed, salted, and left to age. During aging, surviving bacteria and enzymes continue breaking down proteins and fats into flavor compounds like amino acids and fatty acids. This slow autolysis is why an aged cheddar tastes sharp and complex, while a young mozzarella remains mild and elastic. The entire process turns a highly perishable liquid into a shelf-stable food.