Chemistry of Cheese Making

Last week, we learned about the molecular components of milk and the chemistry behind cheese making. Milk is made of three simple components: proteins (casein proteins and whey proteins), milk fat, and lactose (a complex sugar combination of glucose and galactose). Cheese is made by curdling milk using an acid, heat and an enzyme called rennet to alter the molecular structure of the casein proteins. In our experiment, each group heated half a gallon of milk in a pot on a hot plate. We added 1/8 of a teaspoon of vegetable rennet and ¾ of a teaspoon of citric acid and could right away see the formation of curds. After letting the milk rest covered for 25 minutes the curds had separated even more from the whey. Why does this happen? Micelles of casein proteins consist of many individual protein molecules with negative charged ends held together by particles of calcium phosphate. Normally these negative charged ends help keep the micelles far apart from one another. The rennet enzyme we add essentially “clips” the ends of these protein molecules, causing the micelles begin to clump together. We further separated the curds from the whey by straining the mixture through cheesecloth and heating the remaining curds in the microwave. I was surprised at how much more whey there was compared to our finished mozzarella cheese product.