By Jayden Khuu '21
It’s not surprising to find that the “invention” of cheese came by accidentally some ten thousand years ago, a while before they first found a need to from civilizations, let alone the delicate art and chemistry of cheese-making. Legend says that an Arab nomad ten millennia ago had filled a saddlebag with milk on his journey across the desert by horse. The moment that continues to define our culinary experience now came when he wanted to quench his thirst a few hours later, only to find that the milk had separated into a pale watery liquid and solid white lumps, which he found the savoriness to be particularly enjoyable. What he did not know was that he performed the chemical reaction of coagulation.
What happened in that little saddlebag of his? Since the saddle bag was from the stomach of a young animal, the unpasteurized milk actually reacted with with rennet, which is produced in the stomach of ruminant animals. Let’s look further into the specific components that allowed for this reaction to happen. Unpasteurized milk naturally contains bacteria, which would increase exponentially in number over time due to its nature and would only speed up in desert temperatures. Then, we have Rennet, which is a complex set of enzymes that contains chymosin, an enzyme that speeds up the coagulation of milk. The coagulation of milk is a process in which the casein in milk is forced to change its structure due to the conditions in is put in.
The first condition is a high acidity; the high acidity destabilizes a certain protein subunit that is essential to keeping the structure of casein and keeping them dispersed throughout the mixture of milk. In the absence of these subunits, the casein clots together and forms a gel-like substance, or what we call a curd.
The second condition is the presence of chymosin. Chymosin, plays a similar role by inactivating the kappa casein molecule, one of the four in casein, who contributes to making milk protein soluble and prevents it from spontaneously coagulating.
Milk coagulation would happen already if the first condition is met, but the process would be much quicker if we add Rennet for the chymosin to enhance the reaction . In the case of our Arab Nomad, both happened at the same time that led to such a quick coagulation of milk into cheese.
There are seven categories of cheese nowadays and there are more than a few thousand cheeses within each category. The characteristics of the cheese that allows for us the luxury of distinguish them depends heavily on how the cheese is coagulated. For an example, Queso Fresco, a soft and creamy cheese that is often found in Quesadillas, is made through acidic coagulation, by simply adding vinegar in the process. On the other hand, the cheddar we all love, is made by adding rennet and small amounts of the bacteria meso I to milk, and over time allow the bacteria to grow and slowly induce the coagulation process, allowing for the strong flavor and hard texture. We only see an entire assortment of cheeses that come from a variety of countries in the cheese section of a supermarket, we should now also see how all these cheeses comes from the intricate balance of one chemical reaction.
Sources:
http://www.gol27.com/HistoryCheese.html
https://www.thecheeseweb.com/7-types-of-cheese
https://www.uoguelph.ca/foodscience/book-page/milk-coagulation
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