The origin of cheese is assumed to predate any recorded history of cheese itself. The proposed date of origin ranges from 8000 BCE to 3000 BCE. At this time, many people used dried animal stomachs to store a variety of substances, such as milk. The creation of cheese was most likely an accident (a very good accident that is.) Most likely a herdsmen stored milk in one of these stomach “containers,” and when the milk was left out in the sun in the container, a chemical reaction took place. The heat caused the milk to combine with rennet, the digestive enzyme that lines the animal’s stomach, causing the milk to coagulate and create a white lump form known as curd in a water-like whey fluid.
Whey contains a 5% mixture of lactose in water as well as the dissolved aspects of the original milk. The whey and curd are separated after they are fully formed using a cheesecloth and other techniques, and the whey can then be used for other purposes such as making processed cheese. The protein matrix that remains in the curd becomes more compacted as the whey is removed. The cheese curd that is created holds much of the milks original nutritional value including the protein source of casein. The rennet forces the casein to separate from the milk and to become part of the curd. In itself, casein holds carbon, nitrogen, oxygen, hydrogen, phosphorus, and sulfur. Rennet is one of the most important factors of the chemical process of cheese creation.
“Rennet (chymosin) is a proteolytic enzyme and its role is to destabilize casein micelles and make them to coagulate. Similar enzymes are also found in plants, microorganisms, and digestive tract tissues of other animals including chickens. They break down k-casein present on the surfaces of casein micelles in milk. Deprived of the protective action of k-casein, casein micelles form a gel. When examined by electron microscopy, they form a thin matrix consisting of their clusters and short chains, encapsulating fat globules. Void spaces in the matrix are filled with the liquid milk serum called whey which is a solution of lactose, minerals, and vitamins, and a suspension of whey proteins. The subsequent steps in the cheese manufacture are aimed at separating the curd from the whey and ripening it.” (source)
In modern production (thankfully no animal stomachs are directly involved), the milk is soured and then rennet is added in order for the curds and whey to form. Every cheese has its own unique process of curdling and production. While some cheeses require the addition of acidity in order to curdle, others are just treated with rennet. The softer and fresher the cheese, the more acid is involved, while the more aged and harder forms are mainly curdled with rennet.
When the curd and whey is completely separated and the curds are combined together to form the cheese substance, a soft and almost gel-like substance is formed. After being drained, salted, and cased in wrapping, this substance is ready to be eaten. However, in order to create a firmer and tastier cheese, this gel like substance needs to be aged. During the aging process, known as affinage, microbes and enzymes cause the flavor of the cheese to become bolder and the texture to change. As the casein proteins and milk fat breakdown into amino acids, fatty acids, and amines, the cheese begins to change. Often times, additional microbes, or better known as bacteria and molds, are released into the environment of the aging facility or are put directly into the cheese in order to additionally affect it in the aging process. Bacteria and mold can also be added to cheese to adjust its flavor or pH level. From the type of animal milk to the length of aging to the amount of milk fat and even the treatment processes, creating a cheese is not always an easy feat.
So as of now we know the basics to the chemistry of cheese. Check back next week for even more about the science of fromage.
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