Mammals whose milk is used for cheesemaking, such as cows, goats, sheep, and water buffalo are known as ruminants. Ruminants are mammals who obtain their nutrients through digestion of plant matter and are further classified by their four chambered stomachs, each chamber performing a specific function in the digestion process. Two of these chambers are essential in the production of milk that is directly related to the cheesemaking process: the rumen and the abomasum.
In the rumen, the feed ingested by the ruminant is fermented within the microbiome of the chamber. As the feed is quickly ingested by the animal it is brought through a dual path esophagus to the rumen where it goes through a fermentation process. Once the digestion has begun, the fermentation produces gas which is released from the rumen through burping, as this happens the partially digested feed is regurgitated up the esophagus to the animals mouth where the animal the chews it into a "cud." This "cud" is chewed again by the animal, producing saliva that contains a natural antacid, which then buffers the acidity of the rumen. This balancing allows the animal to get the most from their feed, which eventually leads to a more nutrient and microbial dense milk and of course cheese.
We recently attended a talk led by Dr. Itzhak Mizrahi at MIT on the microbiome of the rumen in cows. During his presentation, Dr. Mizrahi touched on feed efficiency and optimizing quality of certain cows through breeding and genetics. His research has found that more efficient cows absorb more of the nutrients and microbes in the feed, thus producing less waste and leading to a higher quality of milk. By determining which types of feed are most efficiently digested, as well as breeding the most efficient cows, dairy farmers can optimize their herd to yield the highest quality and volume of milk.
Another key part of cheesemaking comes from the fourth chamber of the ruminant's stomach, the abomasum. It is the abomasum that the enzyme, chymosin, is found. The natural function of this enzyme is to clot milk in the stomach of young ruminants, making digestion easier as the four chambers of the stomach are not all functioning in younger ruminants. These enzymes are isolated from the abomasum of young ruminants and used as rennet in cheesemaking. This process mimics the natural process that occurs in the abomasum of young ruminants by coagulating milk and separating the curds which will be used for cheesemaking!
Daniel McElligott, Oldways Cheese Coalition Research Consultant
Image from: https://www.extension.umn.edu/agriculture/dairy/feed-and-nutrition/feeding-the-dairy-herd/ruminant-anatomy-and-physiology.html