Rennet: The bovine enzyme cheese-eaters eat every day

Thousands of years ago, shepherds and farmers made a mistake. In order to transport their drinking milk, people stored it in sacks made from the stomachs of sheep. After being stored for some time, it was found that the resulting concoction was no longer milk, but had instead separated into solids and liquid, or curds and whey. It was with this mistake that the use of animal rennet in cheese production entered the collective stream of consciousness, and grew to become the practice still routinely used today.

“Rennet, or rennin, contains protein-digesting enzymes, [or] chemical catalysts that speed up metabolic reactions,” says Santa Monica College biology professor Thomas Chen in an e-mail.

All infantile mammals are born with this enzyme, as it is most effective as a milk coagulant, and allows animals to properly digest their mother's milk.

“[Rennet] is found throughout life’s major domains and kingdoms, from bacteria to mammals, because all living things must be able to digest proteins,” says Chen.

In traditional cheese production, farmers extract rennet from the stomachs of calves and lambs, and use the enzyme to coagulate milk from which various cheeses can be made.

Though this process may sound slightly barbaric, young mammals are reportedly not slaughtered solely for this purpose.

Animal rennet is used in most cheeses, but for strict vegetarians opposed to its consumption, certain cheeses contain non-animal sources of rennet.

Thistle, for example, is a popular source of rennet that is frequently used in the production of Mediterranean cheeses. When the enzyme is derived from a plant like thistle, the resulting taste of the cheese is often very light and floral.

Employees at Andrew's Cheese Shop in Santa Monica say that while a select few of their cheeses are made with plant-based rennet, the majority of their products contain animal rennet because, “it makes a better product.”

Andrew's products are boutique European and American cheeses, and are often made from very low-production farms.

“We know the cows and sheep that produce the milk for our cheese,” says Colleen, an Andrew’s Cheese Shop employee who declined to provide her last name. “We know the cheese-makers, and they never slaughter animals specifically to extract rennet for the cheese. It's always a byproduct.”

Despite the regular use of animal rennet in gourmet cheeses, in recent years, the world has taken a turn toward genetically engineered rennet, as the process is often far less expensive and time-consuming than extracting the enzyme from plants and animals.

According to an article from the European Commission of Health and Consumer Protection, the production of genetically engineered rennet began over 100 years ago.

“In 1874, a Danish chemist, Christian Hansen, founded a laboratory in Copenhagen and commenced the first commercial production of rennet from calf and adult cattle stomach,” according to the article.

As time passed and the process was perfected, more cheese producers began to use artificially-created rennet.

Though it may be slightly unnerving to realize that the production of cheese relies on an enzyme traditionally found in bovine and lamb stomachs, there are alternatives available for the discerning eater.

Vegetable and plant-based cheeses like Humboldt Fog, La Serena and Brazo's Select are entirely vegetarian, and often use raw milk as opposed to that which has been altered for cheese production.