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Historically, chymosin was extracted from young cow stomachs, but in the 1990s scientists managed to genetically engineer a bacterium to synthesize it.

The protein chymosin, produced in the stomach, turned liquid milk into a semisolid form.

Human young don’t produce chymosin, using different enzymes to attack milk proteins, but that doesn’t mean that we don’t find it useful.

Hard cheeses require the use of chymosin, an enzyme found naturally in the stomachs of ruminant animals.

But an estimated 90 percent of American cheese, for example, is made with cultured chymosin, a vegan rennet replacement made using genetically engineered Aspergillus fungi.