Cheese is a staple in most American diets. Milk was coagulated with rennet taken from the stomach lining of an unweaned calf to produce cheese. The calf naturally produces chymosin to digest its mother’s milk, and cheesemakers learned centuries ago how to use that enzyme to separate milk into curds and whey. Then the laboratory entered the barn.
During the 1980s, Pfizer developed a chymosin preparation made through genetic engineering. Scientists took the genetic instructions associated with bovine chymosin and placed them into a microorganism. The altered organism could then be grown in industrial fermentation equipment and made to produce the desired enzyme in enormous quantities.
In 1990, the Food and Drug Administration affirmed Pfizer’s fermentation-derived chymosin preparation from genetically modified E. coli K-12 as generally recognized as safe. The FDA record identifies Pfizer Central Research as the petitioner and amended federal regulations covering animal-derived rennet and fermentation-derived chymosin. This was not some internet rumor. It is written directly into the government’s own regulatory history.
That approval marked a major turning point. One of humanity’s oldest foods could now be produced using an enzyme manufactured by a genetically engineered microorganism rather than obtained from the animal source nature provided.
The product is called fermentation-produced chymosin, or FPC. It performs the same basic task as calf chymosin by cutting a milk protein known as kappa-casein, destabilizing the milk and forming curds. The attraction to the industry was obvious. It offered consistency, scale, predictable strength, fewer supply constraints, and less dependence on slaughtered calves.
This was not introduced because consumers marched through the streets demanding genetically engineered cheese enzymes. It was introduced because industrial production wanted a cheaper and more controllable input.
That is how the modern food supply changes. Nobody holds a national referendum. The corporation submits its data. The regulator gives its approval. Manufacturers adopt the technology. Thirty years later, the consumer discovers that the traditional ingredient quietly disappeared from much of the mass market. Then the public questions why instances of dairy intolerance are on the rise, or why America has become the least healthy nation in the developed world.
Now, 90% or even 95% of American cheese uses genetically engineered rennet. Pfizer’s current production volume is not publicly disclosed, and today’s enzyme market includes other large biotechnology suppliers. Pfizer was an early commercial and regulatory pioneer. It helped establish the technology, but there is no evidence that it currently controls the American cheese supply. That does not make the story less disturbing.
The United States Department of Agriculture also acknowledges exactly what FPC is. USDA organic-review materials state that fermentation-produced chymosin is derived from genetically modified organisms and is not permitted in organic processing. A 2024 USDA document added another extraordinary fact: regulators currently lack the ability to determine the origin of an enzyme sample after it has been produced.
Think about what that means. The government can approve the production process, yet once the enzyme is isolated and purified, the regulator may not be capable of examining a sample and determining whether it came from a genetically altered microorganism. Traceability therefore depends heavily on company records, supply chains, certifications, and paperwork.
Federal law generally requires ingredients to be identified by their common or usual names. Yet food enzymes can also function as processing aids, and American cheese labels frequently use broad declarations such as “enzymes.” That does not tell the buyer whether the coagulant was traditional calf rennet, a fungal or bacterial coagulant, vegetable rennet, or fermentation-produced chymosin manufactured using genetically engineered microorganisms.
You could stand in the dairy aisle and read every package. Unless the manufacturer voluntarily provides greater detail, you may still have no idea which process was used. How can consumers reward traditional cheesemakers when the government permits the essential production method to disappear behind the word “enzymes”? Price, fat, and sodium are visible. Yet the origin of the substance that turned the milk into cheese may remain concealed.
Europe is not entirely free of fermentation-produced chymosin, although there are restrictions. It permits food enzymes made with genetically modified microorganisms after regulatory safety assessments. The European Food Safety Authority has evaluated chymosin produced by genetically modified yeast and fungal strains for use in cheese and fermented dairy products. The difference is that Europe has also preserved legally enforceable production standards for many traditional regional cheeses.
Put it on the label! State “animal rennet” when it comes from an animal. State “microbial coagulant” when it comes from a conventional microorganism. State “fermentation-produced chymosin made using genetically engineered microorganisms” when that is how it was produced. Let the public decide.
The FDA did not require special labeling when it approved Pfizer’s fermentation-produced chymosin in 1990. Even today, supporters point out that roughly 90% of American cheese is made using this process because it is cheaper, more consistent, and less dependent on calf rennet. The issue, however, has never been whether industrial production is more efficient. The real question is why consumers were never given meaningful transparency. If government and industry are so confident there is no practical difference, then simply tell people how their cheese was made and let the market decide. A free market depends on informed consumers, not information filtered through regulators and multinational corporations.