Traditionally, cheese production relied on milk, salt, starter cultures (bacteria to ferment the milk), and animal rennet, an enzyme complex from the stomachs of young ruminants like calves, to coagulate milk into curds. However, modern industrial cheesemaking has shifted significantly.
Fermentation-Produced Chymosin (FPC), a genetically engineered enzyme, was developed by Pfizer in the 1980s and approved by the FDA in 1990 as the first bioengineered food ingredient.
90 % of USA cheese is fake!Traditionally, cheese is made with just four ingredients, milk,salt,starter culture & an animal rennet.
— Humanbydesign (@Humanbydesign3) February 25, 2025
But in today’s industrial food supply, 90% of cheeses contains something called FPC, a genetically modified version of animal rennet made by #Pfizer. pic.twitter.com/GCBjbSbWRS
FPC is produced by inserting the animal-derived chymosin gene into microorganisms like bacteria or yeast, which then synthesize the enzyme. Industry estimates, including from the American Cheese Society, suggest that around 90% of cheese in North America uses FPC due to its cost-effectiveness, consistency, and appeal to vegetarian markets (as it avoids animal slaughter).
While Pfizer pioneered FPC, other companies now produce it too. Labeling loopholes mean FPC is often listed as “microbial rennet” or “vegetable rennet,” not GMO, despite its bioengineered origins, leaving consumers unaware of its presence.
It’s estimated that around 90% of cheeses produced in the United States contain FPC, a figure that comes from industry insights, including statements from experts like those at the American Cheese Society and cheesemaking professionals.
The shift began in the 1990s, and today, most mass-produced cheeses—like cheddar, mozzarella, and processed varieties—rely on FPC. Artisan cheesemakers may still use animal rennet, but they represent a small fraction of the market. Exact statistics can vary slightly depending on the source, but the 90% estimate aligns with widely accepted industry trends in the U.S. cheesemaking landscape as of early 2025.
U.S. labeling laws don’t require FPC to be identified as a GMO ingredient. The FDA considers FPC “Generally Recognized as Safe” (GRAS) and classifies it as equivalent to traditional rennet since the end product—chymosin—is chemically identical to its animal-derived counterpart. Plus, the microorganisms are removed after production, so the final cheese doesn’t contain GMOs, just their byproduct.
As a result, FPC is often listed vaguely on labels as “microbial rennet,” “vegetable rennet,” or simply “enzymes,” dodging any GMO connotation.
Critics argue this exploits a loophole, obscuring transparency, while supporters say it avoids unnecessary consumer alarm over a safe, widely used ingredient. Either way, most Americans eating cheese with FPC don’t know its bioengineered roots.