Pfizer’s Genetically Engineered Chymosin Dominates US Cheese Production

In the 1980s Pfizer created a chymosin enzyme by inserting the gene for bovine chymosin into a genetically engineered strain of Escherichia coli. The resulting fermentation‑produced chymosin (FPC) was approved by the U.S. Food and Drug Administration in 1990 as generally recognized as safe.

The enzyme performs the same function as traditional calf‑derived rennet—cutting kappa‑casein to coagulate milk—while offering greater consistency, scalability and lower cost. Thirty years later, industry estimates suggest that 90 % to 95 % of American cheese is made with this genetically engineered enzyme, effectively replacing the conventional animal source.

The widespread adoption has reshaped the U.S. cheese supply chain, prompting discussions about possible links to rising dairy sensitivities and broader public‑health trends in the United States.