Cheese is one of the few foods that can start a family argument without anyone leaving the kitchen and lately, it has managed to do it without changing taste, price, or packaging.
The trigger is an ingredient most shoppers never see. In North America, roughly 90% of cheese is made with fermentation-produced chymosin (FPC), a lab-made version of rennet that helps milk coagulate. The enzyme’s history first developed by Pfizer scientists in 1990 and later sold to Denmark’s Chr. Hansen has become a high-velocity talking point online, largely because it typically does not need to be labeled in a way that distinguishes it from non-engineered alternatives.
Technically, chymosin is the workhorse behind the curd. For centuries, it came from the fourth stomach of an unweaned calf. That supply is inherently limited, and traditional rennet is also a mixture of enzymes rather than a single, tightly controlled ingredient. FPC changed the engineering constraints: isolate the gene for chymosin, insert it into a microorganism, produce it in fermentation tanks, then filter and purify the enzyme. The result is chymosin that manufacturers describe as chemically identical to the calf-derived enzyme, delivered with industrial consistency. Chr. Hansen has described newer generations as a “game changer,” saying they can increase yield by up to 1% from the same milk an efficiency gain that matters in tight-margin dairy operations.
What has not scaled as smoothly is consumer comprehension.
In the U.S., the original regulatory pathway mattered as much as the biology. Pfizer’s product was affirmed as safe under the GRAS framework in the FDA’s final rule for chymosin derived from Escherichia coli K-12, a decision that relied in part on a 90-day rat feeding study. Separately, critics of GRAS have argued that the broader system allows companies to move faster than public oversight, with Michael Taylor, former FDA deputy commissioner for foods, saying in 2014: “We simply do not have the information to vouch for the safety of many of these chemicals.”
Outside the U.S., the conversation often looks more procedural than viral. European regulators evaluate enzyme dossiers and publish detailed safety opinions; for example, EFSA concluded that chymosin from a genetically modified Aspergillus niger strain DSM32805 “does not give rise to safety concerns under the intended conditions of use,” reporting a margin of exposure of at least 10,638. That type of documentation can coexist with continued disagreement about what, exactly, should be disclosed on a label.
Labeling is where engineering choices collide with values. Ingredient panels often use generic terms like “enzymes” or “rennet,” and some packages use “non-animal rennet,” which typically indicates FPC. The American Cheese Society has noted that “ingredient labels do not distinguish” among microbial rennets and other rennet types, leaving people who avoid GMOs or animal-derived inputs to infer production methods indirectly.
For consumers trying to opt out, some cheeses do not require rennet at all fresh styles made by acid coagulation can bypass the enzyme step. USDA-certified organic cheese also prohibits fermentation-produced chymosin, offering a clearer procurement line than most conventional labels. The larger point, though, is not that cheesemaking became “synthetic.” It is that a hidden processing aid became standard infrastructure, and the public is now noticing the plumbing.
