Pfizer Quietly Took Over the World's Cheese Supply

On February 9, 1988, Pfizer filed an ingredient approval petition with the FDA. The ingredient was called Chymax. To make it, scientists took a gene out of a cow, spliced it into E. coli (the same category of bacteria behind every food poisoning outbreak you've ever read about), and grew the enzyme in industrial fermentation vats. Nothing like it had ever been approved for human consumption. Nobody actually expected it to go through.

Two years later, on March 23, 1990, the FDA quietly approved it. The ruling appeared in the Federal Register, Vol. 55, No. 57, pages 10932 to 10936. With that approval, Pfizer became the company behind the first genetically engineered organism ever greenlit for human food. Today, 36 years later, that same enzyme is in roughly 90% of American cheese and most of the world's cheese. You've never seen it on a single label.

The 8,000-year-old process Pfizer replaced

For 8,000 years, cheese was made one way. You take milk and add a small amount of an enzyme called rennet, which traditionally comes from the stomach of a young calf. Inside milk there's a protein called casein, and casein floats around in tiny protein balls called micelles, each coated in a protective layer. Rennet acts like molecular scissors. It snips that coating off, the micelles clump together, and the milk turns into cheese.

That was the entire process. Cheddar, parmesan, gouda, brie, feta. Every cheese you've ever heard of, for almost all of recorded history, was made this way.

Then in the 1980s a scandal broke. The calves rennet came from were being kept in tiny stalls that prevented them from turning around or lying down. The public response was massive. Veal consumption across North America collapsed by over 90% from its peak. The New York Times called it "the most successful animal rights boycott in U.S. history." Fewer veal calves meant fewer calf stomachs, which meant the price of rennet skyrocketed.

Pfizer noticed.

The patent and the GRAS loophole

On October 20, 1984, Pfizer filed patent US 4,935,370, officially titled "Expression plasmids for improved production of heterologous protein in bacteria." They isolated the gene in calves that produces chymosin, spliced it into E. coli, grew the bacteria in giant fermentation tanks, and filtered the enzyme out the other end. They called the product Chymax.

On February 9, 1988, they filed GRASP 8G0337. This was a petition asking the FDA to declare their lab-made enzyme "Generally Recognized as Safe," meaning so obviously safe it could go into food without any of the testing or approval normal new ingredients require.

Here's the thing. The entire safety case rested on two studies. A 30-day rat study and a 5-day dog study. Both were submitted only to the FDA. Neither was ever published in a peer-reviewed journal, so independent scientists couldn't review them at the time. The legal argument Pfizer made was something called "substantial equivalence." They submitted 15 studies arguing that because the amino acid sequence of their lab-made chymosin matched the sequence of chymosin from a calf, no separate safety evaluation was needed.

The FDA agreed. On March 23, 1990, they approved it. There was almost no public attention, because almost no one knew it had happened. Within 10 years, Chymax was estimated to be in roughly 60% of US hard cheeses.

Why nobody connects this to Pfizer

In 1996, Pfizer sold its entire food enzyme and cheesemaking division to Chr. Hansen, a Danish bioscience company. Pfizer's name left the public-facing supply chain immediately. The product didn't go anywhere.

Chr. Hansen has since released newer versions. The original E. coli-based Chymax is still in use, but they've expanded into versions produced from other genetically modified microorganisms. Most commonly Aspergillus niger (a fungus) and Kluyveromyces lactis (a yeast). The process is essentially the same as Pfizer's original. The microorganism is grown in a fermentation tank, and the enzyme is purified out at the end.

Here's where the loophole gets interesting. Because the final product is purified, the company says the genetically modified organism itself is no longer present in the cheese. Therefore, in their view, the cheese contains no GMO. That classification means it's exempt from the 2016 federal GMO labeling law, the same law that requires every other GMO ingredient in your food to be disclosed. So unlike literally every other GMO product on US shelves, this one can be hidden completely.

The Aspergillus niger problem

Aspergillus niger, the fungus Chr. Hansen now uses to produce most of its rennet, has a reputation problem. When fermented, it's a known producer of a chemical called ochratoxin A.

The International Agency for Research on Cancer has classified ochratoxin A as a Group 2B carcinogen, meaning "possibly carcinogenic to humans." The U.S. National Toxicology Program goes further, designating it as "reasonably anticipated to be a human carcinogen," based on what they describe as sufficient evidence of carcinogenicity in experimental animals.

A 2024 study published in Archives of Toxicology gave mice daily oral doses of ochratoxin A for up to 7 days. The researchers found dose-dependent damage in both the liver and kidneys. The animals showed necrosis (uncontrolled cell death) and apoptosis (programmed cell death), and the highest doses triggered necroptosis, another form of programmed cell death only recently discovered.

The industry defense

The industry's response is specific. They say the particular strains of Aspergillus niger used in cheese production are selected to not produce ochratoxin A. They argue that only some strains can produce the toxin, and that food enzyme producers screen out the toxin-producing ones. They also point out that the enzyme is purified after fermentation, so any trace residues should be removed.

The problem is verification. Industry-independent groups have noted there is no standardized public method for confirming how completely the modified microorganism is removed from the final enzyme. The screening claim, the purification claim, all of it relies on the company's own internal process.

The bigger issue is that we don't actually know if this ingredient is harmful, because it was approved through the GRAS self-certification process and never required independent safety testing. There simply isn't enough data, 36 years in, for anyone to say with confidence either way.

What this means for what's in your fridge

The artificial rennet is banned in Europe's most iconic traditional cheeses, which are legally required to be made with animal rennet from calves. It's in commercial cheese around the world. It's almost certainly in your cheddar.

In my opinion, the most disturbing part of this isn't even the toxin question. It's the transparency. People should have the right to know what they're buying so they can make an informed choice. Cheeses made with this ingredient don't have to disclose it, and the labels they do use are almost designed to read as natural. "Enzymes." "Vegetable rennet." "Vegetarian rennet." "Non-animal rennet." Even just "rennet" on its own. None of those words sound synthetic. All of them very likely point to the lab-made version.

What I'm going to do is read the back of the label. If it says "animal rennet," "calf rennet," or "traditional rennet," I'm good. Those are the only terms that guarantee the real thing. Everything else, in the cheese aisle of any major supermarket, is very likely a Pfizer-engineered organism that the FDA approved on a 30-day rat study. That gives you the choice when you're standing there. The 8,000-year-old version, or the one nobody told you about.