Many Americans have been taken aback after discovering that nearly 90% of cheese in the United States contains a lab-produced enzyme from Pfizer, which doesn’t require labeling.

This enzyme, known as fermentation-produced chymosin (FPC), is a genetically engineered form of rennet, traditionally used to curdle milk in the cheese-making process.

Although FPC has been a staple in cheese production for decades, a recent viral post on social media has reignited discussions about its origins. The post has led to widespread criticism and demands for clearer labeling practices.

On social media platform X, one concerned user questioned, “How is this allowed?” while others pledged to avoid American-made cheese altogether.

Another individual expressed their thoughts, stating, “I believe in transparency on cheese ingredient lists. The lab-created rennet should be identified as pseudo-rennet. Personally, I prefer cheese without any artificial additives.”

FPC was developed in 1990, when Pfizer scientists engineered a microorganism to produce chymosin, the key enzyme found in calf rennet. 

The innovation revolutionized cheesemaking by making the process cheaper, faster  and more consistent, but it also introduced genetically engineered material into one of America’s most widely consumed foods.

The US Food and Drug Administration (FDA) approved FPC as ‘Generally Recognized as Safe’ (GRAS), a regulatory designation that allows substances to enter the food supply without full pre-market approval. 

The FDA’s decision relied in part on a 90-day rat feeding study, a fact that critics have cited as evidence of insufficient long-term safety testing.

Americans have been left stunned after learning that nearly 90 percent of US cheese contains a lab-made enzyme from Pfizer, and it does not have to be labeled

In 1996, Pfizer sold its cheesemaking division to the Danish bioscience company Chr Hansen, which continues to manufacture and supply the enzyme to major US dairy producers. 

Chr Hansen has emphasized that FPC is more predictable, efficient and scalable than traditional rennet, helping it become the dominant enzyme in global cheese production. 

Jacob Vishof Paulsen, the company’s EVP of EMEA & North America, previously described newer versions of the enzyme as a ‘game changer,’ noting they allow cheesemakers to extract up to one percent more yield from the same amount of milk, a significant gain in an industry with tight margins.

Daily Mail has contacted Chr Hansen for comment. 

Despite these efficiencies, consumer advocates have argued that the lack of transparent labeling is the real issue. 

The American Cheese Society has acknowledged that FPC is a genetically modified organism.

However, ingredient labels do not distinguish between genetically engineered rennet and non-GMO alternatives.

Some companies list ‘non-animal rennet’ on the packaging, which means it contains FPC. 

Scientists and regulators counter that genetically engineered food enzymes like FPC pose no greater risk than conventional foods. 

Organizations such as the World Health Organization and the European Food Safety Authority have long supported the safety of properly tested GMO products. 

The ingredient, known as fermentation-produced chymosin (FPC), is a genetically engineered version of rennet, an enzyme used to coagulate milk during cheesemaking

However, critics have argued that safety assurances mean little without informed consumer consent.

Some cheeses do not require rennet at all, including cottage cheese, cream cheese, paneer, and certain types of mozzarella, which are made using acid or alternative coagulants. 

USDA-certified organic cheese also prohibits the use of fermentation-produced chymosin, making it an option for consumers seeking to avoid the enzyme.

While the FDA continues to stand by its GRAS determination, the uproar highlights a broader debate over food regulation. 

Under US law, GRAS substances do not require FDA approval or notification before marketing. 

Former FDA Deputy Commissioner for Foods Michael Taylor acknowledged flaws in the system in 2014, stating: ‘We simply do not have the information to vouch for the safety of many of these chemicals.’ 

Cheesemakers can use several different forms of rennet, but for hundreds of years, animal-based rennet was the standard. 

This traditional rennet is extracted from the fourth stomach lining of an unweaned calf, where the enzyme naturally helps young animals digest milk. 

Because calves produce far higher concentrations of rennet than adult cattle, the enzyme must be harvested early in the animal’s life.

The extracted rennet is not pure chymosin, as it typically contains a mixture of chymosin, pepsin and other proteins. 

Since rennet can be obtained only once from a single calf, supply is limited, and production costs are high. As demand for cheese surged in the late 20th century, the industry increasingly viewed animal rennet as inefficient and unsustainable.

And FPC offered a solution with scientists isolating the gene responsible for chymosin production and inserting it into a microorganism such as bacteria, yeast or mold. 

The organism is then grown in large fermentation tanks, producing chymosin in bulk. After fermentation, the enzyme is filtered and purified, resulting in chymosin that is chemically identical to the enzyme found in calves, without the need for animal slaughter.