Is precision fermentation GMO, and is it safe?

The objection

“These are unnatural, GMO Frankenfoods cooked up in a lab. I’ll stick to real food.”

The answer

The GMO part is accurate. Precision fermentation puts a gene for the protein you want, often copied from the animal’s own genome, into a yeast, fungus or bacterium, grows the microbe in a fermenter and separates the protein from the broth (Purba and Sangsawad, 2025) [5]. The objection goes wrong in treating the method as new and untried.

How long has precision fermentation been used?

Precision fermentation has been used in medicine since 1982 and in food since 1990. From the 1920s people with diabetes were treated with insulin purified from cattle and pig pancreases [1], which differs in its amino acid structure from the insulin a human body makes (GFI Europe, 2026) [4]. Insulin made by modified E. coli was approved in the US in 1982 [1][3]. Those first recombinant insulins had the same amino acid sequence as the human hormone, a closer match than the animal insulin they replaced, and insulin is now made mainly in E. coli and yeast (Baeshen and colleagues, 2014) [1].

Food followed in March 1990, when the US Food and Drug Administration affirmed as safe a chymosin made by modified E. coli, for curdling milk into cheese [2]. Chymosin is the active enzyme in rennet, which the same regulation describes as an extract of the fourth stomachs of calves, kids or lambs [2]. The Vegetarian Resource Group, a US non-profit, called the enzyme the first bioengineered product permitted in American food, and reported in 2012 that enzyme companies and dairy groups attributed 90% of US commercial cheese to it [3]. The Good Food Institute Europe, which promotes alternative proteins, puts microbe-made chymosin in around 80% of the cheese eaten worldwide (2026) [4]. Anyone who eats cheese has very probably eaten the work of a genetically modified microbe.

Is there anything genetically modified in the food?

The genetically modified microbe isn’t meant to end up in the food: it makes the protein, which is then separated from it [5]. Perfect Day, a US company that makes whey proteins this way, says its protein is separated from the microbes, then filtered, purified and dried (2021) [6], and US rules for the 1990 chymosin require acid treatment “to destroy residual cellular material” [2].

Is precision-fermented protein safe to eat?

In 2020 the FDA had no questions about Perfect Day’s conclusion that its brewed whey protein, beta-lactoglobulin made by the fungus Trichoderma reesei, is generally recognised as safe in food [7], but that protein is still a milk allergen. Perfect Day told the FDA that because it is identical to the beta-lactoglobulin in cow’s milk it will cause a reaction in people allergic to milk, and the FDA’s reply notes that US law requires foods containing it to declare milk on the label [8]. Anyone with a cow’s milk allergy should treat these foods as dairy. Telling the FDA was Perfect Day’s choice: under current US rules a company that concludes its ingredient is generally recognised as safe may notify the FDA but doesn’t have to, and in August 2026 the FDA proposed making notification compulsory [9]. In the EU, most milk proteins made this way count as novel foods, which the European Food Safety Authority must assess before they can be sold (Purba and Sangsawad, 2025) [5].

Is fermented whey or casein the same as the cow’s?

A single brewed whey protein can match the cow’s in sequence, but casein is much harder to copy. Perfect Day concluded from its protein data, as the FDA’s 2020 letter records, that its beta-lactoglobulin has the same sequence as the one sold from cow’s milk [8]. The trouble with casein is that a cow’s mammary cells attach phosphate groups and sugar chains to it after it is made, and a 2025 review says that in a brewed casein these depend on the microbe doing the work, which it calls a major hurdle [5]. The review also says milk proteins made outside the animal often come out with changes in their amino acid chains, and that rebuilding the casein micelle, the cluster of proteins that rennet makes curdle into cheese, remains a substantial barrier, though a single protein such as beta-lactoglobulin can already do particular jobs, such as foaming and emulsifying, on its own [5].