How Animal Advocates (Inadvertently) Helped Launch Synthetic Biology Rennet in Cheese

Paul Shapiro
5 min readJan 21, 2021


Rather than using rennet from a calf’s stomach, nearly all cheese today is made using synthetic biology. Such a biotech fermentation product can compete on cost only because the veal industry was decimated.

By Paul Shapiro

Often when alt-protein advocates make the case that biotech food startups can succeed with products like Perfect Day’s non-animal whey and Clara Foods’ non-animal egg proteins, the widespread displacement of rennet in cheese is Exhibit A. For millennia, calf-based rennet was used to make cheese, and now nearly all cheese contains a synthetic biology-produced (synbio) version instead. If calf rennet’s dominance in cheese-making could so quickly be supplanted by synbio fermentation, could the same happen for other animal-based ingredients?

It turns out that the story of rennet’s displacement is even more interesting than it appears. I was formerly under the impression that synbio alternatives to rennet were simply more efficient than rennet. But after a conversation with Irina Gerry led me to research more, I learned that the animal protection movement actually inadvertently had as much to do with rennet becoming much more expensive as biotech companies like Pfizer had to do with bringing the cost of synbio rennet alternatives down.

When Animal-Use Industries Recede into History

It’s hard to think of many industries that have ended as a result of pleas from animal advocates. In fact, it’s far easier to enumerate such industries that have been decimated not by humane concerns, but by new technology simply rendering the animal exploitation obsolete. For example:

  • Geese are no longer live-plucked for their quills not because anyone crusaded for the birds, but because metal fountain pens were invented.
  • We no longer use carrier pigeons not because we cared about the pigeons, but because the telegraph was invented.
  • Fireflies are no longer “harvested” by the millions for the biotech industry not because it was unsustainable, but because scientists synthesized luciferase.
  • Humanity (largely) stopped exploiting horses for labor not because of animal advocates’ campaigns to garner horses better working conditions, but because of the invention of the internal combustion engine.
  • Our homes are no longer lit by whale oil not because 19th century social reformers gave whales a voice, but because kerosene liberated whales from harpoons.

There is at least one example, however, where humane concerns have essentially eradicated an industry.

When Animal Advocates’ Pleas Fell on Willing Ears

After Peter Singer’s seminal book Animal Liberation was published in 1975, the new animal protection movement it spawned made the veal calf its poster child (poster calf?) and crusaded to make veal consumption taboo. The result: per person veal consumption plummeted. When Singer’s book came out, on average each American ate about 5.0 pounds of veal per year. Due mostly to animal welfare concerns, that number has now dropped to around 0.2 pounds, nearly ending the veal industry. (Male dairy calves who would’ve been slaughtered for veal are now typically raised and slaughtered for beef instead.)

The effect of this shift was not only to alter the fate of male dairy calves, but also to nearly end the use of rennet in cheese.

A Curd in the Bioreactor is Better than Two in the Calf’s Stomach

For millennia, milk had been made to coagulate into cheese by adding rennet to it. Traditionally that rennet came from the lining of the fourth stomach of a very young calf.

But with veal demand in such precipitous decline, the number of young calf stomachs available to the cheese industry also plummeted, forcing rennet prices skyward. Or as Gizmodo more aptly put it: “In the 1970s, America’s growing appetite for cheese collided with its mounting aversion to killing newborn cows.”

The Vegetarian Resource Group notes that necessity became the mother of invention for the cheese industry. “When calf rennet became scarce and unreliably available in the 1960s and 70s as the veal industry was declining due to the animal rights movement but demand for cheese increased, calf rennet became very expensive. Companies looked for a ‘rennet substitute.’”

As chymosin is the primary enzyme in rennet responsible for curdling, in the 1980s, Pfizer began experimenting with genetically engineering microbes to produce chymosin without the calf. And in 1990, their “fermentation-produced chymosin” (FPC) became the first genetically engineered food the FDA approved. Today, FPC produced through synbio has replaced rennet in about 90 percent of American cheese. (Interestingly, some cheese-makers use plant-based coagulants as a rennet substitute rather than FPC.)

In a 1990 New York Times article about the FDA’s approval of FPC, an FDA spokesperson made the point clear: “‘The real advantage is that it is probably a much cheaper way of producing this substance than to grow calves.”

A Los Angeles Times article from the same time notes that the cheese industry welcomed Pfizer’s invention, as calf-derived rennet “has soared in price in recent years.” It further noted that Pfizer was “promising a lower price than the natural version.”

Today, numerous companies sell synbio FPC, from DSM to Chr. Hansen to Danisco and more. These FPC offerings are purer, more reliable, and more affordable than rennet from a calf’s stomach. Additionally, there are now other microbial alternatives to FPC that are allegedly even cheaper, made by companies like Dupont. In the same way kerosene replaced whale oil only later to be replaced by electric lightbulbs, perhaps such microbial coagulants will render FPC obsolete one day.

Wheying the Evidence

There are many lessons to take from the story of rennet’s displacement by FPC, but one that seems obvious, to me at least, is that price is paramount when it comes to food. So much is said about whether synbio proteins like Perfect Day and Clara Foods will ever be able to come down in cost to reach price parity with commodity dairy and eggs. But, as in the case with rennet, it could be that increasing prices for conventional animal products will be part of the equation, rather than solely cost reduction for the newcomer alternatives.

For example, resource scarcity could lead to meat price hikes, and we could have shortages as occurred during the 2020 pandemic. Federal or state excise taxes on meat (similar to gasoline, tobacco, alcohol, and luxury vehicles) could also play a role. Or ending subsidies for animal feeds like corn and soy. Or internalizing costs like environmental degradation that are associated with livestock production.

Those of us working to mainstream alternative protein products should heed the lesson of rennet. Sometimes a product may end up competing on cost not just because it’s more efficient, but also because the competition just can’t keep its prices low.

Paul Shapiro is the author of the national bestseller Clean Meat: How Growing Meat Without Animals Will Revolutionize Dinner and the World, the CEO of The Better Meat Co., a four-time TEDx speaker, and the host of the Business for Good Podcast.



Paul Shapiro

Husband of Toni Okamoto. Author of nat’l bestseller Clean Meat. CEO of The Better Meat Co. Host of Business for Good Podcast. 4x TEDx speaker.