If you’ve been on the internet in recent years, you might have seen the claim that artificial vanilla flavoring found in cookies or ice cream comes from goo secreted out of beaver behinds. Every few years, posts go viral on social media warning consumers that this substance—called castoreum—may be disguised as “natural flavoring” on the ingredient list of your favorite sweet treats.
While this statement is not entirely false—beavers do excrete sweet-smelling (and edible) castoreum from sacs near their anuses—experts say you probably can’t find this goo on the shelves of your nearest grocery store.
“It turns out that the stuff is incredibly expensive, because it’s rare,” Michelle Francl, a chemist at Bryn Mawr College who studies the science of food, tells National Geographic’s Jessica Taylor Price. “There’s no way it’s in your ice cream.”
Castoreum is a yellowish-brown substance located in beavers’ castor sacs, which are found between the pelvis and the base of the tail. The animals mark their territories by building piles of mud, sticks or grass along the water’s edge and secreting castoreum on top. These “castor mounds” give off scents strong enough that humans can easily detect them.
“It’s a very distinctive smell, castoreum … it’s kind of musky, but sweet,” Roisin Campbell-Palmer, head of restoration at Beaver Trust, a U.K.-based beaver conservation organization, tells National Geographic. The secretion’s powerful aroma comes from the plants in beavers’ diets, as flavor historian Nadia Berenstein wrote for Vice in 2018.
Humans have been using castoreum for more than 2,000 years, mostly to cure ailments like headaches, earaches, toothaches, fevers and gout. The Romans burned castoreum in lamps, believing the fumes caused abortions. It has also been used extensively in perfumery to add a leathery scent and as a lure for beaver trapping. But removing castoreum from beavers is a labor-intensive process. First, the animals must be anesthetized, then their castor glands must be “milked.”
“You can squirt [castoreum] out,” wildlife ecologist Joanne Crawford told Mollie Bloudoff-Indelicato of National Geographic back in 2013. “It’s pretty gross.” The substance can also be harvested from dead beavers if their castor sacs are removed and left to dry.
In the early 20th century, castoreum began appearing in some foods to add a vanilla-raspberry flavor. But its use had fallen by 1987, when the U.S. consumed about 250 pounds of castoreum per year, according to Vice. Since then, its use has “decreased significantly,” as the Flavor Extract Manufacturers’ Association told the publication. Perhaps the final strike against popular use of castoreum was that products using it as flavoring could not be certified as kosher.
Now, the substance is mostly found in niche foods such as a Swedish liquor. Instead, about 99 percent of the world’s vanilla comes from synthetic sources such as vanillin, a cheaper and less labor-intensive alternative to harvesting vanilla beans or castoreum.
So, while the Food and Drug Administration does list castoreum as safe to eat, it’s unlikely you’ll ever have to worry about ingesting beaver butt goo by accident.
“If you think about this from an economic and supply chain perspective, there is no commercial source of beaver castor sacs,” Robert J. McGorrin, a flavor chemist at Oregon State University, tells Business Insider’s Rebecca Strong.