I’m a historian who writes about the flavor industry. This means I’ve witnessed firsthand the weird obsession some people have with castoreum, a beaver-gland-derived flavor ingredient, and the notion that we are all unwittingly eating beaver butt juice. Vani Hari, the health-and-wellness blogger known as the Food Babe, didn’t start this fire, but she’s certainly fanned its flames. In a video on her YouTube channel , she sits on a log, chatting up a stuffed beaver doll. Beavers, she says, “flavor a ton of foods at the grocery store with their little butthole.” Over a close-up of a beaver’s anus—a puckered hole ringed with chestnut fur—Hari explains that castoreum is considered a “natural flavor” by the FDA. “It’s far cheaper to use castoreum, or beaver’s butt, to flavor strawberry oatmeal than using actual strawberries,” she claims, without providing any numbers to support this assertion.

According to nature writer Ben Goldfarb, author of Eager: The Surprising Secret Life of Beavers and Why They Matter, the demand for castoreum wiped out most of the beavers in Europe by the end of the Middle Ages. When Europeans settled North America, with its abundant supply of beavers, they had another use for the animal: beaver-fur hats. Living beavers, a keystone species, helped build the American landscape; dead beavers provided a foundation for American capital accumulation, and helped fund Western colonization. The Astors made their original fortune in beavers, before getting into Manhattan real estate.

Humans have a long history of consuming castoreum. Since antiquity, it’s been hailed as a powerful medicine, a treatment for everything from epilepsy to constipation to spider bites. Roman women inhaled the fumes of smoldering castoreum in an attempt to induce abortions. Francis Bacon, the 16th-century English polymath, recommended snorting a bit of powdered castoreum as a cure for brain-fog.

So when I heard there was a new bourbon flavored with castoreum, I knew I had to try it.

I get how the anal adjacency of these glandular secretions makes castoreum repulsive to many people. But if it was being used in flavorings, I knew there was only one reason for it: It must be delicious. I also knew, from conversations I’d had with people who work in the flavor industry, that it was increasingly rare. Decades ago, you may have caught a whiff of castoreum in fancy store-bought vanilla ice cream, or tarting up some raspberry-flavored chocolate bon-bons. But the chance that there’s any beaver butt lurking in today’s “natural flavors” is vanishingly small.

Castoreum—a classy, antique-sounding word, jazzed up by its neat near-rhyme with “santorum”—stands in for all of the bizarre, filthy, and perverse things that “they,” the corporate monsters of processed snacks, are doing to your food. While Hari is correct that castoreum is classified as a natural flavor, she’s wrong about basically everything else. No, castoreum is not a cheap substitute for strawberries; it’s a luxe, artisanal material. And it’s not beaver butt; technically, it’s not even from beaver anal glands. Sure, the castor sacs are right next to the anal glands, but while anal excretions smell like motor oil (in male beavs) or rancid cheese (in the ladies), the yellowish oily fluid in the castors gets its fragrance from plant compounds concentrated from beavers’ wild diets. It’s basically beaver-made herbal essences.

Aftel, who also makes a line of chef’s flavorings, has not used castoreum in edible concoctions, but points out that other heavily scented animal glands and secretions—musk, civet, and ambergris—were luxury ingredients in Medieval banquets. The 15th-century Persian Ni’matnamah, knows in English as the Sultan’s Book of Delights, includes recipes for musk-spiced samosas and ambergris-and-rosewater puddings.

The American beaver trade brought castoreum back into the spotlight, this time as a perfume. The perfumer-historian Mandy Aftel described it to me as “kind of sexy, kind of dark”—the scent of Russian leather. “It’s what’s known as a base note,” she explained. “It’s deep under things, one of the last lingering notes you smell.”

In the 1980s, the use of castoreum in flavors began to lag. In 1982, according to the Flavor Extract Manufacturers’ Association (FEMA), 683 pounds of castoreum were used in flavorings in the US. In 1987, that had dropped to just under 250 pounds. FEMA couldn’t provide me with current figures, but confirmed that its use has “decreased significantly” since then. Tobacco industry memos suggest that cigarette makers have also largely abandoned the substance.

Castoreum was never fake vanilla or fake strawberry—not exactly. It was used in tiny amounts, usually less than ten parts per million, adding depth, intricacy, and intrigue to flavor compositions. In this way, castoreum is a quintessential secret ingredient, something that made a flavor better and more interesting, while eluding recognition.

In 1982, according to the Flavor Extract Manufacturers’ Association (FEMA), 683 pounds of castoreum were used in flavorings in the US. In 1987, that had dropped to just under 250 pounds.

Castoreum began to be used in flavorings in the early 20th century, an era when flavor-makers were borrowing freely from perfumers’ toolkits. By the 1960s, it was being used in vanilla and fruity blends; a 1970s flavor textbook praised the “unusual notes” it added to strawberry and raspberry flavors. Castoreum could be found in beverages, baked goods, ice cream, candy, and especially in chewing gum. The Algonquins traditionally dusted their tobacco with dried castoreum, and, in the 20th century, so did cigarette manufacturers like Phillip Morris and RJ Reynolds; it gave Camels and Winstons a distinguished, luxe aroma.

Tamworth Distilling, makers of Art in the Age spirits and other heritage-hipster libations, were inspired to make a spirit with castoreum when they noticed it on the GRAS list, the tally of “generally regarded as safe” ingredients the FDA allows in food. Their Eau de Musc, released this summer, is a bourbon flavored with castoreum along with regional White Mountain botanicals: fir tips, sweet birch, wild ginger, Canadian snakeroot. It’s “the mood of the forest,” evoking both the beaver and its woodland home, according to Matt Power, a master distiller at Tamworth who helped develop the beverage.

And just like that, one of industrial food’s arcane delights faded, unheralded, from the food supply—decades before people started freaking out about it.

Susie Bautista, a flavorist who worked in the industry in the 1990s, remembers an assignment she was given to remove the beaver butt from a vanilla flavor for a client that wanted to go kosher. She had never worked with castoreum before, and so she sampled the flavor with and without it. “When you tried them side by side,” she recalls, “castoreum added a lot of body. It was sweet, sweet and full.”

In some cases, genuine castoreum was probably replaced with cheaper synthetic chemicals. But the biggest problem with castoreum was not its price, nor its anal-adjacent origins. It’s that beaver butt is not kosher. If food companies wanted to earn the rabbinical seal of approval, any traces of castoreum in flavorings had to be nixed.

There is a traditional castoreum-flavored spirit: Bäverhojt, a schnapps typically consumed by Swedish trappers before heading out for a day hunting game. Tamworth distiller Jamie Oakes made the untraditional decision to infuse it in bourbon, he told me, because of its “raspberry sharpness and vanilla-creamy, birchy kind of aroma.”

Tamworth gets its castoreum from Anton Kaska, a local New Hampshire trapper, who harvests castor sacs from nuisance beavers he’s hired to destroy.

“I sell a plastic shopping bag full of dried frozen castors every month,” he told me, though he couldn’t quite say who’s buying them or why. “We don’t talk about who they are.”

Beavers are ferociously territorial, and castoreum is how they mark their territory. They build muddy mounds “about the size of an upside-down cocktail glass,” Kaska told me, back up to them, and squirt castoreum from out their glorious, multipurpose buttholes. To a beaver, castoreum is a complex chemical stew, one that advertises a beaver’s clan and tells non-relatives to keep out.

Castoreum may be “beaver butt” to the Food Babe, but the castoreum used in flavorings and perfumes never exits through the anus. Kaska extracts the intact sacs from the bellies of dead beavers. Some flavorists I spoke with semi-affectionately called it “beaver balls,” and castor sacs do look remarkably testicular—two pendulous blobs, brown and wrinkled like dried figs, connected by a thin tube. The castoreum mellows as the castors are dried, but it remains potent: The entire 500-bottle batch of Eau de Musc was flavored with the castors from a single beaver. “It smells like an old cowboy,” Kaska said to me.

Tamworth Distillers are not the only people buying castors from Kaska. “I sell a plastic shopping bag full of dried frozen castors every month,” he told me, though he couldn’t quite say who’s buying them or why. “We don’t talk about who they are,” he said. He also sells them on his Etsy shop.

Kaska finds himself killing more beavers lately. The price of pelts has collapsed, and with fewer hobby hunters to keep the population in check, beaver dams are a growing problem, flooding houses and washing out roads. He relocates beavers when he can, but crowded beavers slaughter each other over territory, or waste away from disease. Hunting them is kinder, he says. Nature is out of balance.