Castoreum: The Beaver That Never Castrated Itself

A saddle left too near the woodstove in a log cabin gives up birch smoke and hot tar first, then warm hide. Under the hide sits something sweeter and harder to place, like raspberry jam gone dark on the back of the stove, and it makes the leather smell as if it still belonged to an animal.

In a perfume, that last layer is castoreum, which comes from two dried sacs a beaver carries near the base of its tail. From Aesop to the medieval bestiaries, writers told a story about those sacs that the beaver's own body disproves. The newer story, that castoreum flavours vanilla ice cream, was true for decades and is almost never true in a grocery store now.

The hunter calls off the chase

Aesop has a beaver chased by dogs bite off its own testicles, knowing that is what it is hunted for, and the hunter calls off the chase. Aelian improved on it: his beaver throws them in the hunters' path, like a prudent man who falls among robbers and gives up all he carries to save his life. Isidore of Seville, in the seventh century, built the Latin name on the story: castor, he wrote, because it is castrated. Around 1200 the Aberdeen Bestiary drew a sermon from it: cut off your vices and throw them in the devil's face.

The story had doubters early: the physician Sextius, cited by Bartholomaeus Anglicus, said the parts cling so close to the backbone that they cannot be taken without killing the animal. Albertus Magnus, in the thirteenth century, called the tale "absolutely false" and put the name down to the hunters, who did the cutting. Thomas of Cantimpré recorded that the Poles rejected it because a beaver's testicles do not hang outside the body. They lie inside the belly.

Two sacs at the base of the tail

What the hunters were after lies under the skin between the pelvis and the base of the tail, where two cavities hold a pair of castor sacs beside a pair of anal glands. The sacs are often called glands, and strictly they are not. With the testicles hidden inside the body and the sacs close to the tail, many people took one for the other.

Every version of the legend is about testicles, and female beavers carry the very same sacs. In an ordinary beaver they weigh around 250 grams. A trapper finds them by cutting two inches above the vent, where they lie under a thin membrane of muscle, light brown and scaly.

Seven days on a knotted string

In 2022 the Northwest Territories began taking dried beaver castors from its trappers alongside their furs, with an advance on every pound, about eight castors to the pound. The castors come from trapped beavers and are removed at skinning.

The territory's reference sheet for trappers, issued that March, reads like a curing recipe: the castors go on a string knotted every four inches and stretched between two nails in the skinning shed, at 15 to 21 degrees Celsius, for about seven days. After two days each one is opened so the centre can dry and turned inside out, then flipped again after four days and after six. Dried castors are frozen in a paper or onion bag, never plastic, in which they rot and lose all value. "Castors need to breathe."

Then the sacs are left to age, usually two years or more, to mellow before they are crushed and extracted with alcohol. Perfumers use the result as a tincture or as a resinoid.

Castoreum was worth faking long before any reference sheet. In the thirteenth century Bartholomaeus Anglicus warned of forgeries: an animal's bladder filled with blood, with a little castoreum for the smell and pepper for the bite. The genuine article, he wrote, is double and hangs from one sinew, because two bladders cannot hang from one neck.

From birch tar to raspberry

Steffen Arctander gave the tincture a "warm, animal, leather-like sweet odour", and the two grades pull those words apart. In one supplier's hands the Siberian, long ranked below the Canadian, opens on smoky, tarry leather close to birch tar and creosote before a musky animal heart, drier than the Canadian and with less fruit. The Canadian is gentler on smoke and closer to what most people know as castoreum, and the Northwest Territories, whose trappers dry theirs on knotted strings, credits castoreum with raspberry and vanilla as well as leather.

Perfumers use castoreum mostly to build leather, and rarely alone.

Leather Don is the woodstove's opposite, a light leather for warm weather from Lost Tribe, the all-natural New York house. The leather accord alone takes 13 natural ingredients, and under it sits a Cambodian oud from Koh Kong, macerated and aged with real castoreum. Lemon and cool eucalyptus open it, hay and a little tobacco come up through the leather, and the oud gives it an animal depth from underneath, over patchouli and oakmoss.

The ice cream scare

The rumour that the vanilla in ice cream comes from a beaver has a true root. Castoreum once flavoured ice creams, sodas and candy, and by 2007 it had been a food flavouring for at least 80 years. In the United States it is still on the list of natural extracts generally recognised as safe, in the same short table as ambergris and Tonkin musk.

The amounts are tiny: around 100 kilograms a year, against more than 1.2 million kilograms of vanillin. Almost nothing in a grocery store contains it today, and Michelle Francl, a chemist at Bryn Mawr College, says "there's no way it's in your ice cream". It turns up instead in curiosities such as bäversnaps, a Swedish spirit.

Beside the musk

The next two bottles keep castoreum in the base beside musk: Tonkin musk in the first, and in the second vintage deer musk, which comes from another animal and another organ altogether.

EO2 Tonkin is a spiced, sweaty musk from Ensar Oud. Coriander, cumin, Sichuan pepper and pink pepper open it, and the cumin and helichrysum are musked out, drunk on black tea and castoreum. Jasmine sambac, rose otto and blackcurrant fill the heart, the blackcurrant a sweetener that teases out the musk's treacle-like bite. Underneath, castoreum shares the base with old black Tonkin musk, wild Kepi agarwood, sandalwood and beeswax.

Russian Adam, the agarwood distiller who founded Areej Le Doré, worked castoreum into a co-absolute he made himself with vintage deer musk, ambergris and vintage civet, and set it on Indian oud, oakmoss and Indonesian vetiver. Together the four animals turn the perfume toward aged leather and untamed wilderness. Vintage Taif rose and powdery orris sit above that dark, leathery base.

Along the rivers, beavers still pile mud on the ground and leave castoreum on top to mark their territory. Róisín Campbell-Palmer of the UK's Beaver Trust calls castoreum "kind of musky, but sweet", and says that even if you don't see beavers about, you know they're there.

Frequently asked questions

What is castoreum in perfume?

In perfumery, castoreum is an alcohol extract of the beaver's dried castor sacs, used as a tincture or a resinoid. Male and female beavers both carry the sacs, under the skin between the pelvis and the base of the tail. Perfumers use it mainly for a note that suggests leather, blended with other materials.

Did beavers really bite off their own testicles?

No. The story runs from Aesop and Pliny to Isidore of Seville and the medieval bestiaries, and Albertus Magnus called it absolutely false in the thirteenth century. The castor sacs are not testicles, and female beavers have them too.

Is castoreum in vanilla ice cream?

It was once used often to flavour ice creams, sodas and candy, but annual use is very low, around 100 kilograms, against more than 1.2 million kilograms of vanillin. Almost nothing in a grocery store today contains it.

How is castoreum made?

Trappers remove the castor sacs at skinning and dry them; in the Northwest Territories that means about seven days on a knotted string in the skinning shed. The dried sacs are generally aged two years or more to mellow, then crushed and extracted with alcohol for use in perfume as a tincture or a resinoid.