The era of craft cocktails is breaking new ground, as Tamworth Distilling & Mercantile in New Hampshire is releasing a whiskey called "Eau de Musc" flavored with castoreum.

Tamworth Distilling

What's castoreum, you ask? I didn't know either. Turns out, it's the oil from beaver glands that sit just below the beaver's flat tail. Yep, anus oil. From a beaver.

Tamworth's website explains the origin of this bizarre ingredient under their "limited release" spirits section:

The beaver sac spirit is an idea that came from a funny place. As we build recipes, each one has to be reviewed by the TTB. This is common practice and generally bases the acceptance of these formulas on FDA certified ingredients. So if all ingredients land on the FDA generally recognized as safe list, the formula should pass. The generally recognized as safe list (GRAS) is actually pretty small, especially when you are in the exploratory phase of spirits. There are a few really odd ingredients and castoreum is one of them.

While it seems like this would make a truly disgusting taste, Tamworth describes the flavor as being sweet; even my anti-whiskey taste buds are intrigued.

The information on this old timey ‘natural flavoring’ sparked some intrigue and further discovery of the castoreum’s use as a spirit ingredient. The sac excretion exhibits bright and fruit qualities (raspberry) and rich leathery notes along with creamy vanilla aroma. These notes are also very common among barrel aged spirits, so a natural progression took place. From that structure came the addition of woodsy aroma: Birch oil, wild ginger, and fir needles. They are a great way to link the oak barrel components (vanilla, caramel, spice) to the beaver’s contribution. The result is a rich, full bodied 2-year bourbon that bolsters a vanillic nose and fruity, floral finish — a medley of charming flavors that are sure to impress.

I gotta admit, I was extremely skeptical, but that description's got me wondering if this might just be one of those "don't need to see how the sausage is made" things.