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Whether their drink of choice is cognac, whiskey, vodka, or tequila, some people love a little liquor now and then. And as it turns out, people aren’t the only ones—the walls of many of the distilleries where these drinks are made are coated with a kind of black fungus that thrives on the alcohol evaporating from the wooden casks.
For a long time, we’ve thought of this fungus as mostly harmless, if a bit off-putting—until, that is, it started to spread. Since the early days of distilling, makers of our beloved boozy drinks have noticed this weird coating on their warehouses and distilleries. It was first reported in 1872 from distilleries in France, and a few years later it was determined that, although the coating looked like soot, this discoloration was actually caused by a fungus appropriately coined the whiskey fungus. And it’s quite widespread, thriving not only around distilleries in Europe but across North America too.
The whiskey fungus thrives on a particular ingredient from one of Humanity’s favorite vices—ethanol. It’s the active ingredient in all alcoholic beverages and is a byproduct of fermentation. Normally, when the kinds of yeasts that can ferment stuff are out and about, they’ll take sugars and break them down with the help of oxygen, which lets them make a whole bunch of energy. But if there’s no oxygen to be found, they have a backup mechanism called anaerobic respiration, and this makes energy for them too, but also creates ethanol.
Bad ethanol is pretty much the whole reason we make boozy beverages to begin with, since it produces a pleasant buzz—and occasionally an unpleasant morning after. But we’re oddballs, since very few other things in nature care about ethanol—it’s a byproduct, not the goal (at least from the fermenter’s point of view). They’re getting rid of ethanol, not seeking it out to consume.
So while it’s possible that whiskey fungus evolved to source its alcohol from fermenting fruit in nature, it hit the jackpot when a bunch of hairless apes started making this stuff by the barrel full, and we’ve gotten extremely good at making our barrel-aged drinks through the years. When distilled spirits are aged in wooden casks—a long-standing method that’s still used today—there’s a percentage of that ethanol that evaporates during storage, sometimes referred to as the “angel share”. This escaped ethanol can account for a two percent loss of the total volume of ethanol within these barrels every year. It’s the nature of the game, since that loss of volume is also what produces the richer flavors in your final aged product.
But that airborne ethanol can settle on the outside of the distillery walls, which lets the fungus get a consistent fix of their favorite alcohol. And as it turns out, whiskey fungus is shockingly good at using ethanol. Remember, to the things that make it, ethanol is straight up garbage—they aren’t able to use it for anything. So it’s surprising that the whiskey fungus seems to be totally fine getting energy from molecules that are otherwise considered waste products.
But when taking a deeper dive into the habits of this fungus in the early 2000s, researchers found that whiskey fungus doesn’t actually do so well in high concentrations of ethanol—like the humans that make it. Whiskey fungus has a limit on how much it can drink and still feel okay the next day, which is probably why it only grows on the outside of the distilleries. Everything in moderation, after all.
Whiskey fungus has developed a neat skill that lets it tolerate the stress of high heat and bright sunlight better than most other fungi. Various fungi are known to get through stressful environmental changes by increasing their production of trehalose, a type of sugar that protects their proteins from breaking down in specific situations like heat shock.