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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.

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Since the early days of distilling, makers of our beloved boozy drinks have noticed this weird, sooty 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. See, normally, when the kind 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 not oxygen to be found, they have a backup mechanism called "anaerobic respiration," and this makes energy for them, too, but also creates ethanol. That 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 what whisky 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's share," this escaped ethanol can account for a 2% 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 who 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.

And 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. And it looks like the whiskey fungus is doing that, too.

Low levels of ethanol not only stimulate its growth, but also make the fungus produce more trehalose, which means the sun-exposed whiskey facility walls aren't a roadblock for this fungus, even when it would otherwise probably prefer something a little more humid and dank. So, although a sunny surface would be a nightmare scenario for most fungi, by doubling down on stabilizing its proteins and membranes, the whiskey fungus makes itself extremely resilient in otherwise inhospitable situations.

Since it's mainly been found growing on the outside of distilleries, for the most part, people haven't been particularly concerned about its presence. In France, it was even considered a traditional part of the production process. That is, until folks took notice of its spread well beyond distillery walls. This pesky fungus not only covers warehouse walls, but also any fences, trees, cement - basically everything outside and within reach of the boozy vapors, which has become more of a problem when distillers try to build their warehouses too close to neighborhoods or towns.

Several communities have complained about nearby whiskey-making facilities, and some have even filed lawsuits against the distillers. So there's more pressure to curb the appetite of the whiskey fungus. One solution is to just make sure that the distilleries take more precautions with air filtration to keep the "angel's share" from spreading all over the place. But distillers aren't fans of that idea, as they worry it will change the flavor of their aged alcohols. And even if they were able to curb most of the escaped ethanol, tiny quantities still might be enough for the fungus to thrive. There's also a thought that, although it might seem counterintuitive, more ethanol exposure could actually help solve the problem, since we do know that too much of a good thing *does* stop this fungus' growth. For now, it seems that the best approach is frequent and heavy-duty cleaning. So if you live near a distillery, it might be time to invest in a power washer?

We still don't know exactly what the best solution is for keeping this sooty-looking fungus at bay, but in any case, it might be time to rebrand the "angel's share" as the "fungal share" in recognition of the alcohol-loving sunbather that's creeping out of distilleries and into the wide world.

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