Cocktail Queries: What Exactly Is “Whiskey Fungus,” and Is It Dangerous?

Cocktail Queries is a Paste series that examines and answers basic, common questions that drinkers may have about mixed drinks, cocktails and spirits. Check out every entry in the series to date.

If you’ve ever gone on a tour of one of the major Kentucky bourbon distilleries, it’s a sight you’ve almost certainly witnessed–row after row of sky-high, wooden or tin warehouses (they’re called rickhouses in the industry), inside which one will find millions of barrels of whiskey statewide patiently aging. The numbers of barrels aging in these structures has skyrocketed in the last decade, as the whiskey industry has played catch-up to accelerate its production, years behind the curve of matching demand for many sought-after brands. This has meant the construction of many new rickhouses, an ongoing project that has in turn drawn attention to one of the industry’s less aesthetically pleasing sights: Whiskey fungus.

It’s another visual that you may very well have noticed while touring that big Kentucky bourbon producer: Rickhouses that are stained halfway up their sides (or entirely, in some cases) with a peculiar, black, grimy substance. Tour guides may have even pointed out why the rickhouses looked so strange or dirty, and the answer is all because of fungi. Specifically, the species that is generally referred to as simply “whiskey fungus,” which voraciously feeds and multiplies on a diet of alcohol fumes, which can obviously be found in abundance in the proximity of so many whiskey barrels. Rickhouses are the natural biome of whiskey fungus, and have been since at least the 1800s, when the species was first described. With the scientific name of B. compniacensis, the fungus was observed in France as early as 1872, blackening the walls of buildings near brandy distilleries. It has since been observed around the world, in Asia, Europe and the Americas–anywhere that barrels are left to age, leaking ethanol fumes into the air in the percentage of lost spirit over time that has classically been referred to as “the angel’s share.”

Historically, whiskey fungus has mostly been thought of as a rather innocuous eyesore. Most researchers say it’s not particularly destructive to structures or plant life, though it is extremely hardy, being able to grow in conditions of rapid temperature shifts that would kill most fungal species. It’s never been demonstrated to have any specific, adverse effect on human or animal life. Most people have never even seen whiskey fungus, except in the immediate vicinities of the rickhouses. But as the number of barrels aging in states such as Kentucky and Tennessee has continued to creep up, more small communities now find themselves being embroiled in bitter feuds over whiskey fungus, which has increasingly been characterized as an invading menace wreaking havoc on communities located near distillery property or warehouses.

A tree branch, coated in black whiskey fungus.

The most high profile of these fights has been ongoing for some time in Lincoln County, Tennessee, where the country’s largest producer of American whiskey, Brown-Forman’s Jack Daniel’s, has six barrel warehouses, with intent to build twice as many on another property. There, various residents have complained that the whiskey fungus has become a genuine problem, encrusting plants, trees, homes, cars and patios with sooty black particulate, allegedly fed by the alcohol fumes wafting from rickhouse sites. One resident took her complaints to the next level, suing the county in January, and claiming that the rickhouses near her wedding venue property lacked the necessary permits. In response, a judge recently halted construction on a new rickhouse, according to the New York Times. The resident, Christi Long, claimed her and her husband’s business had been damaged by the invasive fungus, which they attempted to remove every three months via pressure washing and bleach treatments. The fungus, she said, always returned.

“If you take your fingernail and run your fingernail down our tree branch, it will just coat the tip of your finger,” said resident Patrick Long to NYT. “It’s just disgusting.”

Whether or not the fungus is genuinely damaging to plants and property turns out to be a matter of some debate. A report from the Louisville Metro Air Pollution Control District in 2012 responded to similar concerns of property damage by seemingly concluding that the whiskey fungus was only really a threat in terms of “cosmetic” effects on local plants and property. On the other hand, professor James A. Scott of the Dalla Lana School of Public Health at the University of Toronto has studied the fungus since 2001, and told the New York Times that it was significantly bigger problem to deal with, saying the following:

“The fungus is pretty destructive, and the only way to stop it is to turn off its alcohol supply. It wrecks patio furniture, house siding, almost any outdoor surface. I’ve seen trees choked to death by it. It is a small mercy that it does not also appear to have a negative impact on human health.”

Jack Daniel’s and parent company Brown-Forman, meanwhile, have largely tried to stay above the fray, simply telling NYT that they “comply with all local, state, and federal regulations regarding the design, construction and permitting of our barrelhouses.” They’ve resisted calls to take steps such as adding air filtration systems to rickhouses, noting that the ability of outside air and the natural climate to enter in and out of barrels has myriad and subtle effects on the aging process and whiskey flavor. This is a valid point, as even the smallest changes to the production process could conceivably be capable of fundamentally altering the flavor off the company’s products as they age over the course of years. All in all, it leaves the fight at something of an impasse, with more potential litigation a possibility.

The delicious spirit within each barrel does come with a cost.

This isn’t a fight simply unfolding in Tennessee, however. Similar battles between small town or urban residents and local governments have been playing out in recent years in other states as well, from bourbon-producing powerhouses such as Kentucky, to small towns in Northern states one wouldn’t necessarily associate with large-scale whiskey production. Just this week, in the small town of York, Maine, south of Portland, an in-depth story in local media details the anxieties of local residents who fear that their own town will be encased in whiskey fungus, with an obvious effect on property values. Those residents are pointing fingers squarely at nearby microdistillers Wiggly Bridge Distillery, despite the fact that it’s a business with only around 1,000 total barrels of whiskey in a warehouse. It begs the question: What number of barrels is acceptable to not let the fungus proliferate outside of a rickhouse property, and what if anything should a distillery be expected to do to address the problem? That is, if it is indeed a problem.

We can take some comfort, at least, from the fact that even researchers like the above quoted James A. Scott seem to agree that the substance “does not appear to have a negative impact on human health.” The last thing we need is a malevolent strain of hardy fungus spreading from every one of our local whiskey producers, like some alternate origin story for The Last of Us. But given a whiskey market that shows no signs of slowing down, and with more barrels being set aside than ever, you might want to think twice before buying a property downwind from a rickhouse–lest you find out that you’re not the only ethanol-craving life form on your property.

Jim Vorel is a Paste staff writer and resident liquor geek. You can follow him on Twitter for more drink writing.