What Is Whiskey Fungus and Is it Dangerous?

Whiskey fungus grows up the outside walls of the Heaven Hill distillery in Bardstown, Kentucky. Wikimedia Commons (CC BY SA 3.0)

Key Takeaways

Whiskey fungus, scientifically known as Baudoinia compniacensis, thrives on the ethanol vapors released during the whiskey aging process, commonly referred to as the "angel's share."
This black fungus is not harmful like black mold (Stachybotrys) but can attach itself to various surfaces, including buildings, trees, cars and outdoor furnishings, causing aesthetic and potential property damage.
The fungus feeds on the sugar in the ethanol emissions, which can amount to 200 to 1,000 tons (181 to 907 metric tons) annually, depending on the distillery's production volume.

A lot of people like whiskey — especially Jack Daniels whiskey. According to data from Statista, the Jack Daniels straight American whiskey brand recorded sales of approximately 5.4 million 9-liter (2-gallon) cases in 2021. Considering that was during the second year of the COVID-19 pandemic, maybe the number isn't a surprise, but sales numbers have steadily climbed since 2013. Suffice to say, a lot of people like whiskey, and much of it is made at the Jack Daniels distillery in Moore County, Tennessee, which also has a thriving crop of a fungus familiar to anyone living near a distillery.

What Causes Whiskey Fungus?

Whiskey fungus — sometimes called distillery fungus, rum fungus or warehouse-staining fungus — is a black fungus with the scientific name Baudoinia compniacensis. Though the fungus is literally black in color, it is not the same as black mold, Stachybotrys, which can cause significant health issues and infrastructure damage.

Here's what happens: After whiskey is distilled it is held in barrels in a warehouse during its aging process. The length of distillation time varies but during the process, an estimated 2 to 5 percent of the alcohol evaporates. Depending on the amount of alcohol being processed, that can add up to as much as 200 to 1,000 tons (181 to 907 metric tons) of ethanol emissions each year.

The emissions are poetically referred to as the "angel's share" but there's evidence to suggest the vapors don't quite make it to heaven. When the ethanol combines with moisture in the air, the result is a type of fungus that feeds on the sugar in ethanol — whiskey fungus. Like any other fungus, it attaches itself to just about anything including buildings, trees, cars and outdoor furnishings.

What Gets Rid of Whiskey Fungus?

When distilled spirits like whiskey, Kentucky bourbon, Canadian whiskey or Caribbean rum are produced, distillery fungus appears. But it is possible to get rid of it temporarily. Some residents near the Jack Daniels distillery have pressure-washed the outside of their property with a mixture of water and bleach, only to have the fungus return a few months later. Beyond the obvious aesthetic issues, there are questions about the ongoing health and safety of a neighborhood shrouded in fungus.

Is Whiskey Fungus Dangerous?

Short answer: yes and no. Information from the Pediatric Environmental Health Specialty Unit (PEHSU) states that there is not a "sufficient body of evidence to state health risks associated with distillery fungus." However, PEHSU recommends wearing personal protective equipment such as N95 face masks, goggles and gloves if you plan to attempt removing the fungus from contaminated surfaces. Vulnerable populations such as children or people with health conditions — such as asthma or other breathing conditions — that might put them at risk should discuss possible concerns with their doctor. The group also suggests fully washing and removing visible contamination of "any produce visibly contaminated with distillery fungus." (Or maybe just throw those apples away.)

A Whiskey Fungus Fight Is Brewing

Homeowner George Boisvert shows the vinyl siding of his house, covered in whiskey fungus, in Frankfort, Kentucky. He has to pay a contractor to have the whole exterior of the house cleaned every few years. Ivan COURONNE/AFP/Getty Images

Some neighbors of the Jack Daniels distillery in Tennessee are up in arms because of the pervasiveness of the whiskey fungus. They'd like the distillery to install air filters in the distillery to limit the emissions and maybe even pony up for pressure washing in the neighborhood. One area resident is suing the county to try to stop the distillery from building additional barrelhouses. (She won a temporary injunction.) Other communities that have similar issues in Kentucky and elsewhere are watching the case closely.

A Jack Daniels official said the fungus doesn't damage property permanently since it's relatively easily washed off and it doesn't harm human health. They also declined to power wash the neighbor's property, citing liability issues. As for installing air filters? That's a definite no-go as they say it could impact the flavor of the whiskey.

However, according to one report, in California some distilleries and warehouses that age brandy have installed a system that collects the alcohol vapor and burns it off. Presumably this mitigation strategy would be extremely expensive to install, but it might be one solution that could bring the whiskey fungus war to a peaceful end.