Black Fungus Fed by Whiskey Fumes Spreads Near Ireland's Distilleries

A black fungus is spreading on walls, roofs, road signs and trees near whiskey warehouses in Ireland, fed by ethanol vapor escaping from the maturing spirit. The fungus, called Baudoinia and known as "whiskey fungus" or "whiskey black," has been documented around spirit maturation warehouses for more than a century, first around cognac facilities in France and later in Scotland, Canada and the United States.

During maturation, ethanol and other volatile compounds evaporate through the porous wooden casks — a loss distillers call the "angels' share." A review for the Scottish government estimated that more than 90% of non-methane volatile organic compound (NMVOC) emissions from whiskey production occur during maturation, with ethanol dominating. Baudoinia occurs naturally at very low levels but grows more where it is exposed to this airborne ethanol, producing the dark patches seen near warehouses.

Irish whiskey exports were worth more than €930 million in 2025, and exports to the EU have grown by more than 21% over four years. In 2022, after a complaint about black discoloration on houses near the Midleton distillery in County Cork, Ireland's Environmental Protection Agency (EPA) checked for Baudoinia. The fungus was found on a whiskey warehouse but was not detected on any of three nearby homes sampled.

A recent review led by University College Cork researchers suggests ethanol may act as both a germination signal and a carbon source for the fungus, and that visible colonization depends on distance from the source, wind, moisture, and the surface involved. These NMVOCs can also form ground-level ozone, a pollutant that damages vegetation and crops, reduces lung function, and worsens asthma, and act as a greenhouse gas. Ireland has committed to cutting NMVOC emissions under an EU directive.

A Scottish government review found no evidence of health effects from exposure to Baudoinia, though it flagged evidence gaps and urged further study. Researchers at Dublin City University, with the University of Toronto, have started an EPA-funded project called EREG combining emissions estimation, monitoring and microbiology to study Irish ethanol emissions and how Baudoinia spreads and is regulated.