It’s not heavenly creatures, but a sooty black fungus that thrives on pollution produced in alcohol distilling processes. Now, Louisville distillers face growing pressure to curb the ethanol emissions that drive the spread of this “whiskey fungus.”

The fungus Baudoinia compniacensis grows in what is known amongst distillers as the angel’s share: ethanol vapors that escape the oak barrels during the aging process. The vapors allow this stubborn fungus to grow everywhere: sidings, plants, outdoor furniture, even toys left outside.

Each bourbon barrel loses about 2% of its liquid per year of aging, adding up to 2000 tons of ethanol released into the air by each of three large distilleries with maturation warehouses in Louisville: Heaven Hill, Brown-Forman, and Diageo—who market such brands as Elijah Craig, Jack Daniel’s, and Bushmills.

Some companies, such as E & J Gallo, a winery and brandy maker in California, have found a solution to eliminate their ethanol emissions in order to meet local air quality regulations. A machine called a Regenerative Thermal Oxidizer sits outside the warehouse, where it powers itself with half the vapors it collects, then burns the other half, converting it to carbon dioxide and water vapor.

Though the Louisville distillers claim that these measures would destroy the flavor of Kentucky’s iconic bourbons, Gallo has noticed no change in the character of their brandy after years of using the machine.

There are, however, some possible benefits from the fungus – when it grows in the right places. B. compniacensis, along with another cellar fungus, has been found growing on old whiskey barrels. Brett Porter, a brewmaster at Goose Island Beer Co., noticed this on some bourbon barrels from Heaven Hill that came to him for aging the brewery’s Bourbon County Stout.

For the regular batch of this stout, the brewery blends all the barrels together after aging to get a consistent flavor. But when Porter sampled just the stout from the fungus covered barrels, he found that it was smoother and the flavors were easier to pick out: chocolate, cherry, oak.

He picked out the funkiest barrels of the bunch, and poured a special batch of “Baudoinia Bourbon County Stout” last winter in Chicago (it went over quite well). Now he’s waiting on the results from one barrel he set aside for a cuvée,. It’s sitting on the floor of his own aging warehouse as Kentucky continues their attempt to clear the air.