Along Kentucky's Bourbon Trail, a fungus known as "black velvet" has sparked bitter lawsuits.
The byproduct of the distilled drinks' aging process was discovered a decade ago by Canadian mycologist James Scott, who called it Baudoinia compniacensis in honor of pharmacist Antonin Baudoin, a Frenchman who probed a similar mold in the 1870s.
The "whiskey fungus" thrives in ethanol-rich environments, grows on roofing materials, exteriors of buildings and any surfaces that are exposed to direct sunlight, Scott told AFP.
To grow, it requires water and alcohol. The first comes from dew or humidity in the air while the second stems from the ethanol that evaporates as the spirit matures in oak barrels.
In a year or less, it can easily turn a white wall black. Left alone over the span of several years, that same surface will slowly become covered by a uniform crust.
George Boisvert, who lives near a Jim Beam production and bottling facility outside Frankfort, Kentucky, can attest to that only too well.
From his mailbox to rain gutters, the elderly man's house is speckled with the stuff.
"It's unsightly," he said as he scraped one of walls with a fingernail. "I don't want a black house, it's supposed to be tan."
Nearby, everything -- an old car, a jet ski stashed in a yard, wooden fences and dozens of other houses -- is veiled in the fungus.
Their owners all represent potential clients for William McMurry, a lawyer from Louisville, Kentucky, who has already recruited several residents for a lawsuit against five large bourbon and whiskey producers, including Jim Beam.
- Distilleries not 'good' neighbors -
The aim? Turning distilleries into good neighbors and having them install an ethanol capture system.
"If they're not a good neighbor, they need to be made responsible, personally accountable like the rest of us businesses," McMurry said.
"We don't want money lining in anyone's pockets. We're happy to walk away if they'll clean this house one more time and turn off the ethanol."
He spoke as three workers busied themselves cleaning a two-story house, half of which was still covered in gunk.
One of them spread a bleach-based product on the sullied surface, to be rinsed later under high pressure.
Mark West, the 45-year-old head of West Home Maintenance that charges $400 to $500 for a house cleaning, said he was pleased with business, which usually picks up in spring.
"I've lived in Frankfort since 1983, and since I've been here I can always remember this stuff getting on your cars and your house," he said.
"Everyone ... knows the distilleries are going to make your house dirty."
Still, it was not until 2006 that the first complaints surfaced in Louisville. Initially, authorities rejected or disregarded them.
But after Scott confirmed the fungus was indeed Baudoinia compniacensis, McMurry filed suit in 2012, first in Louisville and then in Frankfort.
He has also been contacted by a Scotsman on the matter.
- Nuisance or nice touch? -
A lawsuit against two famous distilleries, Brown-Forman and Heaven Hill, was dismissed in state court.
But two others are pending, one in state court against Buffalo Trace and Jim Beam and the other in federal court against British giant Diageo, owner of Johnny Walker whiskey and distributor of Hennessy cognac.
A trial could start two years from now, according to McMurry.
The distilleries reject the scientific arguments implicating them.
"We are taking this matter seriously and we are sympathetic to the concerns of the plaintiffs," said a joint statement from Diageo, Brown-Forman and Heaven Hill.
"However, the blackening of some buildings and other structures is due to naturally occurring mold that is found widely throughout the environment, including in areas unrelated to the production of whiskey."
Still, Diageo signed an agreement with Louisville's air pollution authority in July and agreed to close down a barrel-aging operation by the end of 2015.
However, it stressed that "the voluntary commitments ... do not constitute an admission of liability."
On the other side of the Atlantic, the legal spat elicited a smile from the mayor of Cognac, where walls have not been white for a long time.
"We've always said here in Cognac that you can tell the wealth of a house by the darkness of its tiles," Michel Gourinchas told AFP.
"Historically, this is what constitutes the wealth of the city, so we're not complaining," he added.
"The people of Kentucky should come here, we'll explain it to them!"