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The Controversial Reason Why Everything Is Black Near Distilleries

Last Updated: April 18, 2023

Why Does Everything Turn Black Around a Distillery?

The black staining common at some distilleries is not caused by soot but by a sooty mould named Baudoinia compniacensis, also known as the Whisky Fungus. Rickhouses / warehouses will likely see the most significant accumulation of Baudoinia as they are the primary source of ethanol vapour release at a distillery. Baudoinia thrives in the presence of ethanol vapour.

view between two stone warehouses at Blair Athol distillery

Blair Athol Distillery Warehouses With Staining - Ing, Mcdonald and Taylor reported Baudoinia on the walls, birch and cherry trees in 2018. Photo taken by Amanda Reid in 2017.

Why Whisky Warehouses/Rickhouses are the Main Source of Baudoinia

Whisky fungus thrives on the 'angel's share', or the ethanol released from maturing barrels of alcohol spirit (whisky, whiskey, brandy, rum). Barrels and casks are made of timber, which is naturally porous, and as the seasons change and the temperatures and humidity in the warehouses fluctuate, the timbers of the barrels expand and contract. The expansion and contraction help to flavour the whisky (as it soaks into and is squeezed out again from the wood). It also results in some of the maturing spirit (ethanol and water) evaporating over time (anywhere from 2% to 12% per year, depending on the climate).

Baudoinia may not be present at a distillery if their casks are matured off-site, as the still house is not the primary source of environmental ethanol. As Bruce Ing, Murdo Macdonald and Stewart Taylor note, "crucially, the presence of a maturation warehouse determines whether the fungus will thrive: Teaninich in Easter Ross, without such a store, is clean, while the nearby Dalmore, with a store, is affected."

Falkirk Council in Scotland, which hasn't had an active distillery in the area since Rosebank closed in 1993, has been the site of at least two lawsuits (2009 and 2019) as Diageo's central warehouses are there.

heaven hill warehouses bardstown kentucky showing Baudoinia compniacensis growing on the base of the buildings

Heaven Hill Distillery Warehouses at Bardstown, KY on October 13, 2012. The black fungus growing at the base of the buildings is Baudoinia compniacensis, a natural result of the maturing process. — Photo by volgariver via DepositPhotos

What is Whisky Fungus?

A "veritable scourge" that "invades the tiles of the roofs and covers the walls with a blackish coating" was identified in the Cognac region of France by Antonin Baudoin (approx. 1872), a pharmacist and director of the French Distillers’ Association. Examination of Baudoin's samples was conducted by Casimir Roumeguère and Michel Charles Durrieu de Maisonneuve who named it Xenodochus baudoin, however their results were unpublished at the time. Further investigations were undertaken in 1881 by Misters Richon and Petit, who proposed the name "Torula Compniacensis (from the Latin name of the town of Cognac), very close to Torula conglutinata Cord. also because of its chagrined or tuberculous spores" [long elongated tubes, see images below].

Antonin Baudoin had noted (via Roumeguère's account) that "the owners of the cellars where the spirits are kept are obliged to clean them frequently; it is a veritable scourge". It was mostly a problem confined to Cognac as it "is disappearing in Aunis and it would not be found in the vicinity of the distilleries of the south of France". [translation of the original text via google translate].

Uploaded a work by Doctor Richon M.M. from Richon MM, Petit P (1881) Note sur la plante cryptogame des murs de Cognac ( Torula compnia- censis sp. n.). Brebissonia 3(8):113–116

Torula compniacensis illustrated by Richon, Charles Édouard, 1820-1893, Public domain, via Wikimedia Commons.

James Scott et al (2016) report:

"although associated only with industrial pollution, Baudoinia probably exists in nature as isolated microcolonies where its growth may be favoured by the presence of natural ethanol emissions associated with decomposition or in microenvironments where it is not subject to competition from other microbes. Its conidia (modified cells) probably break free from these microcolonies, becoming distributed in the air, although it is not a common airborne fungus even in areas with extensive Baudoinia growth (J.A. Scott, unpubl.). Baudoinia is also present on used whisky barrels (Scott et al. 2007) suggesting that the transport of whisky barrels provides inoculum to seed its establishment in new habitats. However, it is only in the presence of the unnatural, superfluous ethanol emissions of industry that these fungi grow luxuriantly, producing thick, confluent, crust-like colonies indiscriminately on nearly every surface, causing extensive aesthetic damage."

In the same report (2016), Scott et al examined "19 strains recovered from environmental samples near industrial settings in North America, South America, the Caribbean, Europe and the Far East" and identified from gene sequencing five geographically distinct species: Baudoinia
(Caribbean), Baudoinia caledoniensis (Scotland), Baudoinia compniacensis (the original, Cognac, France), Baudoinia orientalis (Korea), and Baudoinia panamericana (the Americas).

figure 3 from Scott et al 2016 showing cultures of Baudoinia and contrast microscopy photographic images

Source: Scott et al 2016. Figure 3. a. Scrapings from mortar joint collected at a spirit aging warehouse in Kilmalid, Dumbarton, Scotland (parent specimen of B. caledoniensis, UAMH 11554) cultured on EBM at 26 °C for 18 d; b. enlargement of 5 × 5 mm square elaborated from (a) showing developing microcolonies of B. caledoniensis (e.g., inset square); c. enlargement of 500 × 500 μm square elaborated from (b) depicting microcolony of B. caledoniensis; d. pure culture of B. panamericana (UAMH 10764) on MLA from a streaked spore suspension incubated at 26 °C for 28 d; e–h. colonies of Baudoinia species photographed in Nomarski Differential Interference Contrast microscopy from slide cultures grown on MLA; e. Baudoinia caledoniensis (UAMH 10761 T); f. Baudoinia compniacensis (UAMH 10808 T); g. Baudoinia orientalis (UAMH 10814 T); h. Baudoinia panamericana (UAMH 10809). — Scale bar = 10 μm.

Ing, Macdonald and Stewart propose a likely reason for why Baudoinia wasn't present in Scotland until the 1980s.

"In past centuries Scotch whisky was matured in oak casks made by local coopers...and later in imported sherry casks. As the original site for our fungus was Cognac it may be that old brandy casks may be significant in the story."

Baudoinia was present in Cognac as early as 1872. The various whisky industries probably only acquired Baudoinia once they started repurposing ex-Cognac casks. While bourbon must be aged only in a new, charred oak barrel - a minimum of 2 years for straight bourbon - once it's done its time and is of age, it can be 'furthered' in other barrels, such as ex-Cognac casks. A bourbon distillery may have traditionally only had new oak casks on site (which probably didn't have Baudoinia), but once they brought Cognac casks in, they also brought in Baudoinia. A similar introduction would have occurred in Scotland. Scotch distilleries use a lot of ex-bourbon casks, sometimes ex-Cognac casks, and sometimes barrels from other Scottish distilleries - barrels are shipped from one distillery or country or continent to another, readily transporting the microbes and spores that reside on or in the timbers.

Glenfarclas Distillery Warehouses - Ing, Macdonald and Taylor reported Baudoinia on walls and signs at Glenfarclas in 2018. You can see black staining of the walls here, especially around the door far left - photo taken by Amanda Reid in 2017.

Why are trees (posts, houses) black around a distillery?

In a 2007 report, Scott et al. noted that they rarely found Baudoinia in "spore-trap air sampling from regions where heavy colonization was observed on building exteriors". They suggested that this "implies other modes of dispersal, such as rain splash or invertebrate-mediated dissemination". They noted the presence of what looked like mollusc (snail/slug) trails through the Baudoinia colonies.

How Baudoinia spreads from warehouses and gets on everything in the neighbouring area is still a mystery. As Baudoinia is generally not found in air samples even when Baudoinia is in high concentrations, it probably isn't simply carried around on the breeze. Baudoinia is most likely transmitted by insects and/or slugs and snails, though this is still just a hypothesis.

That it does spread and infest the neighbouring areas is evident, though.

Wired Magazine reported in 2011 that Scott first encountered the whisky fungus in 2007 when commissioned by Hiram Walker Distillery's Director of Research, David Doyle, to investigate a mysterious fungus in Lakeshore, Canada, where the distillery ages barrels of Canadian Club whiskey. "In the neighborhood surrounding his Lakeshore warehouses, homeowners were complaining about a mysterious black mold coating their houses"... "the distillery had been trying to solve the mystery for more than a decade".

"In Lakeshore, Scott found the black fungus as far as a mile away from the warehouse. And the closer it was, the thicker it grew, clinging like ashy cotton candy to walls, rooftops, even garden furniture."

Baudoinia is almost impossible to get rid of as long as there is ethanol present for it to feed off, as it will simply grow back after it is removed and it will grow on almost any surface. The only substrates it doesn't like to grow is on are copper and galvanised steel, though it will happily grow on stainless steel. Scott et al reported in 2007 that:

In addition to ambient ethanol, B.compniacensis favors surfaces that are subjected to great environmental exposure, such as building exteriors and roofing materials that experience extreme diurnal fluctuations in ambient conditions. In parts of North America, the peak daytime temperatures of asphalt, roofing shingles with full sun exposure during the summer can exceed 65 C, while nighttime surface temperatures fall to as low as 15 C 

Baudoinia is incredibly heat tolerant and will also withstand high concentrations of salt.

The Cost of Baudoinia

Warehouse staining wouldn't be an issue if it just stuck to the warehouses. 

In 2009 BBC Scotland reported on a lawsuit raised by residents living in Bonnybridge, near distillery giant Diageo's Falkirk warehouses. The BBC stated that

"An MSP is calling on a council to take legal action against a drinks firm after black mould covered new homes built near a whisky storage facility. Michael Matheson said the lives of Bonnybridge residents had been made a misery by the mould which formed on homes close to Diageo's warehouse. He wants Falkirk Council to sue Diageo under the Environmental Health Act. Diageo and Health Protection Scotland said no direct link between the mould and the firm's operation was known."

In 2017, the Scotsman reported that a Bonnybridge couple "Thomas and Gail Chalmers want drinks giant Diageo to install “abatement technology” as they claim their home in Bonnybridge, Stirlingshire, has been stained black by the Baudoinia compniacensis fungus, a by-product of the whisky maturation ­process. The couple’s home is near warehouses belonging to the firm." 

In 2019 proceedings continued (as reported by the BBC) and the Chalmers were suing Diageo for £40,000 as

“the value of their house has been reduced by between 5 and 10% because of the effects of the fungus on properties. They also said their cars were affected by the fungus. Diageo claims that the blackening complained of does not cause serious disturbance, substantial inconvenience or material damage and property values are not affected. The firm previously tried to have the claim dismissed but a judge rejected the move and a second bid to get the case thrown out has been rejected. It will now go to an evidential hearing."

In their report The Fungus that Likes Scotch Whisky, Ing, Macdonald and Taylor, note that

"Falkirk Council commissioned an investigation into the problem. The resulting report must be rejected for a number of reasons. The introductory material on ‘moulds and fungi’ is out of date and full of inaccuracies. The report relies heavily on a paper by Watson, Minter and McKelvie et al.
(1984) which listed eleven species found on distillery warehouse walls. Only one is a sooty mould. Not surprisingly Baudoinia is not included
in that paper, even as Torula, as it had not been recognised in the United Kingdom, and may not have been here then, and, of course, the new genus had not been published. For the Falkirk study a number of sites in the Bonnybridge area were examined and several, but not all, of the species in the 1984 paper were found. However, the study failed to mention the existence, let alone the presence, of Baudoinia, which suggests
that its authors did not know of the species and its history. In these circumstances the distillery company can hardly be blamed for denying the
presence of Baudoinia. Unfortunately our own study found it on trees near the distillery."

For a more detailed breakdown of the different legal cases/implications in Scotland, see Physiological Effect of Saltwater on the Warehouse-Staining "Whisky Fungus", Baudoinia.

In March 2023, a Tennessee court blocked the construction of new Jack Daniel’s warehouses after neighbouring residents filed lawsuits against Lincoln County. The residents are “concerned about the amount of ethanol in the air that's feeding the fungus and worry about it causing lung cancer”. Jack Daniel’s were in the process of building an additional 14 warehouse in the area. The residents are requesting that Jack Daniel's install air filtration systems on the warehouses. Moore County News reported that while Jack Daniel's are not against filtration, "when you look at rules and regulations and the findings, the type of [filtration] technology available is not applicable at this time to what Jack Daniel’s is doing".

As reported by “Kentucky homeowners filed class-action lawsuits against several Louisville distilleries in 2012, though they were eventually dismissed". Diageo was one of the distilleries sued by Kentucky residents in 2012. There was an additional lawsuit against Diageo in 2015.

As of 2023, there do not appear to be any studies completed or ongoing into how Baudoinia affects human health. However, the other health factor needing investigation is whether there are ill effects from humans inhaling the ethanol vapour Baudoinia is thriving on.

Edradour Distillery: Ing found Baudoinia on trees at Edradour in 2018. Photo taken by Amanda Reid in 2017.

What is the black stuff in my whiskey?

Don't worry, it's not fungus! The inside of whisky barrels (especially bourbon barrels as they're charred) often breaks down over time, and pieces of cask or charcoal end up in the liquid. Most distilleries will filter their whisky to one degree or another before bottling. Some will only filter enough to remove solids, while others will go as far as to remove oils that might cause the whisky to go cloudy at cooler temperatures (a process called chill-filtration or chill-filtering). Some distilleries won't use filtration at all, so you may sometimes see 'bits' in the bottle or in your glass.

References and Further Reading

About the author


Amanda is an Australian-born photographer, digital nomad and whisky lover. Her passion for travel and whisky lead her to Islay, where she fell in love with an Ileach (an Islay native). Amanda and Roddy now share their Spirited Adventures.

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