Among the countless celebrities, marketing gurus and disenchanted journalists who claim ownership of various craft whiskey distilleries today, the duo behind Wilderness Trail stands out. Since launching in 2018, the brand has quietly become one of the best whiskey producers in the world, and many chalk up its success to the founders’ unique backgrounds.

“I had a very crooked path getting into distilling,” explains Pat Heist, who, along with Shane Baker, owns the Danville, Kentucky–based distillery. Heist had studied plant pathology in college, specializing in the diseases of field crops before becoming a professor of medical microbiology at Pikeville College. In 2006, he and Baker founded a company called FermSolutions, designed to supply yeast strains and fermentation products to breweries and distilleries.

Once that business was successful, garnering over 600 distillery and brewery clients, they turned their technical know-how toward creating their own whiskey. They selected a superior distiller’s yeast, one capable of finishing all available sugars and fermenting at high temperatures, culled from thousands of collected samples. Rather than the more common sour mash, they opted for a sweet mash fermentation, a riskier proposition due to the increased susceptibility of bacterial infestations. But Heist and Baker’s command of fermentation allowed them to navigate the risk, resulting in what many believe to be a more flavorful bourbon, even from an early age.

Today, Wilderness Trail is considered one of the trendiest distilleries in American whiskey, its private “picks” coveted, its barrels copped by crypto bros. You could say it’s all thanks to yeast. 

That wouldn’t seem like such a leap in other branches of the alcohol world, where yeast—whether the wild yeasts inherent to natural wine and spontaneously fermented lambic, or the “muck” that gives Jamaican rum its signature funk—is already fetishized, thought to be the source of unique flavors.

Yet, in the whiskey world, the barrel rules all. Yeast is barely considered aside from fanciful stories on distillery websites. “It’s another closely guarded family secret,” touts the Jim Beam website, “so guarded, in fact, that Jim Beam himself would take a jug of yeast home every weekend for safe keeping.” Indeed, most Scotch whisky distilleries have long relied on the same generic distiller’s yeast, letting the mash bill and barrel dictate the flavor of the liquid in the bottle.

“You go, ‘Wait a second, everybody uses the same M-1 strain,’” says Matt Hofmann, co-founder and master distiller at Westland Distillery, citing the ubiquitous distiller’s yeast. When he opened his facility in Seattle’s industrial SoDo neighborhood in 2010, he began thinking about how to coax as much flavor as possible out of malt whiskey’s three key ingredients: malted barley, water and yeast.

“Why is it that the craft breweries across the street from me are looking at yeast in a different way?” he asked himself. Living in a notable hotbed of brewing in the Pacific Northwest, Hofmann soon discovered that his dark roasted malts, with their pastry and chocolate notes, worked particularly well with the fruity notes imparted by Belgian saison yeast. “You can definitely taste the impact of yeast,” he says. He settled on a strain called T-58, and he’s used it in every whiskey he’s made since. 

This craft beer–like reverence for yeast has taken hold at other distilleries, too. At Leopold Bros. in Denver—founded by two siblings who formerly ran a brewery in Ann Arbor, Michigan—wooden fermentation tanks made of Oregon pine are positioned adjacent to open windows that have been fitted with a system that pulls outdoor air in, intentionally inoculating the mash with the bacteria and wild yeast from their fruit and herb garden just outside. It’s a system not much different than the legendary koelschips of Cantillon and 3 Fonteinen, the superstars of Belgian lambic.

“All of this stuff we’re doing is trying to get a house note,” Todd Leopold told American Whiskey last year, claiming that octyl acetate, an ester formed from organic compounds often found on citrus fruit, in particular gives his distillate hints of orange marmalade.

Distilleries like Chattanooga Whiskey, James E. Pepper and New Riff have gone so far as to hire brewers to work as distillers. Before becoming New Riff’s founding distiller in 2014, for example, Brian Sprance had been a brewing supervisor at the nearby Cincinnati outpost of Boston Beer Co. (aka Samuel Adams), where he was making around 80 different beers per year. At New Riff, he also uses open-fermentation methods and the “hungriest” dry yeast he could source, that is, a strain that excels at converting sugars to alcohol.

“I think some of the best distillate we’ve made, I’d compare to a funky saison,” says Sprance, echoing Hofmann. “I’m trying to get as many esters out of this yeast as I can so that when I distill I can bring all those flavors forward.”         

Even as whiskey distillers embrace the different flavor profiles created by yeast, only one major Kentucky distillery truly touts that difference: Four Roses. The Lawrenceburg distillery utilizes five proprietary yeast strains drawn from Seagram’s yeast library of around 3,500 strains (acquired when Seagram still owned Four Roses as far back as 1946), each denoted by a different letter—F, K, O, Q and V—which are highlighted on all single-barrel and small-batch releases. (They also use two different mashbills, B and E). While the standard Four Roses Single Barrel bottling always uses V yeast, said to taste of “delicate fruit,” the more limited releases are composed of blends featuring multiple yeasts that die-hard fans are known to try and replicate.

It remains to be seen whether Kentucky’s dozens of other major whiskey distilleries will ever follow suit, but with more than 1,000 whiskey producers now in America, yeast remains one of the few untapped angles for differentiating one’s products. Who knows, as the practice picks up steam, once-obscure yeast strains might become as trendy as toasted-barrel finishes or double-oaked releases. But for now, it remains as unexplored as the deep ocean. Says Hofmann: “It’s not talked about a lot, but the possibilities are endless.”