It was back in the late-1850s when Louis Pasteur became enamored with yeast. He wrote papers, identified the process of fermentation, and elucidated its behavior to the point of having a process named after him. He set the modern stage on which the beloved microbe performs. Before Pasteur, yeast toiled in obscurity even as it guided our evolution, built communities and wove itself into mythology and religion. For example, in the Christian bible, Jesus offers bread—albeit unleavened, perhaps not—and wine—definitely yeasty—at the last supper. Ralph Waldo Emerson gave a more Unitarian vantage by saying, “God made yeast, as well as dough, and loves fermentation just as dearly as he loves vegetation.” We’ve since identified over 1500 strains. The industry standard is S. cerevisiae, better known as brewer’s yeast, and is used in lagers and IPAs. Beer nerds will talk of “Belgian” and “saison,” less appreciated styles from even lesser known yeast strains. In the words of Twin Peaks fans, “What’s it all mean?” Meet Brettanomyces bruxellensis, a playful minx of a yeast, known to develop wildly unexpected results. It’s the scourge of some brewers for that very same reason. Lofty goals of consistency have to take a backseat when working with such yeasts. “I want the beer to taste good. I'm not super concerned about the beer tasting exactly the same every time,” says Brian Taylor, co-founder of Whiner Beer Co.

Flavor profiles developed with Brett can vary wildly beer-to-beer as well as brewery-to-brewery”

When I sat with Taylor at the Beer Temple, he was demonstrating two different Brett strains. Offering a side-by-side comparison of his beers named St Francis and St Francine. He explains, “The Brettanomyces family has a whole bunch of strains within in that family. What we do is add Lambicus to the Francis version and then we add Clauseneii to the Francine version. It's the exact same beer and you can see how different each one is.” Indeed, St Francis was fizzy on the tongue and tart. “So, Francis Lambicus, that's going to be more toward your real lambic style. It's a little bit on the cheesy side some would say,” according to Taylor. “That's the Brett Lambicus going to town.” St Francine was much more developed, though with only a slight effervescence, it had slick texture. It came across more like wine, perhaps a gewürztraminer. “Clauseneii is much softer, so you're going to get a little more well-rounded sourness,” Taylor explains. “It's not going to ‘punch you in the face.’” It also had a nice little pineapple character. “That's definitely part of the process with Clauseneii,” Taylor adds. Flavor profiles developed with Brett can vary wildly beer-to-beer as well as brewery-to-brewery. Just like Darwin’s finches, geography plays a role in yeast’s evolution. This is why beer, either made on Chicago’s Southside or in Europe, will taste markedly different.

Matthew Rogers, Good Beer Hunting

To corroborate this, I spoke with the affable Xavier Vanneste, CEO of the family-owned De Halve Maan brewery in Bruges, Belgium. His Straffe Hendrik unfiltered tripel “tastes different between 2014, 2015, 2016,” Vanneste affirmed. When the beer is bottled and shipped, it can still change. Vanneste explains that the Brett in the bottle is still living. “You have so much nest sugars still in a tripel, it's quite a challenge to keep it balanced,” he adds. As we drank, notes of honeysuckle, apricot, and even bubblegum cavorted with my senses. Vanneste discussed how volatile the yeast can be, all the while his cherubic face belied his seriousness. “If you let the same yeast ferment beer at 18 degrees or at 25 degrees (Celsius), you will have a completely different beer,” he continues. “And if you use this yeast 10 times again, you will have already some adaptations. We do genetic DNA test(ing) on our yeast." When it reaches a certain point of diversion, they go back to the original. Such variations occur in a tightly controlled environment. Things can go pear-shaped when the fermentation is left to nature. Thankfully, more and more brewers are facing up to this particular challenge. Enter the coolship. Hot wort (unfermented beer) is pumped into an open vessel to both be cooled down and exposed to the flora of its surroundings. The one used by the aforementioned Whiner pumps in air from the surrounding urban farm. “All that wild yeast and bacteria are going into the beer and they're fermenting the beer,” says Taylor. “You will not find that exact yeast and bacteria anywhere else in the world except in Bridgeport and the south side of Chicago. [The beer] cools down and inoculates itself so it spontaneously ferments. And then we send it into barrels and let it sit for two years.” This beer will be called Ghost Pig when Whiner decides it’s ready.

I say 'hats off' to those with the patience to work with this particular single-celled fungus.”