It’s called Yowza! and, for the last 13 years, it’s lived inside a small keg not far from wherever brewer Bob Kunz works.
Yowza! is a custom cultivated yeast that started as a homebrewing experiment. Kunz would take the dregs from bottles of beer he’d enjoyed, mostly Belgian, and would propagate the microbes to make his own brews.
Over time, new strains were added to accentuate attributes that appealed to Kunz, the owner/brewer of Highland Park Brewing in Los Angeles. Ambient yeast also settled into the slurry over time. Eventually, the combination became a certified house culture, specific to the brewery and nearly impossible to replicate.
“It is our history and environment in microbiology form,” says Kunz.
However, yeast changes from location to location. Brewers that experiment with wild or sour beers often cultivate their own yeasts that are both site-specific and uniquely flavored. An identifiable house culture, they say, is like tasting a brewery’s DNA.
“A house culture is a magical thing of value that no one else can have.” —Jeff Mello, owner, Bootleg Biology
Although certain producers pride themselves on custom wild fermentations, the majority of the country’s roughly 8,000 breweries use yeast pitches that include strains of Brettanomyces, ordered from laboratories across the U.S.
“Brewers have access to all of the same clean and cataloged strains,” says Jeff Mello, owner of Bootleg Biology, a yeast lab in Nashville. “A house culture is a magical thing of value that no one else can have. It’s unique to them and cannot be recreated by someone else.”
Mello stores samples of house cultures from breweries across the country. If a brewer needs a fresh pitch, especially if the current generation of yeast no longer resembles its former self, they contact Mello.
When beer professionals talk about house cultures, they often mention Belgian lambics. These celebrated beers by breweries like Drie Fonteinen and Cantillon have distinct flavors, thanks to microbes developed over the decades that live in the eves and other surfaces of the breweries. These house cultures also inoculate the wort, housed in open vessels like coolships, to begin fermentation.
In late 2014, Jean Van Roy, owner of Cantillon, said that as his operation grew, he took on new warehouse space to age barrels. He was so intent on giving those barrels that same ambiance as the brewery that he sprayed the warehouse walls with Cantillon beers to introduce the house yeast to the structure.
Unique house cultures can start with another brewer’s yeast, or they can be pulled from the air around a brewery, even from plants. From there, brewers nurture and cultivate them with nutrients and keep them stored in ideal conditions.
Some cultures have high acidity and citrus aromas, while others have funky, earthy scents. Brettanomyces is often present, and it provides an array of flavors including leather, pepper and stone fruits.
“I’ve had several people who are big sour beer fans says they can tell when they are drinking our beer blind that it’s ours,” says Levi Fried, co-owner of Long Beach Beer Lab in California. The brewery uses sourdough yeast co-owner Harmony Sage hand-mixes daily at her bakery.
“This is truly unique to us and only we can make this beer,” he says. “It’s an extension of ourselves.” Among the pronounced flavors that its house yeast produces is an aged Sherry note.
A brewery is not limited to just one unique house culture, either.
Jeremy Inzer, head brewer at Fonta Flora Brewery in Morgantown, North Carolina, says the brewery maintains three strains, two which are banked at Bootleg Biology for safe keeping.
The first culture was created by brewery owner Todd Boera, who pulled yeast samples from other breweries’ bottles during his days as a homebrewer. Another, “Dandy,” is made from microbes stripped off dandelions. The most recent culture came from a coolship beer that the brewery made on its farm in Nebo, North Carolina.
“It has this light fruity note like peach and mango,” says Inzer. “It’s all yeast-derived, and we’ve even thought that sometimes the flavors were too pronounced, so we had to up the hop dosage a bit to keep it at bay.”
Unlike yeast from a catalog that, if used correctly and in the same way batch after batch, will produce the same results, there’s always a bit of uncertainty with a house culture. For Mello, that’s part of the appeal.
“You’re never going to fully control it, and that’s the thrill of house a house culture,” he says. “There’s a variability, and you know that you won’t have 100% repeatability.”