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Meet the "Yeast Hoarder" Changing the Face of Sour Beer

Ehren Schmidt's Copenhagen brewing lab is a small-scale seed vault for beer yeast.
All photos by the author. 

"Yeast hoarder." This is how Ehren Schmidt describes himself. It might sound like a vicious nickname dished out by schoolyard bullies, but the brewer wears it as a badge of honor. Schmidt, sporting a freewheeling beard and hair tied into a bun, is standing on the steel platform that constitutes his brewing lab in Copenhagen’s Refshaleøen. He opens a small fridge and reveals shelves neatly organized with petri dishes, like a small-scale seed vault for beer yeast.


If you want to understand what makes the 32-year-old tick, the secret lies in this fridge. Schmidt is head brewer and master blender at Baghaven, which is a Mikkeller-owned tasting room and brewery located in an old shipyard warehouse on the waterfront of the Refshaleøen island.

Forget about sticky coffee-flavored stouts or heavily hopped IPAs; Baghaven is all about ‘farmhouse saisons’, fresh, sour, dry, and barrel-aged to develop distinct flavors. And relying on the magic of microbes.

“We are making Belgian and American wild ales, which means we use wild yeast, not conventional brewer’s yeast,” Schmidt explains. “We use a lot of different microbes that are not commercially available, we isolate them and implement them into the beer ourselves. What I do day in and day out is to taste these barrels, blend in yeast, look for new yeast types. This is the only style of beer we are focused on producing. We are not distracted by anything else.”

It was the blend of science and brewing that initially got Schmidt hooked on sour ales. He grew up in St. Louis and studied geology and microbiology at the University of Missouri. While he was in school, his student budget didn’t allow him the luxury of drinking the import beer that he craved, so he turned to homebrewing. After college, he ditched the conventional career path of a geology graduate—working in the oil industry—and instead pursued a career in brewing. It led him to San Diego and the brewery Toolbox, which specializes in mixed fermentation beers using wild yeast.


"I wanted to make beer like this—wild ales—because I thought it was challenging,” says Schmidt. “This style of making beer meant that I could be a brewer, which is an art, and a fermentation expert, which is a science, and combine the two. I missed science."

When Schmidt was offered the full-time job as head of Baghaven’s brewery, he wasn’t able to leave all of San Diego behind. Or at least not all of its potent yeast. When he checked in at San Diego International airport in July 2017 for his Copenhagen-bound flight, his bag contained a special stash: he brought 20 sterile tubes containing small liquid samples of wild yeast strains captured in the San Diego area.

“I had an insulated bag, like the ones from the grocery store you use for carrying frozen food, and I put the vials in there with frozen ice packs. Then I put it into my bag next to my shoes, underwear and my socks.”

In Copenhagen, he uses the imported strains for some of the Baghaven saison beer, but he’s impressed by the yeast hoarding potential on the old industrial island in Copenhagen.

“We are having a heyday in here in Denmark when it comes to capturing wild yeast,” he says. “Yeast is naturally found, but it needs a food source so that typically means tree sap, flowers, fruit skins. Anywhere you can eat sugar to survive, and here I’ve found rich biodiversity.”

Outside the Baghaven bottling facility, next door to where a new food market is opening later this summer, Schmidt is going hunting for yeast. Wearing thin lab gloves, he picks tiny dried blackberries off a bush. On the other side of the building, he uses a sterile tube to scrape shavings of bark from an old apple tree that’s nestled in between an old graffiti-covered container and a yellow taxi boat docked on the quay. “ This,” he says, looking around the harborfront,” is the wild west of Copenhagen."


Those little samples—a crumbled blackberry or a small sliver of sap-spiked bark—could be the start of the next Baghaven beer. After sourcing a potential source of wild yeast from a tree or bush, he adds sterile wort to see how any potential bacteria or yeast develops. Once they isolate a yeast strain in the lab, and identify its DNA, Schmidt uses wort to ferment the bacteria and expand the volume so there is enough yeast to add to the beer which he ages in old chardonnay barrels stacked around around Baghaven’s cavernous warehouse.

That doesn’t mean that one yeast strains equals one type of beer. "We are always experimenting here,” he says. ”I can put a new strain in one of our barrels—we have about 120 barrels here and 12 large foeders—and if it's not perfect then I can blend it with 20 other barrels, and it might contribute one component to a flavor wheel. To me, brewing is obviously about making the wort—which I do myself too and that’s important - but it's the fermentation, the aging, all the other techniques that we do here that make the beer unique."

Baghaven beers age in barrel or steel tanks for a few months or up to a couple of years, and they go through another round of fermentation once they are bottled. Some of the beers are mashed with fruits or berries before they are bottled, like the beer Stevnsbær, named after cherries from the Danish winery Frederiksdal.

Schmidt was blown away when he first tasted the cherries: "They were sour, quite tannic, and so full of rich cherry flavour. You didn’t get that marzipan character at first, because you are not eating the pit, but that really translated after the brewing.”


He pours a glass of Stevnsbær, holding the short-stemmed glass up to the light to illuminate the ruby-red hue of the cherry-spiked beer. He dips his nose toward the glass. “There is wood and oak and dried fruity hay, but then you get this smack of cherry and almonds, all this cinnamony funkiness.”

You don’t rank your children, but it’s hard to contain Schmidt's excitement for the beer “Gift from Demeter,” a spelt saison fermented with a mixed bag of yeast hailing from as far away as Belgium, San Diego, and Refshaleøen. A truly global soup of quality yeast. The beer is frothy and sparkling, almost like a sorbet. “On the palate it’s really dry, lemony, tart but not sour. Our saisons are getting a house character, which is this lemony dryness. That distinct character is important. It’s not complicated beer: just fermentation, barrel aging and a little bit of time.”

Actually, quite a lot of time. What is it like to produce beers that—in most cases—you won’t be able to taste the full rewards of until months or even years later?

"You can watch the beer evolve and it's really fun seeing it go from something quite simple into a complex product. When you start out, you can't wait to taste the first drop, but you kind of get used to that feeling. And when it’s ready, it probably never went 100% like you imagined."

“It's wild, isn't it?”