Some yeast samples in the Mellos' freezer.
Some yeast samples in the Mellos' freezer.

The Untapped Potential of Beer’s Most Underappreciated Ingredient

Most brewers use only a handful of commercial yeast strains. What a waste.


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When talking beer, I go on about hop varieties, brewing styles, types of malt, and specific gravity. And while I may call a beer “yeasty,” I rarely take the topic further than that.

My lack of yeast knowledge is pathetic, considering fermentation literally cannot happen without the single-celled organisms. But even when it comes to the most interesting craft beer, there’s not much interesting to say in the way of yeast—most brewers use the same few commercially available strains. “A study in the journal Cell last year found that most commercial yeasts could be genetically traced back to two or three domestication events,” says Ronn Friedlander, a microbiologist turned brewer at the Boston-area Aeronaut Brewing. In other words, even the most creative brewers are using yeast that’s genetically pretty darn similar to that of their competitors, including the big guys like Coors.

But we live in a big, wide, yeasty world, and some brewers can’t help but wonder: Is there more out there? Absolutely, says Jeff Mello, who, along with his wife, co-founded Bootleg Biology, an open-sourced yeast collection project. The idea struck after brewing a beer with wild yeast from his backyard in 2013. Now the couple collect and bank samples of yeast from all over the country, using sterile petri dishes and a smear of agar gel to feed whatever they swab from flowers, fruits, or even the bark of fallen trees. Their goal is to fill a freezer with one strain from every zip code in the United States.

“Some people say that as much as 70 percent of the flavor in a beer is from yeast, although I think that depends on the type of beer,” says Friedlander. Belgian ales and German wheat beers, for example, are really affected by yeast, with flavors ranging from spicy to fruity to “barnyard,” depending on the microorganisms doing the fermentation work. What a wasted opportunity to use only a handful of strains when there are literally millions of untasted varieties of yeast lurking around the planet. If more brewers experimented with new yeast strains, we could soon be drinking beers that taste nothing like the beers of yesterday.

Of course, not all yeast actually turns wort into drinkable beer. Mello accepts samples from volunteers and adds each one he receives to a basic wort mixture—that is, the liquid that turns into alcohol when yeast is added. After it’s clear that fermentation is happening, Mello goes in for a taste. “People think I drink beer all day for my job, but I spend a lot of my day drinking really bad beer,” he says.

For every ten samples Mello collects, he estimates that five will contain some sort of yeast, three will make beer, and “one makes a beer you enjoy.” Some wild yeasts don’t eat maltose—a type of sugar provided by malted barley that most commercial yeasts do eat. When such wild yeasts do their fermentation thing, they leave the maltose behind, meaning the final brew is unbearably sweet. Other yeasts can leave behind a spectrum of flavors, which are the metabolic by-products of their work converting sugar to alcohol. While the flavors can be lovely (think butterscotch or banana), they can just as easily go the other way (onion or ammonia).

So, why do this work? When you talk to hop breeders, they’ll tell you that breeding the next big-hit hop can be a lucrative endeavor. But creating a big-money yeast is trickier. Because yeasts reproduce asexually and are therefore easy to breed, there’s nothing to stop another brewer from scraping a bit of your proprietary yeast from a beer bottle and using it in his or her next batch, says Friedlander. Still, his brewery also collects wild yeasts, though not yet on the scale of the Mellos’ operation. “For us, it’s not about getting yeast and selling it; it’s all about the service of making better beer,” he says. “I want to be an evangelist for DIY culture.”

Friedlander is also interested in yeast from a scientific aspect: What other kinds are out there? Collecting new strains could help preserve biodiversity, especially as some of the flowers and fruits these yeasts live on struggle to adapt to climate change. Mello has partnered with the University of Washington to sequence the genomes for many of the yeasts he’s collected. They focus on yeasts that have resulted in beer or acted unusual in any other way. “Yeast is one of the better-studied organisms in the world,” says Maitreya Dunham, an associate professor of genome sciences at the University of Washington. “But of the 6,000 or so genes, there are still 1,000 that we don’t really know what they do.” With every new yeast strain, she gets closer to figuring out the function of those remaining genes.

Dunham says that home brewers and beer enthusiasts are helping to move her research forward. “It’s neat to see how creative people get with it,” she says. Mello took sterilized collection containers with him on a recent trip to Leadville, Colorado, hoping to catch the “highest yeast strain” from the continental United States, meaning he swabbed for yeast in a high-altitude meadow. From a yeast like that, Dunham may be able to figure out how to breed hardier varieties, while one swiped from the tropics may give us clues for building a yeast that can withstand a hotter planet.

Want to collect your own wild yeast? Here’s how to do it:

  1. Start with a sterilized jar. This means washing it thoroughly with soap and hot water and, preferably, letting it sit in boiling water for ten minutes.
  2. Fill the jar with a basic wort recipe. Don’t waste your fancy-pants stuff on this brew.
  3. Place the jar outside, preferably near an herb or vegetable garden or a fruit tree—this is where the more interesting yeasts could be lurking. Try to put the brew somewhere semi-dark if you can.
  4. Wait.
  5. If your beer starts to ferment (look for carbon dioxide bubbles), you’ve got yeast!
  6. Wait a few weeks to really make sure you have good fermentation before tasting your brew. If it smells bad, chuck it and start over.
  7. For full instructions, including how to isolate your yeast strain and send it to Bootleg Biology, visit

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