It’s 2013 and the craft beer boom is blooming across the United States. Eager young brewers are placing huge orders for new hop varieties that will soon make IPAs ubiquitous. Citra. Mosaic. Galaxy. Beer cans are churning off distribution lines, ale is flowing from taps, and money is gushing into breweries. But then some of the brewers who ignited the craze take home their cans. They find a glass in the freezer, pop the tab, pour a beautiful head of foam, take a sip—and gag.
Stomping all over those tropical fruit notes is the unwelcome taste of fake movie theater butter. “You’d take a sip and go ‘Wait a minute, that wasn’t there before,’” says J. C. Hill, the brewer and cofounder of Alvarado Street Brewery, a craft beer phenom from Monterey, California, that soared out of the 2010s boom. “I find it to make beer utterly undrinkable,” says Ryan Hammond, head brewer at Oakland’s Temescal Brewing a few hours’ drive north, which charted a similar path.
The odious culprit was a volatile compound called diacetyl, which has a distinctive buttery flavor once common on movie theater popcorn. About 10 years ago it began appearing unexpectedly in hop-heavy beers after they had been canned, turning balanced, fruity IPAs into buttery nastiness.
Brewers like Hill and Hammond can now look back on the diacetyl crisis with some nostalgia. The foul foe has been vanquished by a quieter revolution that has swept through craft beer over the past five years: genetically-modified yeast.
Alvarado and Temescal are both customers of Berkeley Yeast, a San Francisco biotech startup that has grown alongside craft breweries. It sells a “diacetyl-free” yeast with a tiny tweak to its genetic material that makes its cells produce an enzyme called ALDC. The enzyme prevents the diacetyl proliferation that brewers speculate can appear after canning when yeast hasn’t fully fermented some hop compounds. (For a GMO-free alternative, brewers can add off-the-shelf ALDC into brewing vats, but it makes the process more complicated).
Berkeley offers a wide selection of designer yeasts, with some offering process improvements like the diacetyl-killer and others adding flavor. A strain called Tropics produces an enzyme that injects guava and passionfruit overtones. It powers Temescal’s Secret Solutions Double IPA and contributes to the “tropical melange” of Bee Gee IPA from Watts Brewing Company in Bothell, Washington. Another Berkeley strain, Sunburst, adds pineapple flavors, while Galactic produces lactic acid to create sour beers without the lengthy traditional brewing process. More controversially, the company has performed experiments suggesting that engineered yeast can make it possible to brew hoppy beer without hops at all.
Although it’s not easily noticed when quaffing a brew, Berkeley’s yeast strains have brought about perhaps the biggest shift in brewing since the now iconic Citra, Mosaic, and Galaxy hops took off in the 2010s. Craft brewers across the US have switched from traditional yeasts to Berkeley strains for some, and sometimes all, their beers. Berkeley declines to share numbers, but six craft brewers told WIRED that everyone they know in the trade is either using the startup’s strains or considering it. If you’re looking to drink a Berkeley beer, most brewers credit the company’s yeast in their marketing or labeling, especially when it’s used for flavor improvements.
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“The diacetyl-free Chico yeast from Berkeley—that’s pretty much exclusively what we use in-house for our beers,” says Tim Sciascia, head brewer at Cellarmaker Brewing, a revered San Francisco brewery. “The crew at Berkeley is messing around at a level that’s just so far beyond what anyone else is doing.”
Berkeley Yeast has its critics. Some beer traditionalists and farmers have complained that the startup is taking the art out of an ancient process and threatening the future of hop farming. Before the company had a string of award-winning brewers as customers, it was just three microbiology PhDs under fire from angry hop farmers.
The startup originated—predictably—in a garage. It was the mid-2010s, and UC Berkeley postdoctoral researcher Charles Denby was using it to learn home brewing on weekends while working on biofuels in a yeast engineering lab during the week. Discovering that hops were by far the most expensive part of home brewing inspired him to think about connecting his hobby and day job.
“That was the light bulb for me,” Denby says. He began to imagine yeast strains engineered to produce the flavors hops add to beer, potentially removing the need for hops altogether. “If I can get a yeast just to make parts per billion of these flavor compounds during an otherwise normal beer fermentation process,” he recalls thinking, “we could reduce the amount of natural resources that goes into the brewing process.”
Denby started exploring that idea with labmate Rachel Li, who turned the idea of yeast that makes hop flavors into her doctoral thesis. They founded Berkeley Yeast in 2017 with fellow biologist Nick Harris.
In 2018, Denby and Li published a peer-reviewed paper on their project with several collaborators. It described experiments that created yeast strains that produced some of the flavor compounds hops usually add to beer, using the genome-editing technique Crispr and DNA sequences from mint and basil plants. Taste tests performed with California craft brewer Lagunitas showed that beer made with the engineered strains but without hops could taste similarly hoppy to conventional brews. The paper also pointed to the resource-intensive nature of hop farming, which it said consumed about 100 billion liters of irrigation water annually in the US.
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While the startup cofounders considered hoppy-tasting but hop-free beer potentially beneficial to brewers and the environment—as Denby said in a New York Times story after the paper was published—some hop farmers felt threatened. They feared engineered yeast could end a farming tradition and hollow out the soul of brewing, a dance of microorganisms, farmers, brewers, and hops stretching back to the 11th century.
Denby declines to talk on the record about the antagonism, which caught the company by surprise, but news of the provocative idea swept through the industry. “Early on, we had hop farmers calling us saying, ‘Crap, are you going to not use hops anymore?’” says Bryan Donaldson, brewing innovation manager at Lagunitas and a coauthor on the 2018 paper. (Some hop farmers are still on edge: “One guy stood up at a hop conference this year and said, ‘We don’t like these yeasts, because these yeasts can make hop flavors. This is the Beyond Meat of beer,” Jeremy Marshall, Lagunitas head brewmaster, recalls.)Berkeley Yeast quickly pivoted. Denby and his cofounders interviewed more than 100 brewers to ask what the yeast strain of their dreams would do and found there wasn’t actually much interest in eliminating hops altogether, although some brewers wanted to reduce hop usage a little for cost reasons.
The feedback led Berkeley to focus on strains that improve efficiency, such as by removing diacetyl, or enhance natural hop flavors by adding specific compounds or enzymes. One example is the enzyme carbon-sulfur-lyase, which takes flavorless molecules present in malt and hops and frees flavorful components called thiols that in beer taste like tropical fruit. Berkeley created its Tropics strain by modifying a yeast commonly used for hazy IPAs to produce the enzyme.
Since Berkeley Yeast evolved its pitch, many hop farmers have adjusted, too, realizing that new yeasts can make it easier for brewers to highlight nuanced hop flavors that could have otherwise been too difficult to isolate with a standard yeast. “I believe we could see an even bigger push toward hops that work with these new yeast strains,” says Brian Tennis, the founder of the Hop Alliance. “As hop growers, we need to make sure we are growing what the market demands.”
Although a fixture in craft brewing, to really hit the big time Berkeley Yeast will have to win over the largest multinational beer corporations such as Anheuser-Busch InBev and Heineken. Craft brewing makes up only one-quarter of the US beer market.
Major beer companies have been testing the startup’s yeasts, cofounder Denby says, although he declines to name them. Marshall, of Lagunitas—a craft beer powerhouse now owned by brewing giant Heineken—think’s it’s only a matter of time. “Somebody is going to jump in, and we are kind of standing on the precipice of that,” he says. “I don’t know who it’s going to be, but once they do I think it’s going to become commonplace.”
Lagunitas offers beers made with Berkeley strains in its taproom, including the Martial Martian Express that features “Uncanny Pineapple” flavors, but you won’t find any in grocery stores. Marshall says major beer distributors are still unsure whether consumers will be receptive to the concept of GMO yeast and would want to know whether GMO skepticism from the 1990s and early 2000s has dissipated.
Denby says he’s confident the biggest beer makers will eventually, like craft brewers, be unable to resist the creative potential and efficiency offered by engineered yeast. “It will take a longer time to scale, but the broader beer industry is going to change,” he says. Despite his original vision for the company, he’s also convinced that hops are here to stay, saying Berkeley’s goal is to complement the tradition, not threaten it.