The Secret to the Bay Area’s Most Popular Tropical Beers: GMO Yeast

If you drink a lot of Bay Area craft beer, you may have recently tasted fuzzy IPAs with extremely tangy tropical flavors and aromas, unmistakably like passion fruit and guava.

But there is no real fruit in these beers. Instead, they were fermented using a genetically modified strain of yeast called Tropics, which was bioengineered by an East Bay company specifically to produce these flavors.

In the world of craft brewing, as in many other food and beverage industries, genetically modified organisms tend to spark fierce debate, and many brewers remain reluctant to use strains from the 4-year-old startup called Berkeley Yeast. But about 250 breweries across the country have used the company’s genetically modified strains, and some insiders are warning that its scientific breakthroughs will be a game-changer for the beer industry.

In the short term, the company says it can help brewers make ever-tasting beers more efficiently. In the long term, CEO Charles Denby says his yeasts could reduce the brewing industry’s reliance on agricultural products such as hops as the climate changes.

Yeast is mixed with a high sugar solution at Berkeley Yeast.

Bronte Wittpenn/The Chronicle

Hans Eisenbeis, mission and messaging director at the Non-GMO Project, sees things differently. He doubts that craft beer drinkers, “concerned with simplicity and authenticity”, will welcome “this form of artificial flavouring”.

Yet for all the controversy that usually accompanies the use of GMOs, the arrival of Berkeley’s yeast has met with relatively little skepticism in the Bay Area, where consumers tend to prioritize anything that is natural. Even Denby was surprised by the reception.

The company sells a range of yeast strains, each offering a different result. A strain gives beers with citrus and floral notes. Another removes diacetyl, a pesky flavor that plagues some hoppy beers. Another can produce sour beer in a fraction of the time it normally takes.

By far the most popular product is Tropics, whose notes of passion fruit and guava have delighted legions of brewers, including those at local favorites like Temescal Brewing, Alvarado Street Brewing and Cellarmaker Brewing. The strain is becoming the house yeast of some breweries; Beers fermented in the tropics win prizes in competitions such as the Great American Beer Festival.

The flavors produced by Tropics are “just on a whole other level,” said Alvarado Street brewing manager JC Hill. “It’s mind-boggling how these flavors could be created without fruit.”

Berkeley Yeast co-founders Rachel Li (left), Nick Harris and CEO Charles Denby started their bioengineering business after earning doctorates from UC Berkeley.

Berkeley Yeast co-founders Rachel Li (left), Nick Harris and CEO Charles Denby started their bioengineering business after earning doctorates from UC Berkeley.

Bronte Wittpenn/The Chronicle

When Denby got into bioengineering, he expected to work on renewable fuels, not beer. He and co-founder Rachel Li met when they were doctoral students at UC Berkeley in the lab headed by Jay Keasling, a leading bioengineering scientist. Keasling’s work has largely focused on biofuels and medicinal applications, including an antimalarial compound he designed.

Like many graduate students before him, Denby took up home brewing as a hobby. He was shocked to learn how many hops were needed to brew a beer, especially the ultra-hopped IPAs currently in vogue. Denby was struck not only by the cost of buying all those hops, but also that growing them seemed so resource-intensive.

In Keasling’s lab, he and Li were already working with a class of compounds called terpenes, which can be used as diesel replacements but are also responsible for hop aromas. Scientists began to wonder: Could they genetically modify yeast to produce strong-smelling terpenes in a beer while using less hops?

Their mentor doubted the commercial feasibility because many consumers remain so wary of foods labeled as GMOs. “My first thought was: the public will never accept this,” Keasling said.

But in 2015, Denby and Li went ahead, initially creating a strain called Superbloom that produces three terpenes found in Cascade hops, a popular strain used in West Coast-style IPAs. Beers fermented by Superbloom tend to smell citrusy and floral: Berkeley Yeast describes notes as orange blossom, geranium, lime zest and lemon zest. This yeast became the basis for the startup, which Denby, Li and another Berkeley doctoral student, Nick Harris, formed in 2018.

Lab technician Kayleigh Boyd pipettes the diluted yeast before counting its cells and density.

Lab technician Kayleigh Boyd pipettes the diluted yeast before counting its cells and density.

Bronte Wittpenn/The Chronicle

As they began to interact with craft brewers, the team began to realize that there was a strong demand for beers with explosive tropical flavors, especially in hazy IPAs. “We quickly shifted our research focus to produce yeast strains that created more elaborate tropical fruit characteristics,” Denby said.

To develop a new strain, they start with an existing beer yeast, usually the beer strain known as Boddington, named after the English brewery it originated from. Then they tinker. For each new strain Berkeley Yeast produces, his team has specific compounds in mind — like those floral, lemony terpenes in Superbloom — as their end goal, and they insert DNA into the yeast that codes for enzymes that can produce these compounds.

The tinkering can be considerable. While Superbloom was developed quite quickly, Tropics took a lot more trial and error. Initial versions of Tropics not only expressed the notes of passion fruit and guava, but also “smelled like poop,” said Jeremy Roop, who leads R&D and strategy, so they had to get rid of them.

The possibilities for future flavors are seemingly endless. Eventually, Berkeley Yeast envisions a range of strains that express other distinctive fruit traits, like pineapple or peach — and brewers, Roop said, will be able to mix and match to create their own unique “fruit smoothie.”

California craft brewers have met yeast with passionate enthusiasm.

“In this industry, one person uses it, and then it has this ripple effect,” said Brad Johnson, head brewer at Moonraker Brewing in Auburn, Placer County. “We started hearing that there was this new yeast company that was ahead of the game and pushing the envelope with flavor profiles.”

Berkeley Yeast co-founder Nick Harris affixes labels to containers of ready-to-ship yeast.

Berkeley Yeast co-founder Nick Harris affixes labels to containers of ready-to-ship yeast.

Bronte Wittpenn/The Chronicle

Johnson likes Tropics, which he says makes for beers that “blow up in your face (and) you can smell from across the room.” He also calls Berkeley Yeast’s diacetyl-free strains, which negate the possibility of a beer developing an off-putting buttery flavor, as “a big weight off my shoulders.” Not all beers develop diacetyl, and there are prevention methods that don’t involve these strains of yeast, but the appeal of Berkeley Yeast’s product is its effectiveness. (By the end of the year, Roop said, all Berkeley strains will be diacetyl-free in addition to imparting their particular flavor profiles.)

Certain safety issues arise around any genetically modified organism. Li said all of the compounds produced by the Berkeley Yeast strains are food-grade flavor molecules already approved by the Food and Drug Administration, even though drinkers don’t ultimately consume the yeast itself. The compound that tastes like guava in a beer fermented in the tropics, she said, is actually the same compound that gives guava the guava taste. “We know they’re safe because people have been ingesting them in guavas for a long time,” Li said.

The team also sequences the genome of each commercial strain, Denby said, to ensure there were no major genetic changes. Their yeasts are all asexual, so they cannot reproduce with other yeasts in nature, Li added.

Even though beer drinkers don’t ingest the yeast – they simply consume a product fermented with the yeast – Eisenbeis, of the Non-GMO Project, said his organization would “advocate for more regulation, labeling and testing requirements. strict”. He expects some consumer backlash, especially in the Bay Area. Currently, the Alcohol and Tobacco Tax and Trade Bureau does not require beers brewed with bioengineered yeast to be labeled as such, as long as the yeast strains are approved by the FDA.

But so far, many brewers using Berkeley yeast have been open about it, posting descriptions of the strain on their social media accounts and in beer descriptions on their website. “We’re always super transparent,” Hill of Alvarado Street said. “I wouldn’t be afraid to talk about it with anyone.” So far, he said, no customers have objected.

The yeast is mixed with a sugar-rich solution at Berkeley Yeast's manufacturing facility.

The yeast is mixed with a sugar-rich solution at Berkeley Yeast’s manufacturing facility.

Bronte Wittpenn/The Chronicle

(Berkeley yeast strains can also be used to ferment wine, but Bay Area winemakers have been obviously hesitant to get on board. Only one local winemaker, Patrick Rue of St. Helena’s Erosion Wine Co., is open using bio-engineered strains – and he also happens to be a beer brewer.)

Other brewers, meanwhile, may delay using Berkeley strains for reasons that have nothing to do with GMO ethics.

Pacifica Brewing’s head brewer, Kim Sturdavant, said he loved the beers he tasted that were fermented with tropics, but worried the passion fruit and guava flavors would become overpowering. “If everyone is making beer that smells the same, then I don’t want to use it for that reason,” he said. “I’ve had some phenomenal beers made with (Tropics) and I see the potential for innovation. But I want my beer to not taste the same as others, I want it to have its own personality.

Still, Sturdavant said he wouldn’t rule out using Berkeley’s yeast in the future. “I sit back, waiting for other people to experiment for me,” he said. “Then I will make a decision.”

Esther Mobley is the principal wine critic for the San Francisco Chronicle. E-mail: [email protected]
Twitter: @Esther_mobley

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