In the world of craft brewing, as in many other food and drink sectors, genetically modified organisms tend to engender fierce debate, and many brewers remain reluctant to use the strains from the 4-year-old startup called Berkeley Yeast. But about 250 breweries throughout the country have used the company’s genetically modified strains, and some insiders herald its scientific breakthroughs as game changers for the beer industry.

The company sells a range of yeast strains, each offering a different outcome. One strain results in beers with citrusy and floral notes. Another eliminates diacetyl, a pesky off flavor that plagues some hoppy beers. Another can produce a sour beer in a fraction of the time it normally takes.

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

The flavors produced by Tropics are “just on a whole new level,” said Alvarado Street brewing director J.C. Hill. “It’s mind-boggling how these flavors could be created with no fruit.”

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