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Genetically modified yeast yields intense hop aromas in beer, Oregon State research finds:

Oregon State University brewing researchers and a team of bioengineers have shown that a genetically modified yeast strain can alter the fermentation process to create beers with significantly more pronounced hop aromas.

"These findings could be extremely useful in creating new beer flavors and increasing the number of tools brewers have at their disposal for producing beers with strong and varied tropical flavors and aromas," said Tom Shellhammer, the Nor'Wester Professor of Fermentation Science at Oregon State.

The findings also demonstrate how synthetic biology can help protect industries and consumers from the effects of climate change, said Jeremy Roop, a co-author of the paper and a bioengineer with Berkeley Yeast, a company that develops yeast strains with enhanced fermentation traits.

"As droughts and wildfires have begun to damage the harvests of hops and other beer flavoring ingredients, engineered yeast offers a means to create these flavors in a way that is not affected by unpredictable climate events," Roop said. "They also allow brewers to utilize a fuller potential of aroma from hops thereby increasing the sustainability of both the hop growing and brewing processes."

[...] Hop-forward beers are typically achieved by adding large amounts of aromatic hops, with the essential oils in hops being the main contributor to aromas in beers. Many compounds are present in the essential oils, including thiols, which provide tropical aromas to beer.

But thiol content can significantly vary among hop varieties and different harvests. Also, a significant portion of the thiols found in hops are bound to other molecules thereby making them nonaromatic precursors. These new genetically modified yeast are designed to tap into the reservoir of aroma precursors and increase the amounts of free thiols, those that provide aromas brewers are seeking, in the finished beer.

[...] To accomplish this, the team genetically modified a brewers yeast strain to express an enzyme that increases the amount of two tropical flavored thiols produced during beer fermentation. [...]

"When I was tasting these beers my eyes popped out of my head," Shellhammer said. "This really represents a quantum shift, not just an incremental shift, in terms of the expression of these strong flavors."

The beers brewed with the genetically modified stains were described as intensely tropical and fruity, and were associated with guava, passionfruit, mango and pineapple aromas. The researchers also noted that the yeast strains didn't create any off flavors or affect the fermentation process in any negative way.

[...] The new strains are not meant as replacements for hops, instead they offer brewers a new tool for producing interesting and distinctive beers while also improving the sustainability of the entire brewing supply chain, Shellhammer said.

Journal Reference:
Molitor, Richard W., Jeremy I. Roop, Charles M. Denby, et al. 2022. The Sensorial and Chemical Changes in Beer Brewed with Yeast Genetically Modified to Release Polyfunctional Thiols from Malt and Hops [open], Fermentation 8. DOI: 10.3390/fermentation8080370

Original Submission