Harnessing wild yeasts to produce refined wines

By Scott Weybright, College of Agricultural, Human & Natural Resource Sciences

Xuefei-Wang-microscope-webPULLMAN, Wash. – Wine comes from grapes, but the alcohol comes from yeast. Most wine is made by fermenting grapes with specifically chosen species of yeast, leading to predictable wines for vintners.

But wild yeasts grow naturally on grapes, and researchers at Washington State University are looking to find what impact those wild yeasts have on the finished product.

“Winemaking is more sorcery than science,” said Dean Glawe, a WSU plant pathology professor. “Part of what makes particular wines special is what’s growing on the grapes.”

“We know that grapes from some vineyards make better wines,” said Glawe, who is working with plant pathology and food science colleagues on this project. “One possibility is that yeasts in those vineyards are unusual – so we want to find them.”

Wild, rich, complex

The team has found 55 species of yeast – including a new one – on grapes from around the state. That’s more than have been found anywhere in the world, though Glawe said that is possibly because his team is looking more closely than anyone else.

A few wineries around the state produce batches of wine that rely on natural fermentation from wild yeasts – they don’t add yeasts during fermentation.

“I have discovered that the wines wild yeasts create are richer and more complex,” said Flint Nelson, winemaker at Kestrel Vintners in Prosser, Wash.

“Of course there are some risks associated from wild ferments,” he added. “You don’t know what you’re getting. There is a possibility of the native yeasts developing unpleasant aromas and flavors in the wine, and there is an even greater risk of the native yeast being unable to ferment the juice to dryness.”

Kestrel has sold a special bottling of Wild Yeast Chardonnay for several years, and Nelson said customers have always responded to it positively.

Yeast genetics

The goal for the WSU research, however, is to reduce some of the risks Nelson mentioned.

WSU graduate student Xuefei Wang picks out a frozen sample to examine for different species of wild yeast. (Photos by Scott Weybright, WSU CAHNRS)

“It’s essential for the future of natural fermentation to make consistently good wines,” Glawe said. “Research can really help with this. We can show what’s happening in the vat, barrel and bottle, so winemakers can spot things going wrong before they happen.”

Pat Okubara, plant research geneticist for the U.S. Department of Agriculture and WSU adjunct professor, said the team plans to sample the frequency of each type of yeast on grapes to learn how each species ties into good or poor wine quality.

Also, “we’re looking at the genetics of specific yeasts, both on grapes and in fermentations,” said Okubara, who will take over as lead for this research when Glawe retires later this month. “Our graduate student Xuefei Wang will then look at strains that we think make good quality wines.”

Pathology and chemistry

They haven’t published any results concerning wine yet, but they have discovered a new species of yeast in Washington vineyards, and they have published some of their early survey work.

And for greater impact, the scientists are hoping to work more with the wine industry.

“The plant pathologist’s view of making wine is, we’re rotting grapes,” Glawe said. “It’s a powerful combination to work with winemakers, who are more like chemists. We’re all learning from each other to help increase wild fermentation in the state.”



Dean Glawe, WSU plant pathology, 509-335-0619, glawe@wsu.edu
Pat Okubara, WSU research geneticist, 509-335-7824, pokubara@wsu.edu
Mari Page, Kestrel Vintners wine club manager, 509-786-2675, wcmgr@kestrelwines.com