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Nov 29, 2023

Pa. winemakers uncork new possibilities with help of Penn State researchers

In her lab at Penn State, Josephine Wee, assistant professor of food science,

In her lab at Penn State, Josephine Wee, assistant professor of food science, isolates non-Saccharomyces strains from grape samples provided by the industry to study their individual capabilities, such as whether they increase aroma compounds or acidity. The photo, taken by her student, Hung Li (Henry) Wang, shows indigenous or wild yeast and molds present on wine grapes which they isolated for their non-Saccharomyces yeast study. Credit: Hung Li (Henry) Wang. All Rights Reserved.

June 7, 2023

By Alexandra McLaughlin

UNIVERSITY PARK, Pa. — Pennsylvania winemakers are uncorking new possibilities with the help of Penn State Extension and the College of Agricultural Sciences. Their expertise serves as a vital ingredient in elevating wine quality and diversity, while fueling the growth of the state's $1.4 billion wine industry.

A notable area of focus is the exploration of non-Saccharomyces yeasts, which can unlock new flavors and aromas.

"When I first learned about non-Saccharomyces yeasts, it caught my attention," said Molly Kelly, enology extension educator with nearly 20 years of experience in clinical microbiology.

She explained that wine fermentation typically relies on alcohol-tolerant Saccharomyces yeast strains. Non-Saccharomyces strains, naturally present on fruit, can lead to spoilage and produce undesirable aromas and flavors.

To address this, researchers have identified non-Saccharomyces strains that can withstand specific conditions, such as low levels of sulfur dioxide or higher alcohol content. By inoculating these strains first, followed by the Saccharomyces yeast, winemakers can achieve distinctive aromas and flavors while ensuring successful fermentation.

Some non-Saccharomyces yeast strains may lead to a more fruit-forward character in some red wine varieties, Kelly noted. For white wines such as sauvignon blanc, these strains can contribute to increased aromatic compounds, creating a tropical flavor profile.

Winemakers can use certain non-Saccharomyces strains for biocontrol purposes to prevent spoilage, while other strains have the capacity to convert sugar into acid. Non-Saccharomyces yeast also can impact the texture of wine by producing extra polysaccharides that create a richer mouthfeel, said researchers.

While a few Pennsylvania winemakers have used non-Saccharomyces wine yeast for years, others were not familiar with them.

"Initially, winemakers were hesitant to use non-Saccharomyces yeasts in the fermentation process because it can be risky if not done in a controlled manner," said Kelly, who supports the technical needs of the Pennsylvania wine industry and leads educational programming focused on wine quality.

Kelly and her colleagues at Penn State experimented with two species of non-Saccharomyces yeasts provided by Scott Laboratories, a prominent supplier of yeast strains for the food and beverage industry. After seeing positive results, Kelly then distributed these yeasts to winemakers around Pennsylvania, asking them to compare non-Saccharomyces wine with traditional Saccharomyces fermented wines.

At the recent Pennsylvania Grape and Wine Industry Conference, Kelly asked winemakers who used the yeast to bring their wines to a panel tasting. The tasters reported enhanced aromas and mouthfeel. Kelly noted that many winemakers since have incorporated non-Saccharomyces yeast into their winemaking process.

Some non-Saccharomyces yeast strains may contribute to increased aromatic compounds in some white wine varieties, creating a tropical flavor profile. Credit: Courtesy of the Pennsylvania Winery Association. All Rights Reserved.

While companies such as Scott Laboratories focus on refining known non-Saccharomyces strains with known fermentation capabilities, Josephine Wee, assistant professor of food science, works at the ground level, discovering new potential strains for winemakers to use. She isolates non-Saccharomyces strains from grape samples provided by the industry to study their individual capabilities, such as whether they increase aroma compounds or acidity.

"When I started at Penn State, I asked, ‘How can I best contribute to my community?’" Wee said. "I quickly found that the wine and fermented beverage industries were rapidly growing and expanding in Pennsylvania. I felt that my skills and expertise could help accelerate science-driven improvement and innovation."

Wee said her team has found Pichia yeast species and Hanseniaspora yeast species particularly fascinating. She explained that these strains have co-evolved with Saccharomyces cerevisiae on wine grapes, enabling them to work together during wine fermentation. They also can produce unique flavors.

Bob Green, executive winemaker at Presque Isle Wine Cellars in Erie County, said his experience with non-Saccharomyces yeasts suggests they have potential to enhance wineries’ product lines.

"One notable instance of a spontaneous fermentation occurred with riesling, which had an amazing array of fruit notes in the finished wine," he said. "I’ve done a couple of controlled non-Saccharomyces inoculations in the past couple of harvests with good results, both for fermentation and for biocontrol, and plan on doing more this year, including a true fermentation, if conditions seem appropriate."

Wee said non-Saccharomyces yeast may help manage wine faults and provide solutions to wine quality issues caused by such factors as increased sugar accumulation in wine grapes due to impacts of climate change. She pointed to the work of her advisee, Lisa Tin, a food-science master's degree student, who is exploring the use of non-Saccharomyces yeasts to lower ethanol levels in wine when grape sugars are high, while preserving or enhancing wine flavors.

"There is so much information coming from many research efforts in all aspects of vineyard and wine production that I find it impossible to keep up with the latest. The extension team does a remarkable job of highlighting the work that is relevant to our cool-climate conditions and technical abilities and helping us find the practical application."

Bob Green, executive winemaker at Presque Isle Wine Cellars in Erie County

Green emphasized the value of Penn State Extension in disseminating this type of research to the industry.

"There is so much information coming from many research efforts in all aspects of vineyard and wine production that I find it impossible to keep up with the latest," he said. "The extension team does a remarkable job of highlighting the work that is relevant to our cool-climate conditions and technical abilities and helping us find the practical application."

For Wee, the connection between research, extension and industry is crucial.

"The mission of Penn State Extension is to provide access to science-based education to address problems and take advantage of opportunities for improvement and innovation," she said. "In line with this, research on non-Saccharomyces yeasts can help Penn State Extension educators provide the industry and community with recommendations on how to use ‘non-Sacs,’ and what it can do for winemakers."

The Pennsylvania wine industry has grown to more than 350 wineries, with some now producing beer and distilled spirits. Kelly envisions a promising future for non-Saccharomyces yeast, not just in winemaking but also in other areas.

"The goal always is to enhance the quality of Pennsylvania wines, but I believe cideries, mead makers and those making wine from hybrid grapes could benefit as well," she said. "It's worth exploring."

Chuck Gill

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