Apr 4, 2019
How winegrape growers can optimize harvests

Transforming our understanding of the chemistry and innate qualities behind great wines, Washington State University’s James Harbertson, associate professor of enology, is gaining recognition by his peers for helping winegrowers better understand when to pick their grapes and why.

Along with a team of scientists from New Zealand’s University of Auckland and the University of California, Davis, Harbertson studied various maturity stages—unripe, ripe, and overripe—in Washington Merlot grapes. He found that “ethanol concentrations,” or alcohol, outweigh fruit maturity when it comes to influencing sensory properties.

This discovery is significant, particularly to Washington winegrowers as they think about the most optimal time to harvest their fruit. “When to pick the grapes is arguably the most important decision winemakers make,” Harbertson said. “Our research will help winemakers and vineyard managers understand more clearly how those decisions change the chemistry of their wine when it comes to alcohol.”

Published in the American Journal of Enology and Viticulture, the team’s conclusions are also significant as they depart from conventional thinking. Winemakers have long considered “flavor ripeness,” or grape maturity, as one of the dominant influencers on all sensory aspects of wine from flavor and aroma, to mouthfeel and color. Harbertson’s team turns that notion on its head.

“These findings indicate that winemakers and viticulturists may be able to base harvesting and processing decisions on grape sugar concentrations (potential alcohol), with flavor ripeness having a smaller influence on wine sensory properties,” the authors reported.

The implications of the study are far reaching. “The results of our experiment are applicable across a wide range of ripeness and alcohol concentrations,” Harbertson remarked.

At its 2018 meeting, the American Society for Enology and Viticulture (ASEV) honored Harbertson’s team, citing their study as “Best Paper” in the discipline of enology.

“ASEV is the only American science-based society for wine and grapes,” Harbertson said. “It is an honor to win this award, and inspiring to know that our research is relevant and important to the Society, scientists, and industry.”

For the “Best Paper” award, committee members identify the most important paper in each of the society’s two disciplines, judging for outstanding content and substantial contributions to the field.

Read the award-winning paper here.

This study was supported by the Washington wine industry. To learn more about WSU’s Viticulture and Enology Program, click here.

– Washington State University

Photo: WSU enologist Jim Harbertson takes part in a grape crush. Harbertson’s research could help growers optimize harvest.

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