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A Research Update from the Grapevine

September 10, 2012

Category: A Closer Look

At Fresno State’s recent “Grape Day,” leaders in wine research discussed the fruits of their labor and kept local grape growers and winemakers up to date with some practical research. The campus also showcased its fabulous viticulture educational programs, which play a major role in the economy of the Central Valley, as well as the state.

California is America’s top wine producer and the world’s fourth leading producer after France, Italy and Spain. The Wine Institute reports that the industry generates a $61.5 billion annual economic impact to California.

Since winemaking is not an easy task, enologists (those who study the science of wine and wine-making) at Fresno State and other CSUs are developing practical research and fostering innovation to ensure that California continues to make the world’s finest wines. Here are a few of the projects featured at Grape Day that have the potential to make a major impact on California’s wine industry:

Spotting Rot
Turning grapes into a fine wine is a complex scientific process. But simply put, grapes are harvested, processed, and fermented into wine, which is then aged and bottled. The magic happens during the fermentation stage—that’s when yeast helps turn grapes’ naturally occurring sugars into alcohol. Different varieties of grapes and strains of yeasts produce different types of wine.

But the process is full of nuances that can make or break a wine later on. From temperature, to fruit quality, to harvest time and procedure—every step must be executed with perfection. In an industry where efficient mechanized harvesting is now the norm, it is imperative that winemakers are meticulous about quality control.

Grape rot is one of those nuances they must track, and it is problematic. Rot is a key wine industry concern—a tiny change in grape biochemical development can be tasted later in wine.

Fresno State enology professor Roy Thornton says that grape spoilage can survive the fermentation process and end up in your glass.

“Grape rot can produce that acidic or vinegary taste sometimes experienced in wine,” said Thornton. “It’s important to gauge the amount of rot after harvesting to make sure it’s minimal. But it is a very difficult task when grapes are already loaded up in truck gondolas.”

Since the harvesting machines aren’t able to sort out bad grapes, Thornton is working on a promising new method to assess rot levels through the use of lasers. He and colleague Susan Rodriguez are utilizing the infrared spectrum to assess all of the absorbents in the juice, including the rot.

“This work is reducing the gap in our industry’s knowledge of assessing rot,” said Dr. Jim Kennedy, chair of Viticulture and Enology at Fresno State.

Cooler Weather, Quality Cabernet
Dr. Sanliang Gu, holder of Fresno State’s Ricchiuti Chair of Viticulture, discussed the practice of “Crop Forcing” vineyards.

Crop forcing addresses warm weather—a chief concern affecting the quality of wine grapes grown in regions like California’s Central Valley. High temperatures often inhibit the accumulation of organic acids, anthocyanins, tannins and phenolics—basically, all of the good stuff that makes a wine complex and rich.

Gu’s crop forcing study showed fruit ripening can be shifted to the cooler portion of the growing season in warm regions to produce better quality fruit.

Wine grapes thrive in cooler temperatures. Crop forcing delays their harvest from July/August to October/November, so they are able to mature in preferred conditions.

In order to delay harvest, Gu played a trick on his study subject: a Cabernet Sauvignon vineyard.

In June, the grape plants were hedged to remove the shoot tips. The shoot regrowth forced the early growth of buds that were supposed to come out in the next cycle. In essence, the plants were fooled into thinking it was a new year.

And the result of the crop forced harvest? A similar yield to the conventional harvest time, but a much better quality—great news for vineyards in the state’s warmer regions.

For more information about the project, check out this video about Gu’s research, which is supported by the California State University Agricultural Research Institute (ARI):

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