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20 WINES&VINES April 2015 WINE INDUSTRY NEWS S anta Rosa, Calif.—As re- searchers continue to try and determine how the red blotch virus is spreading through vineyards, they also are starting to look at how the associated dis- ease affects grape composition and wine quality. At the Sonoma County Grape Day event held Feb. 18 in Santa Rosa, Anita Oberholster from the University of California, Davis, discussed research to better un- derstand how the virus can limit grape development and what it does to wine made with grapes from virus-positive vines in proj- ects funded by the American Vine- yard Foundation. Oberholster detailed some of the analysis being done at UC Davis on grapes from red blotch- infected vines as well as anecdotal insights picked up from the field. In extreme cases of red blotch dis- ease, vines produce pink grapes that never get past 19° Brix, Ober- holster said. In other cases, vines can test positive for the virus but show no symptoms—or symptoms will appear one vintage but not the next. Oberholster said she's hoping to continue eval- uating grapes and wine from red blotch-positive vines to help growers and winemakers better understand the disease and how to mitigate s o m e o f i t s e f f e c t s through viticultural and winemaking practices. In 2014, researchers harvested Chardonnay, Merlot and Cabernet Sauvignon grapes from vines that tested positive for the virus as well as some that did not. Most of the grapes from vines with red blotch had lower Brix levels, although exact amounts ranged from 4% less to 20% less, depending on the samples. One Chardonnay sample exhibited no difference in Brix lev- els between grapes from a virus- positive vine and one without the virus. The grapes then underwent analysis with the Adams-Harbert- son tannin assay, which found little difference between virus-positive and virus-negative grapes, even in those samples that exhibited a large difference in Brix levels. Initial testing on wines made with the grapes did find some dif- ferences: One of the Cabernet wines made with virus-positive grapes actually had more polyphe- nol compounds than the wine made of grapes harvested from a virus-negative vine, but Oberhol- ster said it definitely didn't taste any better. She told the Grape Day audi- ence she's waiting until all the wines from the project can be bottled on the same date and un- dergo a month of bottle aging to conduct a thorough sensory anal- ysis, though she did have some insights from informal tastings. The wines made with grapes from red blotch-positive fruit ex- hibited suppressed fresh fruit char- acteristics while also exhibiting more "artificial fruit" flavors. She said the wines had a marked dif- ference in taste, with virus-positive wines displaying a thinner mouth- feel that was also marked by green and "grainier" tannins. —Andrew Adams Study to Assess Effect of Red Blotch on Wine Quality UNIVERSITY OF CALIFORNIA Red blotch disease in grapevines is characterized by the appearance of red veins and leaf markings.