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66 p r a c t i c a l w i n e r y & v i n e ya r d a U G U S t 2 0 1 4 W I N E M A K I N G Glutathione (mg/L) 4.0 Clusters Free Run Press 1 Press 2 Se ling Tank Post Racking 14.3 6.1 3.4 3.2 10.2 End Fermenta on 64.9 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 Harvest 2013 Trials—Sauvignon Blanc Hand-harvested Sauvignon Blanc grapes were transported to a winery in half-ton bins that were dumped directly into a press. The glutathione concentration in juice from intact clusters (64.9 mg/L) was in the mid- range of Sauvignon Blanc grape samples observed in 2013, which ranged from 50 –75 mg/L. In the free run juice, most of the glutathione had disappeared. This is a consequence of juice oxidation, probably starting with crushed grapes at the bottom of the half-ton bins and continuing during press loading and draining. "Press 1" juice came from berries that were relatively undamaged until active pressing started. This juice had little time to become oxidized, explaining the higher glutathione level. Harder press cuts. "Press 2" in this example are generally lower in glutathione content, most likely due to release of additional caftaric acid and plant-oxidative enzymes from grape skins. There is evidence of additional oxidation and glutathione loss when the juice-settling tank was filled, but no evidence of significant oxidation from racking. By the end of fermentation there was a net gain of 7 mg/L (ppm), evidence of glutathione release by yeast. SUPPORT RESEARCH & WINE INDUSTRY NEEDS THROUGH THE A M E R I C A N V I N E YA R D F O U N D AT I O N P.O. Box 5779, Napa, CA., 94581 • T: (707) 252-6911 • Email info@avf.org. Visit our Web site at www.avf.org for information on funding and current research projects Finding Solutions Through Research Drs. Walker and Cousins continue to develop rootstocks resistant to phylloxera and nematodes while displaying tolerance to abiotic stressors like drought and salts, with new selections from the Walker program now available to growers. Dr. Qian and others are studying the impact of closures with dierent oxygen transmission rates on aroma development with a focus on volatile sulfur compounds during post bottling aging. This work should help the industry make informed closure selections. For a wealth of useful viticulture and enology research and information, visit AVF.org, iv.ucdavis.edu, enologyaccess.org, or ngwi.org. GLUTATHIONE PROTECTION OF WHITE WINE AROMAS Glutathione, a natural grape antioxidant, can protect the aroma and flavor of white and rosé wines and prevent premature aging. Increasing demand for white and rosé wines with fresh, fruity or floral charac- ters has led to significant winemaking challenges because the aroma com- pounds in lighter wines, such as Sauvi- gnon Blanc, are fragile and oxidation can quickly cause a loss of aroma and flavor. Many winemakers are under pressure to decrease the amount of SO 2 addition as an antioxidant while still maintain- ing protection from oxidation. With the reduced level of potential antioxidant tannin/phenolic molecules in white wines, this presents a challenge. Wines such as Riesling and barrel-aged Chardonnay have experienced premature or atypical aging as a result of oxidation. Eric Herve, ETS Laboratories, St. Helena, Calif. BY