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70 WINES&VINES June 2015 GRAPEGROWING WINE EAST Growing Wine Quality: Thiols Adoption of vineyard practices can enhance fruit aromas in certain cultivars By Russell Moss T he varietal aromas of wines made from grapes such as Sauvignon Blanc, Petit Manseng, Riesling, Semillon, Gewürztraminer and Cayuga White are all dependent, to varying degrees, upon the tropical fruit aromas that arise from volatile thiols. This class of aromatic compounds is especially important in Sauvignon Blanc wines, within which volatile thiols are found in significantly high concentrations. This article describes methods by which the vintner can manipulate thiol concentrations in the resulting wine through vineyard practices. A subsequent article will address methods within the winery that may impact thiol concentrations. Why should we care? In Virginia, Petit Manseng, Riesling and Sauvignon Blanc are the fourth, fifth and sixth most planted white vinifera grapes respectively. Using data extrapolated from the Virginia 2013 Commercial Grape Report, the white grape varieties with the highest per-acre revenue potential for a grower are Sauvignon Blanc and Petit Manseng (Virginia Wine Marketing Office, 2014). Both of these varieties produce wines with KEY POINTS Volatile thiols give Sauvignon Blanc wines their characteristic tropical fruit aromas. Certain vine- yard practices, such as moderate water stress of vines after fruit set, can increase the amount of thiol precursors in the grapes. Researchers have found that thiols increase sig- nificantly when foliar urea is applied immediately before or after véraison to increase yeast assimi- lable nitrogen in vineyards deficient in nitrogen. Leaf removal has been found to increase thiol concentrations in Sauvignon Blanc wines, and machine-harvested fruit also has higher concentrations. Leaf removal (as seen here at Glen Manor Vineyards in Front Royal, Va.) has been shown to increase thiol concentrations in Sauvignon Blanc. JEFF WHITE/GLEN MANOR VINEYARDS