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June 2015 WINES&VINES 73 a significant decrease in volatile thiol concentrations in the result- ing wine (Subileau et al., 2008). Therefore, if the fruit is nitrogen deficient coming into the winery, the winemaker will not be able to ameliorate low aromatic potential with a DAP addition and may even decrease potential varietal aroma, thus highlighting the importance of vineyard practices that correct low YAN levels. Aromas of grapefruit and tropi- cal fruits are a defining character- istic of Sauternes, which are derived from Sauvignon Blanc. Thibon et al. (2009) found a 275- fold increase in the concentration of Cys-3MH in Sauvignon Blanc juice from botrytized fruit when compared to uninfected fruit. Sar- razin et al. (2007) found a 12- to 60-fold increase of 3MH concentra- tion in wines made from botrytized fruit. Botrytis may have not been directly responsible for the produc- tion of Cys-3MH, but it may have stimulated its formation via meta- bolic pathways in the grape. Leaf removal also has been found to increase thiol concentra- tions in the resulting Sauvignon Blanc wines. Suklje et al. (2014) found a 47% average increase in volatile thiols in wines made from fruit that had been exposed by complete defoliation on the morn- ing side of the vine up to about 1 foot above the cordon, when com- pared to a shaded control. Sensory panelists found that the wines from the leaf-removal treatments were higher in the passion fruit and grapefruit aromas associated with thiols. The shaded control possessed less tropical fruit aro- mas and was perceived as having an aroma of green pepper. This green pepper aroma was associ- ated with significantly higher con- centrations of methoxypyrazines, which are known to compete with aromas arising from thiols (van Wyngaard, 2013). Harvesting method has been found to have an influence upon the concentrations of conjugated precursors and the volatile thiols in the resulting wines, with the higher concentrations of both com- ing from machine-harvested fruit (Allen et al., 2011). The exact mechanisms behind this relation- ship are not fully understood but may be due to skin contact and higher enzymatic activity occurring when the grapes are machine har- vested. If one does not machine harvest, the vintner may be able to mimic this benefit through a short period of cold soak. No study has evaluated the effect of skin contact on volatile thiols in the wine. How- ever, it has been demonstrated that the amino conjugated thiols do significantly increase in the must of cold-soaked Sauvignon Blanc (Maggu et al., 2007; Peyrot des Gachons et al., 2002). Conclusion The old adage that "it takes good fruit to make good wine" may be cliché, but it seems to hold true. A vintner who is producing wine from grape varieties that are de- pendent upon volatile thiols may wish to maximize these aromas. To achieve this aim, the vintner must start in the vineyard. In order to increase the aromatic po- tential of a thiol driven wine in the vineyard, one may choose to: • Increase exposure of clusters at fruit set with leaf removal • Supply the vine with ade- quate (but not excessive) nitrogen • Abstain from the addition of DAP in the winery • Utilize a urea and sulfur spray regime around véraison • Experiment with moderate water stress from fruit set until véraison, which might be approached through rigor- ous vineyard site selection to reduce plant available water. Volatile thiols are also im- pacted by vinification practices and will be addressed in a future article. WE A graduate of Lincoln University in New Zealand, Russell Moss is pursu- ing a master's degree in viticulture and a master's degree in enology at V i rg i n i a P o l y t e c h n i c I n s t i t u t e a n d State University in Winchester, Va. His major advisor is Dr. Tony Wolf, professor of viticulture. Moss is cur- rently investigating how foliar nitro- gen and sulfur sprays impact volatile thiols in Sauvignon Blanc and Petit Manseng. WINE EAST GRAPEGROWING Growth D O E S N ' T H A P P E N B Y A C C I D E N T . Visit www.PlanWithWaterloo.com today to find out how we can take the guesswork out of your packaging projections and help you achieve your goals in 2015. Suppliers of Wine Bottles, Corks, Caps and Closures 888-539-3922 • www.PlanWithWaterloo.com This story will be posted with references at winesandvines.com.