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72 WINES&VINES June 2015 GRAPEGROWING WINE EAST EASTERN WINE LABS Serving the Analytical needs of East Coast Wineries WWW.EASTERNWINELABS.COM Ph 609-859-4302 Cell 609-668-2854 chemist@easternwinelabs.com AOAC Member EasternWineLab_Mar09.qxp 1/22/09 9:47 AM Page 1 - B E C O PA D - Y E A S T & E N Z Y M E S - C R U S H PA D E Q U I P M E N T - S T E R I L E F I LT R AT I O N - W I N E R Y H O S E - O A K A LT E R N AT I V E S reduction in phenols with a 670% increase in glutathione was ob- served with nitrogen application. Polyphenol quinones can cause the oxidation and loss of aromatic potential (Blanchard et al., 2004). Glutathione can combat oxidation and react with quinones (Ugliano et al., 2011), and therefore thiols will be less likely to oxidize in wines made from juices of a suf- ficient YAN concentration. Foliar urea applications are an effective means of increasing YAN concentrations when applied im- mediately before or after véraison. This practice can increase YAN without incurring increased vine vigor. Dufourcq et al. (2009) ob- served significant increases in berry YAN with foliar applications of urea around véraison. The mod- ulations were variable, and in some cases modulation was not demonstrated, illustrating the un- predictable variability of plant response to fertilization. However, they also found that musts with higher YAN concentrations cor- related with higher 3MH and 3MHA concentrations in the wine. Thiols increased most significantly among nitrogen treatment plots in vineyards that were historically nitrogen deficient. They also eval- uated the co-application of foliar- applied micronized sulfur and nitrogen. On average, the re- searchers found a three- to 12-fold increase in volatile thiols in wine in the treatments sprayed with nitrogen and sulfur compared to the control. Lacroux et al. (2008) found that volatile thiols in Sauvignon Blanc wine did not increase from a soil nitrogen application of 30kg nitrogen per hectare (26.6 pounds per acre) as ammonium nitrate when compared to an unfertilized control. 4MMP was increased by a foliar urea treatment (10kg ni- trogen per hectare [8.9 pounds per acre] split over two applica- tions before véraison) when com- pared to the control, but this was the only volatile thiol to signifi- cantly increase in the foliar N treatment. 3MH, 3MHA and 4MMP were all at the highest con- centrations in wines produced from an N + S treatment (10kg nitrogen per hectare of urea and 5kg of micronized sulfur per hect- are). A tasting panel found that the N + S treatment was more aromatically intense when com- pared to the foliar N alone. It should be noted that there is a possibility to enhance the sus- ceptibility of the fruit to fungal pathogens (especially Botrytis) through foliar urea applications. However, Lacroux et al. (2008) did not find an increased inci- dence of Botrytis. While winemakers can add ni- trogen to musts that are low in YAN, questions exist as to whether naturally occurring nitrogenous compounds in musts are superior to exogenously added nitrogen. Deed et al. (2011) reported that the addition of diammonium phosphate (DAP) had no impact upon volatile thiol concentrations in an actual Sauvignon Blanc wine. In contrast, another study found that the addition of DAP in a Sauvignon Blanc must can cause Providing adequate nitrogen in the soil is one way to increase thiols. JEFF WHITE/GLEN MANOR VINEYARDS