Yeast Assimilable Nitrogen Optimization for Cool-Climate Riesling

Abstract

Adequate yeast assimilable nitrogen (YAN) concentration is necessary for successful wine fermentation; therefore, supplementing musts with nitrogen (N) is a common industry practice. In the Finger Lakes region of New York, Riesling juice (Vitis vinifera L.) often has YAN concentrations below the 140 mg/L considered a practical minimal limit. However, little research exists that has confirmed N requirements for cool-climate cultivars and conditions. To test the influence of juice N concentration on desirable sensory characteristics, a Riesling juice of 20 Brix and 130 mg/L initial YAN was supplemented with diammonium phosphate to increase YAN to 180, 250, and 300 mg/L. Each supplemented fraction and the unaltered control were inoculated with three different Saccharomyces cerevisiae yeast strains: EC1118 and W15 (Lallemand), and Côte des Blancs (Red Star). The control concentration of 130 mg N/L was enough for these three yeast strains to complete fermentation, and further supplementation improved fermentation kinetics only for EC1118. N supplementation affected the concentration of eight of the 10 select volatile compounds analyzed in at least one of the yeast strains. Of these, the concentration of most esters increased with N supplementation, with the exception of ethyl cinnamate, which decreased. Concentrations of the higher alcohols 1-hexanol and 2-phenylethanol decreased, and decanoic acid increased, with increased N. Linalool and 1,1,6-trimethyl-1,2-dihydronaphthalene, two volatiles associated with “varietal character” in Riesling, were not affected. In a preference-ranking test, sensory panelists preferred the unsupplemented control (130 mg N/L) over the supplementation treatments for wines fermented with EC1118. No difference in preference was found for the W15 and Côte des Blancs treatments.