Modest Differences in Juice Yeast Assimilable Nitrogen Concentration and Composition Influence Wine Chemistry and Impart Limited Sensory Differences in Virginia-grown Chardonel

Abstract

Nitrogen is requisite for yeast growth and metabolism during wine fermentation, and contributes to wine flavor development. Understanding how yeast assimilable nitrogen (YAN) impacts wine chemistry and sensory properties helps inform nitrogen management decisions in both the vineyard and winery. This study used Virginia-grown Chardonel, obtained from a multi-year viticulture study evaluating the impact of nitrogen fertilizer on grapevines. The objective of this work is to determine if vineyard treatments resulted in sufficient juice YAN profile differences to impart chemical and/or sensory differences in resulting wines. Grapes were combined from each field replication of six vineyard nitrogen treatments and pressed to generate six juice lots. Each juice was divided in two for triplicate fermentation using one of two Saccharomyces cerevisiae x bayanus yeast strains: EC1118 or QA23 to investigate the interactive effects of YAN and yeast strain. Juice and wine samples were frozen until chemical and UPLC-PDA amino acid analysis. Fermentation replications of each wine were combined, bottled, and stored at 4ºC for four months until evaluation via sensory sorting task with untrained panelists (n=63). Juice YAN concentrations ranged from 157-201mg N/L, a small variation in terms of commercial winemaking. Chemical differences between wines produced with the same juice but different yeast strains were larger in wines that had lower juice YAN concentrations. DISTATIS analysis of sorting results showed differences but no pattern in sensory perceptions of wines based on nitrogen profile or yeast strain. This range of nitrogen profiles shows limited impact of YAN profile on final wine quality.