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. / Master of Science in Life Sciences / Nitrogen is an essential nutrient in grape growing and winemaking. Grapevines use nitrogen as a nutrient to survive and produce grapes for making wine. In winemaking, yeast turn the sugar and nitrogen in grape juice into alcohol via fermentation, using nitrogen to grow and produce other compounds that contribute to the final flavor of the wine. Understanding how nitrogen qualities and quantities in grape juice impact final wine quality is important so vineyard managers can apply nitrogen fertilizer to meet their needs. This thesis evaluates how different nitrogen quantities and qualities in the initial juice and during white wine fermentation impact the chemical and sensory properties of a final wine product. A Chardonel vineyard is being maintained for a multi-year study where the vineyard is divided for grapes in different areas of the plot to receive one of six different nitrogen fertilizer treatments. Grapes were harvested from each treatment and pressed into juice. Each lot of juice was then split in two for fermentation by one of two yeast strains for a total of 12 wines. Wines were bottled and stored for four months until sensory evaluation. Samples of juice and wine were collected and frozen before chemical analysis for nitrogen and other standard wine industry parameters. For sensory analysis, consumers were asked to taste each wine then sort them into groups based on how similar the wines were perceived to be. Chemical differences were found between wines, but they did not translate into sensory differences. Vineyard managers and winemakers can be aware that in Virginia-grown Chardonel, with modest differences in nitrogen from the vineyard treatments, differences in juice and wine chemical parameters did not impact the final wine product.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119088 |
| Date | 23 May 2024 |
| Creators | Mershon, Megan E. |
| Contributors | Food Science and Technology, Stewart, Amanda C., Chang, Elizabeth Ann Burzynski, Lahne, Jacob |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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