Fermentation of the grape must into wine is one of the most important steps in winemaking. Selected yeast strains of Saccharomyces cerevisiae have been used for many years to ensure complete and even fermentations. The formation of volatile compounds also occurs during fermentation and will influence the sensory perception of the wine. The main objective of the research was to study the sensory and chemical composition of 1992 Oregon Riesling, Chardonnay and Pinot Noir wines fermented with different commercial S.cerevisiae strains. In the first study, Free-Choice Profiling was used to study the sensory profiles of all three varieties after 7 and 20 months of aging. This method was used in order to utilize a panel of expert winemakers for the tastings. The sensory data analyzed through Generalized Procrustes Analysis showed that some strains were similar while others were different in terms of aroma and flavor at 7 months of age. After 20 months of aging, differences and similarities were still present although the sensory profiles were different from the young wines. This last finding showed that differences are still present after a period of aging. In the second study, the chemical composition of all three varieties and the volatile composition of selected wines of Riesling and Chardonnay were studied. In both white varieties, statistical differences in titratable acidity, residual sugar, volatile acidity and malate content resulted from fermentation with different yeast strains. The volatile composition was qualitatively similar, but some quantitative differences, as relative concentration, were found. Whether or not those differences had a sensory impact was not investigated. Results of the present study showed the need for further studies in order to understand the role of yeast in flavor development. Relationships between sensory profiles and volatile composition could help winemakers to understand the influence of a selected strain on a particular variety and to select yeast strains to optimize wine quality. / Graduation date: 1995

Wines are composed of numerous compounds that are complex, making them difficult to analyze. Wine evaluation and discrimination is typically done through chemical and human sensory evaluation. Unfortunately, both of these methods are time consuming and expensive. Therefore a new rapid analysis technique for wine discrimination and analysis is desired. The electronic nose has been suggested as an alternative to current wine discrimination techniques. In this study, a quartz microbalance-based electronic nose system was utilized to analyze the overall volatile components of wine. The electronic nose was optimized for Cabernet Sauvignon and Mouvèdre wine to gain maximum sensor response from the sensors. Response surface methodology was used to determine the optimum sensor response by varying three experimental parameters: sensor temperature, sample temperature and equilibrium time. The maximum sensor response occurred at an equilibrium time of 20 min for each varietal and at a sample temperature of 55ºC and 56ºC for Cabernet Sauvignon and Mouvèdre, respectively. The optimum sensor temperature selected for this study was 40ºC for both varietals. Using the optimum sensor settings, the electronic nose was used to analyze Cabernet Sauvignon wines. Grapes were treated with ethanol spray (5%, and 10%) 13 weeks post-bloom, which has been shown to affect the overall quality of the final wine product. Wine samples were evaluated using chemical analyses, human sensory evaluation and electronic nose. Significant differences between the wines were observed based on pH, percent alcohol, and color intensity only. A consumer sensory panel consisting of 81 panelists was unable to differentiate amongst sample treatments. However, the electronic nose was able to differentiate between the control group and the treated samples 100% of the time. Canonical discriminant analysis of the data placed the 5% ethanol treatment as a sub-set of the 10% ethanol treatment. The results indicate that the electronic nose can be used as a discriminatory tool for assessing wines. / Master of Science