Book Description

Vineyard site influences the chemical composition of grapes and the overall characteristics of finished wine. The intricacies of how vineyard site impacts grape and wine composition and quality are of continual interest, and many studies have been performed which aim to develop better understanding of this phenomenon. This thesis explores this concept in a unique way, by examining characteristics of vineyard sites and the qualities of the resulting musts and wines from 15 vineyard sites in California and Oregon. Each of these sites is planted with Pinot noir clone 667, and 10 of 15 sites are grafted on 101-14 Mgt rootstock. All grapes were harvested and transported to the UC Davis teaching and research winery, where they were processed and fermented under controlled experimental conditions. Vineyard sites were categorized by their soil type, growing degree days, and precipitation. Growing degree days and precipitation were calculated and observed for three vintages by using nearby California Irrigation Management Information System (CIMIS) weather stations. Additionally, cluster sizes and grape berry sizes were measured and recorded to better understand site impact on cluster and grape morphology. Vineyards located in the same American Viticulture Area (AVA) sometimes share the same soil series. Grape musts were initially characterized by chemical analysis prior to fermentation, and multivariate analysis of the initial juice chemistry was performed. In 2016, regional clustering was more apparent based on initial juice chemistry than in 2017. However, in both years, general trends of similarity exist among vineyards based on their geography. Fermentations were monitored for grapes harvested from each vineyard site in 2017 and reveal different fermentation kinetics. Temperature profiles were controlled a consistent protocol by using jacketed fermentors with heating and cooling capabilities. No correlation was determined between the amount of yeast assimilable nitrogen (YAN) and the maximum rate of fermentation. Additionally, no trend was observed between fermentation behavior and AVA. Each vineyard site appeared to ferment uniquely, with the Santa Rita Hills vineyard site fermenting at the fastest rate. All vineyard sites finished fermenting to dryness. Finished wines from the 2015 vintage were observed through aging to assess how phenolic compounds change and develop in bottle. Wines were aged in screw cap enclosed bottle and analyzed at three sample points: 3 months post-fermentation, 8 months post-fermentation, and 20 months post-fermentation. Samples were analyzed by high-performance liquid chromatography (HPLC) coupled with a diode array detector (DAD). While individual vineyards displayed different initial amounts of each phenolic compound assessed, many shared similar patterns throughout aging. When all compounds at all sample points for all vineyards are assessed together, regional grouping by AVA are evident. To understand extraction of phenolic compounds into the must and fermenting grape juice, samples were taken and analyzed by UV-Vis for the 2017 vintage. Samples were taken during cold soak, fermentation, and post-press and analyzed at wavelengths of 280nm and 520nm. Measurement at 280nm gives an approximation for total phenolic compounds and measurement at 520nm give an approximation for anthocyanin content, though other materials in fermenting must and wine also absorb at 520nm. In general, absorbance values at both wavelengths continued to increase during fermentation. For some vineyard sites, a decrease in these values was observed at the end of fermentation and post-pressing, indicating a potential plateau in extraction.