Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 47-48). Also available via the Internet.

Low nitrogen Chardonnay juice from an Oregon winery was fermented with a series of nutrient supplements, including diammonium phosphate (DAP), Fermaid K, Superfood, yeast extract, yeast hulls and thiamine. These treatments were evaluated for their contribution to the yeast assimilable nitrogen content (YANC) of the juice, which consists of the ammonium ion and α-amino acid content by NOPA (nitrogen by ophthaldialdehyde). The fermentation characteristics and the nutritional and chemical status of the finished wines were compared. Diammonium phosphate added 25 mg N/L from ammonia for every pound/1000 gallons (12.5 g/hL) used. Commercial yeast nutrient preparations were found to contribute around 10 mg N/L from ammonium ion per pound/1000 gallons (12.5 g/hL). NOPA and HPLC analysis of Superfood and Fermaid K indicated that they contributed only a small amount of amino acids. NOPA analysis of PL-50 yeast extract indicated that it may have added some nitrogen from amino acids. Nitrogenous compounds were taken up within the first few days of fermentation. Ammonium ion was depleted very quickly and did not reappear later in fermentation. Alpha-amino acids reached a low within approximately ten days of fermentation, then leveled out or increased towards the end of fermentation. Treatments containing high amounts of ammonia were observed to produce the most vigorous fermentations. These treatments were found to have the highest apparent levels of amino acids at the end of fermentation. The Control treatment, which had the lowest YANC content, appeared to utilize proline during fermentation. Sensory analysis was not conducted on the finished wines due to replication differences in reduced sulfur aroma found in preliminary screening. GC-MS analysis showed that the higher nitrogen treatments had levels of reduced sulfide compounds that were above sensory threshold, whereas moderate nitrogen treatments did not. Ethyl carbamate was not found in any of the finished wines. These data suggest that moderate levels of supplementation had a positive effect on both fermentation and finished wine quality. Higher levels of nutrient addition were effective at increasing fermentation rates but negatively affected the sulfide profile of finished wines. / Graduation date: 2001

Hen egg white lysozyme is a hydrolytic enzyme effective at preventing the growth of Gram positive bacteria by degrading the bacterial cell wall to a point of cell lysis. Investigating lysozyme as a processing tool in wine to control the growth of lactic acid bacteria and malolactic fermentation has significant commercial interest. In this project, the interactions of lysozyme with wine components and wine was evaluated along with the efficacy of lysozyme in preventing malolactic fermentation (MLF) in Oregon Pinot Noir and Chardonnay. The information from this work, together with results from similar projects, will allow the development of guidelines for lysozyme use in commercial wine. Interactions of lysozyme with wine components were evaluated by measurement of enzymatic activity in the presence of wine acids, ethanol, and phenolics. Enzyme inhibition was observed, to various degrees, with all wine components. Crude grape tannin altered the availability of free enzyme by complexing to lysozyme and forming a precipitate. In a model wine system, lysozyme activity was reduced by 50% when tannin was present. Lysozyme addition to red wine resulted in a reduction in pigmented compounds and detectable sensory differences. Wine trials evaluated the efficacy of lysozyme in completely preventing malolactic fermentation (MLF) and terminating MLF midway through fermentation in Oregon Pinot Noir and Chardonnay. Vintages from 1993 and 1994 were treated without SO₂, with SO₂, with SO₂ plus a starter culture of Leuconostoc oenos. Each lot was divided into 0 ppm lysozyme (control), 250 ppm lysozyme, 500 ppm lysozyme, and 1000 ppm lysozyme. Lactic acid bacteria were enumerated monthly, for ten months. Lysozyme prevented malolactic fermentation in all wines at the treatment levels of 500 and 1000 ppm. In the 1993 Pinot Noir, 250 ppm lysozyme prevented MLF but only delayed MLF in the 1994 vintage. Lysozyme effectively terminated MLF at a concentration between 200 and 300 ppm in both Pinot Noir and Chardonnay. / Graduation date: 1996

A field study was conducted in 1991 to determine whether high rates of cap retention in 'Chardonnay' grapes contributed to increased levels of Botrytis bunch rot (<i>Botrytis cinerea</i> Pers.), and whether spreader-sticker application enhanced cap retention. At bloom, the sticker Nu-Film 17®, or water (control), was sprayed onto single clusters at diluted ( 0.63 ml/ L ) and concentrated ( 1.26 ml/L ) label rates. After fruit set, some clusters were cleaned of caps and other flower parts with pressurized air. Cap and debris retention, berry scarring, and Botrytis rot were evaluated throughout the season. The spreader-sticker application increased debris retention only slightly. Removal of caps and debris had no effect on scarring, but reduced Botrytis bunch rot. The role of flower thrips <i>Frankliniella tritici</i> (Fitch) in causing scarring and in increasing Botrytis rot in Chardonnay grapes was explored in 1992. The insecticide methomyl (Lannate®) at a labeled rate (0.9 ml per 377 ml water per vine), or water (control), was sprayed onto selected vines twice at bloom. Berry scarring and Botrytis bunch rot were evaluated at mid-season and at harvest. The insecticide treatment reduced scarring, but did not affect Botrytis rot incidence. A survey of Virginia grape growers was conducted for 1990 and 1991, to collect information on pest and disease severity and chemical and non-chemical pest control methods. In growers’ opinions, black rot, Japanese beetle, and annual grasses were the most severe disease, insect, and weed problems respectively. Pesticides most commonly used were captan, glyphosate, and carbaryl. / Master of Science

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