Graduate Thesis Or Dissertation
 

The impact of Saccharomyces and non-Saccharomyces yeast on the aroma and flavor of Vitis vinifera L. cv. 'Pinot Noir' wine

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  • The impact of yeast on the aroma and flavor of Vitis vinifera L. cv. 'Pinot Noir' wine was investigated. Due to the presence of naturally occurring yeast and bacteria on grapes and wine equipment, and the influence these microorganisms have on wine, a means of eliminating microorganisms from grape must was explored. High Hydrostatic Pressure (HHP) processing was investigated as a means of inactivating wine microorganisms in grape must without impacting organoleptic properties. Table grape must adjusted to 23°Brix was inoculated with wine-relevant yeast and bacteria and treated for 5 and 10 minutes at 551MPa. At both 5 and 10 minutes of pressure treatment all microorganisms were reduced to below detectable numbers. Next, wine was produced from HHP treated Pinot Noir grapes and the impact of HHP on the sensory properties of the wine was investigated. Descriptive analysis of the wines using a trained panel showed minimal significant differences between wines produced from HHP treated and untreated grape must. Chemical analysis showed no significant differences in color; however, there was a 70% increase in total phenolics in the wine produced from HHP treated must. Because the sensory effects of HHP treatment on grape must appeared to be minimal, the impact of specific yeast on Pinot Noir wine was investigated. HHP treated must was fermented in sterilized red wine micro-fermentors. The yeast strains and species studied were EC1118, RC212, Assmanshausen (AMH) (Lallemand, Montréal, Canada), MERIT.ferm, and Symphony (a blend of MERIT.ferm and Kluyveromyces thermotolerans) (Chr. Hansen, Hørsholm, Denmark). All Saccharomyces yeast strains were inoculated at approximately 10⁶cfu/mL while the non-Saccharomyces yeast was inoculated at approximately 10⁵cfu/mL. Each yeast strain was inoculated in triplicate, and a total of fifteen micro-fermentors, each containing 2.75kg of HHP treated grape must, were used. Fermentation profiles were similar between yeast strains with minimal variability between replicates. However, AMH replicates finished fermentation 24 hours after other yeast strains. After fermentation, analysis showed a significant difference in color at 520nm between the AMH and EC1118 wines. There were no other significant color differences between wines. Descriptive analysis with a trained panel indicated that yeast strain had a significant effect on the sensory profile of Pinot Noir wine. Significant sensory attributes included overall fruity aroma, red fruit aroma, dark fruit aroma, and overall fruit flavor, among others. Principle Component Analysis results showed EC1118 and RC212 trending toward high overall aroma intensities and dark fruit and jammy characteristics. MERIT.ferm also produced wines with high aroma intensities; however, they trended towards red fruit and floral characteristics. The wines produced from AMH and Symphony yeasts were not distinct and resulted in low aroma and flavor intensities in several descriptor categories. The results show that HHP processing is a viable means of inactivating microorganisms from grape must without causing large alterations in the final aroma and flavor profile of wine. The data also demonstrates the feasibility of utilizing HHP processing in conjunction with autoclavable micro-fermentors to conduct experimental red wine fermentations without the influence of native yeast and bacteria. The sensory data from yeast strain trials indicate that yeast can have a significant impact on Pinot Noir wine aroma. This data could help improve control of wine aroma profiles and help improve wine quality in the Pinot Noir industry. However, more research is needed to profile a larger array of oenological yeast strains, including non-Saccharomyces species, and to examine the effects of co-inoculation.
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