Graduate Thesis Or Dissertation
 

Impact of Pre-fermentation Cold Soak Conditions on Pinot Noir Wine Quality

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fn1074279

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  • Wine volatile composition is one of the most important components of wine quality, and it is greatly affected by multiple factors, including grape variety, viticultural practices, and winemaking procedures. Pre-fermentation cold soak is one of the winemaking techniques widely undertaken by winemakers to modify their red wine quality. Imposing a pre-fermentation cold soak to grape must prior to alcoholic fermentation is typically purposed for improving the color and mouthfeel of the wine and for modifying the flavor and aroma of the wine. The studies herein were conducted to evaluate how color and aroma of the Pinot noir wine were affected by different pre-fermentation cold soak conditions. In the first study, the impact of temperature and SO2 concentrations on the population of specific non-Saccharomyces yeast during cold soaking of Pinot noir grapes and subsequent impact on wine color and aroma was investigated. Pinot noir wines were produced from grapes that were cold soaked for six days at two different temperatures (6 or 10C) with the addition of 0, 50, or 100 mg/L SO2. Wine was also produced from grapes that did not undergo cold soak. Six non-Saccharomyces yeast species, commonly isolated from grapes, were added at the start of cold soak and their populations monitored. The highest non-Saccharomyces yeast population was observed in the cold soak at 10C when no SO2 addition was made, followed by that at 6C with 0 mg/L SO2 added, both with H. uvarum being the dominate species. The growth of non-Saccharomyces yeast including H. uvarum decreased as increasing concentrations of SO2 were added to the grapes prior to cold soak. Compositions of grape juice at the end of cold soak and wine at the end of alcoholic fermentation were analyzed using High Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD), Headspace-Gas Chromatography-Flame Ionization Detector (HS-GC-FID), Headspace-Solid Phase MicroExtraction-Gas Chromatography-Pulsed Flame Photometric Detector (HS-SPME-GC-PFPD), Headspace-Solid Phase Micro-Extraction-Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS) and Stir Bar Sorptive Extraction-Gas Chromatography-Mass Spectrometry (SBSE-GC-MS). At the end of cold soak there were significant differences in a number of volatile compounds. Higher concentrations of isoamyl acetate were present in cold soaks conducted at 10C compared to 6C, while higher concentrations of phenyl ethyl acetate were present in cold soaks conducted at 10C with 100 mg/L SO2. There were also significant differences in the volatile aromas of the finished wines, particularly esters. All wines made from cold soaked grapes had significantly higher color and polymeric pigment content than the no-cold soak wine. In the second study, specific interactions between non-Saccharomyces yeast species and the potential significance to the development of volatile aromas in wine was investigated. Pinot noir wines were produced from grapes that were cold soaked with Hanseniaspora uvarum inoculated at 0, 103, and 106 cfu/mL either with or without co-inoculation of Metschnikowia fructicola at 106 cfu/mL. Wine was also produced from grapes that did not undergo cold soak with no non-Saccharomyces yeast addition. Compositions of grape juice at the end of cold soak and wine at the end of alcoholic fermentation were analyzed using HPLC-DAD, HS-GC-FID, HS-SPME-GC-PFPD, HS-SPME-GC-MS and SBSE-GC-MS. M. fructicola effectively retarded the growth of H. uvarum, although this impact was less pronounced if the initial population of H. uvarum was high (106 cfu/mL). At the end of cold soak, treatments with M. fructicola contained significantly more higher alcohols and lower acetate esters. In the finished wines there were significant differences in volatile aromas between wines made from grapes that did or did not undergo a cold soak. Pinot noir wines produced without cold soak had significantly higher ethyl esters such as ethyl butanoate, ethyl 2-methylpropanaote, and ethyl octanoate. Wines made with M. fructicola also contained significantly higher concentrations of -citronellol, as compared to the no cold soak treatment.
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