MANAGING ALCOHOL IN THE VINEYARD AND THE WINERY UNDERSTANDING THE IMPACT OF ETHANOL ON WINE FLAVOR AND THE RELATIONSHIP BETWEEN AROMA COMPOSITION AND AROMA PERCEPTION IN SAUVIGNON BLANC AND CABERNET SAUVIGNON WINES

Abstract

This work consists of two manuscripts, one published, and one ready-to-submit, that embody the same experimental purpose and design with two different well-known wine grapes, Cabernet Sauvignon and Sauvignon blanc. A review of the literature is included beforehand. Ripening and alcohol were investigated for potential impacts to wine aroma and taste. Two different methods of alcohol adjustment, pre-fermentation dilution and post-fermentation membrane filtration, were implemented at three ripening targets for two vintages. Volatile composition was determined quantitatively for the wines and was correlated with significant sensory attributes. Volatile thiols in Sauvignon blanc and methoxypyrazines in Cabernet Sauvignon were quantified in addition to esters, higher alcohols, terpenes, and C13-norisoprenoids. Harvest and alcohol as treatment factors were compared as well as alcohol adjustment method and timing.Sauvignon blanc wine aroma and taste were significantly altered by changes in ethanol concentration but had fewer distinctive aromas at later harvests. Post-fermentationdealcoholization significantly reduced the concentration of volatile esters, as did pre-fermentative dilution of the must using water. Pre-fermentative dilution with sugar solution to increase alcohol concentration led to wines with higher concentrations of volatile esters, terpenes and norisoprenoids that had noticeably higher aroma intensities of tropical fruit, grapefruit, sour candy, and alcohol as well as a hotter mouthfeel and more bitter taste. Volatile thiols 3-mercaptohexanol (3-MH) and 3-merceptohexyl acetate (3-MHA) were affected by harvest timing, not alcohol, though no clear trend was observed for differences between harvests.Unlike Sauvignon blanc wines, evaluating alcohol adjustment effects showed many aroma attributes that remain discriminating for Cabernet Sauvignon wines throughout ripening. Retro-nasal aroma, taste, and mouthfeel were affected more by changes in alcohol than ortho-nasal aroma for Cabernet Sauvignon wines. Higher alcohol wines had more bruised fruit ortho-nasal aroma and more artificial fruit, pepper, and alcohol retro-nasal aroma. Both late harvest wines and high alcohol wines were high in dark fruit aroma but late harvest wines were not described distinctively by the artificial fruit descriptor, likely due to the increased concentrations of volatile esters measured in those wines. Methoxypyrazines 2-isobutyl-3-methoxypyrazine (IBMP) and 2-isopropryl-3-methoxypyrazine (IPMP) behaved incongruently. IBMP was mostly undetectable after the early harvest but was significantly higher, when quantifiable, in all low alcohol treatment wines. IPMP was significantly higher in high alcohol wines and was detected at all harvests at similar concentration ranges. Sensorially, IBMP was highly associated with both pyrazine ortho-nasal and retro-nasal aroma while IPMP associated with bruised fruit and alcohol aromas. It is recommended to harvest early and chaptalize to improve sensory qualities of these wines if more hang time presents a conflict for the vineyard or winery. Adjusting alcohol either before or after fermentation had similar effects on aroma and volatile ester reductions. However, membrane filtration offered more precision in the final outcome