Graduate Thesis Or Dissertation

 

Development of anthocyanins and proanthocyanidins in Pinot noir grapes and their extraction into wine Public Deposited

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  • Color stability and mouth feel quality are two of the most important aspects of red wine quality. Anthocyanins and proanthocyanidins are responsible for these attributes and it has been shown that weather conditions during the growing season and grape maturity can effect these components in wine. However, investigations into proanthocyanidin development are for the most part incomplete. Although it is known that weather affects vine metabolism, it has not clearly understood how phenolics are affected by temperature and heat summation. It is generally believed that the wines made with riper grapes improve in flavor and mouth feel as a result of an "improvement" in skin tannin "ripeness". The idea of "tannin ripeness" is usually used in the wine industry to explain this phenomenon, however, no scientific explanation for this concept has been given. The objective of this project was threefold: I) Monitor phenolic development in Pinot noir grapes over three consecutive growing seasons and determine how anthocyanin and proanthocyanidin development in grapes was affected by heat summation, II) investigate the transfer of grape phenolics into wine during fermentation and maceration and III) understand how grape maturity affected wine composition with a specific focus on proanthocyanidin structure. In this study, anthocyanin and proanthocyanidin development in Vitis vinifera L. cv. Pinot noir grapes (Pommard clone) were monitored for three consecutive vintages (2001-2003). Five cluster samples (x5 replicates) were collected for analysis each week beginning approximately 4 weeks prior to veraison and continued through commercial harvest. Weather information (temperature and heat summation) showed that the growing seasons became increasingly warmer from 2001 to 2003. By harvest time, 2003 had the highest concentration of proanthocyanidins in seeds (per berry weight) in comparison with the other two vintages. Similarly, proanthocyanidins in skins had the highest concentration in 2003 (per berry weight). However, there was not difference in the concentration of flavan-3-ol monomers in seeds (per berry weight) between the three vintages. Anthocyanins were not significantly different over the three vintages. There was some relationship between the concentration of some proanthocyanidin components in grape seeds and fresh seed weight. Information of grape and wine phenolics was compared with each year's temperature. The results suggested that changes in temperature and heat summation between vintages are associated with changes in proanthocyanidin content in grapes and wine. The data indicates that it is possible to predict proanthocyanidins in wine based upon early grape analysis. However, the anthocyanin content in grapes did not correlate with either weather or the anthocyanin content in wine. The concentration of seed and skin proanthocyanidins in grapes were compared with the proportions of seed and skin proanthocyanidins found in wine. Based upon proanthocyanidin extraction from seeds and skin during winemaking, a formula to predict proanthocyanidin content in wine based upon grape analysis at harvest and veraison was developed. From this formula, Pinot noir wine contained 7.8% of the proanthocyanidins from seed and 19% of the proanthocyanidins from skin analyzed from grapes at harvest, and 3.6% of the seed proanthocyanidin and 9.7% of the skin proanthocyanidin present in grapes analyzed at veraison. Based upon the analyses of this study, coupled with several informal sensory studies conducted on wine, the results of this thesis do not support the notion that "tannin ripeness" is due to structural changes in proanthocyanidin that occur during fruit ripening. Furthermore, this thesis suggests that "tannin ripeness" is not due to differential extraction of seed and skin proanthocyanidins as a result of fruit ripening.
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