New Parameters to Measure Ripeness

The goals of the first year of this project were to: 1) Analyze the changes in the phenolic “profile” of extracts of grapes from unripe to ripe to overripe. Focus special attention on the levels of polymeric phenolics. 2) Determine the chemical structure of the constituents that change over this time period. 3) Prepare wines from each grape sample and compare their sensory characteristics. 4) Determine if the changes observed in the grapes parallel the wine’s content. During the 1994 vintage, two Mondavi vineyards were tised to provide samples for analysis and winemaking. Grape berries were separated into skins and seeds, the two tissues were extracted, and each extract analyzed for monomcnc (and some dimeric) phenolic compounds. By spectral analysis of all peaks, more than 90%of all the components were categorized into classes of phenolics and the amounts of each class totaled. In addition, wines prepared at different stages were analyzed in a similar manner, as well as the pomace from the fermentation. The goals outlined above has essentially been completed except tor the analysis of the polymeric constituents. However, our data was not as precise as desired due to sample variability. Consequently, it is difficult to observe any trends other than the decrease in catechin levels during ripening. This change in catecliin levels does suggest that there may be a change in the polymer distribution of flavan-3-oLs. We will address this issue by analyzing wine samples with a chromatography system that separates these compounds based on their molecular weight.