Abstract Caroline MerrellJames Harbertson

Impact of Berry Maturity and Alcohol Content on Wine Phenolic Hydrophobicity and Content Over Time

Caroline Merrell* and James Harbertson 
*Washington State University, Wine Science Center, 2710 Crimson Way, Richland, WA 99354-1671 (caroline.merrell@wsu.edu)

Polymeric pigments, which are responsible for stable wine color and wine astringency modification, are formed primarily through the reaction of anthocyanins and tannins during wine aging. In this study, cultivar, fruit maturity, and ethanol were varied (to vary initial anthocyanin and tannin content, as well as the ratio of the two) to determine their impact on polymeric pigment formation. Two cultivars (Syrah and Cabernet Sauvignon) that differ in their native anthocyanin and tannin content were harvested at three maturities: 20, 24 and 28 Brix. At each harvest, juice sugar was manipulated in the winery to simulate the other maturities. Wine samples were collected after fermentation and incubated at an elevated temperature (30°C) for four mos. Wines were sampled monthly to evaluate changes in phenolic content and hydrophobicity. Phenolic hydrophobicity is a new application of existing methods to measure tannin characteristics and activity, since tannin-protein interactions rely on hydrogen bonding and hydrophobic interactions. As tannin polymers increase in size, they become more hydrophilic, more efficient at precipitating protein, and are therefore more astringent. The range of initial wine A:T varied by cultivar and maturity (Cabernet Sauvignon: 0.36 to 0.93; Syrah: 1.3 to 2.1). Over time in both cultivars, anthocyanin content declined exponentially, while tannin content decreased only slightly. Wine phe-nolic hydrophobicity depended only on berry maturity and was independent of alcohol concentration. In both cultivars, ripe fruit yielded wines with significantly higher phenolic hydrophobicity, while wines from unripe fruit had the lowest phenolic hydrophobicity. For each cultivar and maturity, phenolic hydrophobicity increased as wines aged. Based on comparisons of data gathered from purified phenolic standards, our initial results suggested that the remaining phenolics in aged wine tended to be smaller. Upon further investigation, we think that loss of hydrophilic anthocyanins and tannins also helps to explain the result. 

Funding Support: Wine Research Advisory Committee, Washington Wine Commission, Washington Grape and Wine Research Program, and WSU Agricultural Research Center