Caroline Merrell and James Harbertson*
*Washington State University, 2710 Crimson Way, Richland, WA 99354 (jfharbertson@wsu.edu)

Maturity of red grape berries is an important factor in the phenolic composition of both the fruit and the corresponding wines. Fruit maturity impacts the concentrations of tannins and anthocyanins and the ratio of anthocyanins to tannins (A:T) found in the corresponding wines. In this study, Cabernet Sauvignon grapes were harvested at soluble solids concentrations of 20, 24, and 28 Brix and made into wine (200L scale) to produce wines with different A:T ratios. Wine samples were collected in triplicate at day 10 of fermentation. The phenolic fraction was then isolated and dissolved in model wine. The model wine samples were incubated at elevated temperature (30°C) for four months and sampled to evaluate changes in anthocyanins, tannins, and polymeric pigments. Initial A:T ratios were 0.43, 0.98, and 0.68 for the 20, 24, and 28 Brix treatments, respectively. Results of two-way ANOVAs indicated that winemaking treatment and time significantly affect polymeric pigment formation and anthocyanin decline, but tannins were only affected by treatment. Anthocyanins declined significantly in all treatments (~50% decline from time 0 to one month) and a time x treatment interaction was observed for small polymeric pigment (SPP) formation, indicating that treatment impacted their formation. The 20 and 24 Brix treatments had increases in SPP throughout, while in the 28 Brix treatment, SPP only increased during the first month. Time and treatment effects were seen for the large polymeric pigment formation, which increased significantly (12.6-fold in two months). Results show picking decision alters polymeric pigment formation. The 24 and 28 Brix treatments formed similar and the greatest amount of polymeric pigments, suggesting that fruit ratios of A:T closer to 1.0 favor polymeric pigment formation in Cabernet Sauvignon wines.

Funding Support: Washington Wine Grape Funds