Nicolas Delchier* and Andrew L. Waterhouse 
*University of California, Davis, CA 95616 (ndelchier@ucdavis.edu)

Color is a primary factor in red wine quality. Red wine color is due to anthocyanins extracted from grape skins during wine fermentation. Then, during aging, anthocyanins are degraded while color still remains. This phenomenon is mainly due to the reaction of anthocyanins with other molecules, leading to formation of new, more stable pigmented compounds. The aim of our study was to determine the impact of enological tannins from different plant sources on red wine color stability during storage. Pinot noir and Cabernet Sauvignon wines were produced. Ten different tannins from acacia, tara, quebracho, oak, grape, pomegranate, and tea were tested. Those differed in their chemical nature, condensed or hydrolysable. After malolactic fermentation, they were added to the wine at three different concentrations: 150, 300, or 600 mg/L). Sampling was carried out every month over six months. Color characteristics were determined by spectrophotometry. Tannin concentrations, and small and large polymeric pigment content, were determined as described (Harbertson and Adams). Finally, anthocyanins were determined by HPLC. For both wines, the primary anthocyanin was malvidin-3-O-glucoside and its content decreased over time, as did the tannin concentration. Over the same time, the color characteristic remained quite stable. The evolution of wine pigments varied depending on the nature of the added tannins. Formation of small polymeric pigment was promoted by the tannin sources in Pinot noir wines, but less so in Cabernet Sauvignon wines. For both Pinot noir and Cabernet Sauvignon, small polymeric pigment were promoted by the addition of all tannins. Our experiments suggested that enological tannins had an impact on red color stability, but the effect depends on the nature of the tannin and the wine.

Funding Support: UC Davis, Laffort