Apramita Devi, Jim Harbertson, and Andrew L Waterhouse*
*University of California, Department of Viticulture and Enology, Davis, CA, 95616 (alwaterhouse@ucdavis.edu)

Tannins are known to react with a number of substances, such as anthocyanins and sulfur dioxide, based on related chemical reactivity. These reactions lead to modifications in the tannins and affect their physical and chemical properties, potentially changing their sensory qualities. Anthocyanins have been shown to alter the sensation of astringency from tannins and reactions with sulfite eliminate tannin-protein binding. The present study examines tannin modification chemistry during winemaking and aging and their identification in aged wines. We prepared one modified tannin type, sulfonated tannins, from the reaction of commercial grape tannins in the presence of SO2 at wine pH. The sulfonation reaction was studied at varied pH (2, 3, and 4) and temperature (23, 35, and 45°C). The products were identified using LC-Q-TOF MS. Epicatechin sulfonate is the major monomeric flavanol sulfonate produced, as epicatechin is the predominant extension unit in tannins. Sulfonation was favored by low pH and high temperature. Considering the wine pH and optimal storage temperature, we estimate that in red wine, ~2% of the tannin would react in a year. So, during normal aging of tannic red wine, the conversion of tannin via sulfonation may be significant and could contribute to the decline of astringency observed in aged red wines. In addition, a database of modified tannins reported in the literature was created, and aged wines were evaluated for the presence of these modified tannins using LC-Q-TOF MS.

Funding Support: Washington State Wine Commission