James Campbell, Aude Watrelot, Thibaut Scholasch and James Kennedy*
*Constellation Brands, 12667 Road 24, Madera, CA 93637 (james.kennedy@cbrands.com)

Tannins derived from grapes are extracted during wine production operations and are responsible for red wine astringency. Tannin structure changes throughout berry development, but it is unclear to what extent the corresponding tannin activity changes. Furthermore, knowledge of the role of berry development with regard to the corresponding tannin extractability remains incomplete. The purpose of this investigation was to determine the role of berry development on tannin extractability and activity. The development of grape berries (Vitis vinifera L. cv. Cabernet Sauvignon) in ~70 commercial vineyard blocks in Napa Valley was monitored from veraison through commercial harvest. The skin and seed of sampled berries were extracted separately and exhaustively in 2:1 (v:v) acetone:water and compared to a subsample of berries that were crushed and then partially extracted in a model wine system. Extracted tannins were analyzed to determine concentration, molecular size distribution, subunit composition, and pigmented tannin, with this information being compared to corresponding tannin activity. Tannin activity declined through much of fruit ripening, although for most blocks there was a significant increase in the latest period of berry development. Based upon tannin subunit analysis, the decline in tannin activity was associated with a proportional reduction in seed tannin extraction. From principal component analysis, tannin activity was most closely associated with tannin molecular size and pigmented tannin contribution. Based upon climatological, geographical, and vineyard management information, factors related to tannin structure and activity will be discussed. Overall, the results of this study give new insight into tannin structure-activity relationships which dominate during fruit ripening.

Funding Support: American Vineyard Foundation, California State University Agricultural Research Institute