A protein precipitation assay was used to separately monitor tannin concentrations in skins and seeds of three red Vitis vinifera winegrape varieties: Cabernet Sauvignon, Syrah and Pinot noir. In 1998, seeds of Cabernet Sauvignon berries showed highest values before veraison, after which the seed tannin per berry declined and remained fairly constant during the four weeks before harvest. In 1999, the decline in seed tannin was slower but reached nearly the same value by harvest as in 1998. In 1998 and 1999, the skin tannin per berry changed little in Cabernet Sauvignon, and in both years the amount of tannin in skins and in seeds was nearly equal on a per berry basis by harvest. Syrah exhibited a pattern similar to Cabernet Sauvignon except that there was nearly three times as much seed tannin per berry as skin tannin. Results with seeds of Pinot noir in 1998 were problematic because of variation observed among replicate samples. Nevertheless, as with Cabernet Sauvignon, the amounts of tannin in seeds and skins of Pinot noir were practically the same at harvest. In 1999, tannin concentrations were measured in commercial wines made from vineyards that were monitored for tannin concentrations in the fruit. There was no relationship between the total tannin per berry and the amount of tannin in the resulting wine among the three varieties studied. Seed tannin per seed varied only 40% among the three varieties, but seed tannin per berry was different by 235%. Thus, the major factor contributing to the difference in total seed tannin per berry among the three varieties was the number of seeds per berry, rather than the amount of tannin per seed.
Acknowledgments: This research was supported by grants from the American Vineyard Foundation and the Viticulture Consortium. Cooperation provided by Robert Mondavi Winery, Acacia Winery, Saintsbury, and The R. H. Phillips Vineyard is gratefully acknowledged. This research was conducted in the Department of Viticulture & Enology, University of California, Davis.
- Copyright 2002 by the American Society for Enology and Viticulture