Variation in Vitis vinifera L. cv. Cabernet Sauvignon fruit tannin concentration and extractability

In order to develop an improved understanding of the extent to which tannin chemistry can vary within a single variety, samples from 38 commercially-grown blocks (three replicates) of Cabernet Sauvignon sourced from regions of California ranging from the southern San Joaquin Valley through Sonoma, were studied. Blocks represented variation in allocation grade as assessed by the cooperating winery, and climate. Tannin information was collected from exhaustive extracts of isolated skin and seed tissue as well as from a partial extraction system designed to test the role of cell physiological integrity on tannin extractability. Extracted tannins were analyzed by acid-catalyzed cleavage in the presence of excess phloroglucinol which provided information on subunit composition and average degree of polymerization. In addition, tannin extracts were analyzed by gel permeation chromatography (GPC), which provided information on tannin size distribution and concentration. Results indicated that there was no observed geographical relationship for tannin accumulation in the seed or skin tissue. Extractability of seed tannin increased from 13% of available tannin in San Joaquin Valley fruit to 38% in Napa and Sonoma fruit. The concentration of seed tannin in the partial extraction system tripled from San Joaquin Valley to Napa and Sonoma Valleys while skin tannin extraction was similar.