The measurement of tannins and polymeric pigments during grape ripening and winemaking using a combined bisulfite bleaching protein precipitation assay

On a per berry basis proanthocyanidins from skins and seeds from Vitis vinifera L., cv. Cabernet Sauvignon, and Syrah were evaluated during berry ripening. In 1998 seeds of Cabernet Sauvignon showed highest values before veraison, after which the seed tannin declined and remained relatively constant during the four weeks before harvest. In 1999, the decline in seed tannin was slower but reached the same value at harvest that the harvest samples of 1998. In 1998 and 1999 the amount of skin tannin per berry changed very little in Cabernet Sauvingnon, and in both years the amount of tannin found in skins and seeds was equal on per berry basis at harvest. Syrah exhibited a similar pattern to Cabernet Sauvignon except that there was three times as much seed tannin per berry as skin tannin.;By combining protein precipitation and bisulfite bleaching to distinguish monomeric anthocyanins from polymeric pigments, two classes of polymeric pigments were observed in grapes and wine; small polymeric pigment (SPP) that do not precipitate with protein and large polymeric pigment (LPP) that do. The pigment composition of Cabernet Sauvignon and Syrah berries were studied during ripening and contained little polymeric pigment through out ripening and at harvest.;The amount of proanthocyanidin in three experimental wines made from Pinot noir in a commercial winery declined by up to 30% between pressing and racking. The amount of LPP and SPP increased 100% and 70% respectively between pressing and racking. In two Cabernet Sauvingon wines made from the same lot of grapes sampled at bottling and 3 years prior to bottling it was found that the amount of proanthocyanidin did not change significantly while the amount of LPP and SPP increased 300% and 20% respectively.;BSA and tannin binding capacity experiments showed that the tannin binding capacity of salivary protein was shown to be 5 times greater than BSA, however when BSA and salivary protein were in excess the total amount of proanthocyanidin bound was the same. Under the assay conditions BSA is in excess suggesting the assay measures the same amount of proanthocyanidin as bound by salivary protein.