Direct method for determining seed and skin proanthocyanidin extraction into red wine.

A method was developed for determining the amount of seed and skin proanthocyanidin extraction into wines by direct measurement. This method was based upon the analysis of proanthocyanidin cleavage products after acid catalysis in the presence of excess phloroglucinol. On the basis of the analysis of proanthocyanidin extracts from grape tissues, two observations were made as follows: (i) the seed and skin proanthocyanidin extension subunit compositions were considerably different from each other, and (ii) their composition did not vary with extraction time. Thus, by comparing the proportional extension subunit composition of proanthocyanidins in wine relative to their proportional composition in corresponding grape seed and skin, it was possible to determine the contribution of each to wine. To provide additional information, the procedure was used to investigate seed and skin proanthocyanidin extraction during commercial-scale fermentations that had undergone 4 or 10 day low temperature prefermentation skin contact prior to the onset of fermentation. The results for both fermentations indicated that the proportion of skin tannin declined during fermentation and also showed that at the end of fermentation the amount and proportion of skin tannin were the same.