Bitterness and astringency of grape and wine polyphenols

Extracts containing anthocyanins (ACN), and skin tannins (SKIN) and seed ta nnins (SEED) were prepared from Vitis vinifera cv. Cabernet Franc grapes gr own in the Loire Valley, and characterised. Phenolic fractions from Caberne t Franc wines made from three Loire Valley locations were also isolated and characterised. Bitterness and astringency of ACN, SEED and SKIN as well as the wine extracts were evaluated by time intensity procedures in citric ac id solution and in a base white wine. SEED and SKIN were equally astringent when tasted at the same concentration in spite of differences in tannin co mposition. The lower molecular weight (MW) of SEED was equal in astringency to larger MW SKIN which had a lower percentage of galloylation. The SEED f raction was slightly more bitter than the SKIN fraction in the citric acid solution, although no difference could be detected between samples in base white wine. Astringency of ACN alone was much lower than either SKIN or SEE D. Addition of ACN to either tannin fraction produced very small sensory ef fects in citric acid. in wine, addition of ACN to either SEED or SKIN incre ased astringency significantly over either fraction alone, but had no effec t on bitterness. The wine fractions differed only in astringency, which was correlated with tannin units as determined by thiolysis.