Compositional changes in ripening grapes: Caftaric and coutaric acids

Caftaric and coutaric acid contents (juice concentration, amounts per berry, percent of the cis forms) were investigated in samples fully protected from oxidation as ripeness increased in harvests from Grenache, French Colombard and two harvests from different vineyards of Ruby Cabernet Vitis vinifera grapes. Segregation by berry density gave sugar content (ripeness) sequences· free of other variables such as weather and provided berries of nearly identical °Brix at each ripeness level. The two Ruby Cabernet harvests, even though differing considerably in growing conditions and average °Brix level, were much closer in the details of caftaric and coutaric acid compositions to each other than to the other varieties indicating close genetic (varietal) control of these components. The proportion of coutaric to caftaric and the percentage of cis forms tend to rise toward the end of ripening. The overall ripening pattern appears to be that these components are synthesized as the berry enlarges during ripening. If the rate of synthesis is able to keep up with the berry enlargement and the content moderate (French Colombard, Ruby Cabernet), the concentration in juice stays nearly constant at a level typical for the variety. If the content is high (Grenache) and the synthesis does not keep up with berry enlargement, the concentration in juice falls as the berry content rises during ripening, but a relatively high concentration is maintained. Overripe, shriveling berries rise in concentration, but may lose caftaric acid by oxidation if tissue breakdown occurs