Grenache free-run juice was treated with pectinase to hydrolyze caftaric acid to caffeic acid and fermented as for white wine. To increase the rate, oxidation of the wine was carried out at pH 7.0 in 100% oxygen at 20°C. Samples were analyzed by reversed-phase HPLC with diode array uv-visible detection at 200 nm and peak scanning from 200 to 400 nm. Caffeic acid in the wine and in the model solutions (as controls) was oxidized, respectively, at first order rate constants 2100 and 2200 x 10-5 per hour. Similar products were observed in both systems by retention time and comparison of uv-visible spectra. Browning occurred at a faster rate in the model solution with ethanol than in the wine (3900 and 2100 x 10-5 per hour, respectively). In all instances, the brown color formed correlated well with caffeic acid consumed by oxidation (p ≤ 0.01; r 0.959; n = 5).
- Copyright 1990 by the American Society for Enology and Viticulture