Résumé
Introduction : In Mediterranean regions, pH values are often considered too high and acidification by addition of tartaric acid is often used. A decrease in pH allows better control of wine oxidation, physico– chemical stability, microbiological development, SO2 additions (1), and affects its sensory characteristics. Correction of pH by acidification is difficult to obtain with random results up to date, principally because high levels of pH are normally related to high levels of potassium ions (K+) and not only to organic acid contents. To decrease K+ contents and consequently pH, an electromembrane process with bipolar membranes has been recently tested in wine (2). This separative technique, under the effect of a continuous current and selective membranes (cationic and bipolar), permits the extraction of K+ ions and the free acid/salified acid equilibrium is displaced towards the acid form, thus lowering pH. Sourness, astringency and bitterness are three of the main sensory attributes of red wine. Different parameters such as alcohol (3-6), sweetness, viscosity (7), tannin and proanthocyanidin composition and concentration (4,8), type and concentration of organic acids (9-11) and pH (5,6,10) have been shown to affect these sensory attributes in model solutions and wine. Sourness of wines (4,12) and acid aqueous solutions (10,13) is dependent of pH, and is also elicited by the concentration and anion species of the acid (10). Lowering the pH of wines (3,6,12) or model solutions (12) has no effect on bitterness. Adding acid has also been reported to increase the astringency of wine (5,12) and model solutions (10,12). Astringency elicited by acids is related to pH in aqueous solutions (10,13,14), and in white wine, but not in red wine (14). Wine micro-oxygenation may increase coarseness and colour intensity in a first phase, to later soften tannins (15). After a 6 month treatment of 0.75 to 3 ml/l/month micro-oxygenation, moutounet et al. (16) observed a positive action over the hard and drying expression of red wines, together with a gain of structure. The evolution of native anthocyanins and their conversion to ethyl-bridged anthocyanin–flavanol adducts following wine microoxygenation have been reported (17). Involvement of tannins in these reactions may explain in part the decrease of astringency in wines. This research was conducted primarily to investigate the effects of a pH decrease obtained by an electromembrane process on sourness, bitterness and astringency perception in red wine after a 9 months storage. This was achieved by descriptive sensory analysis where all three sensory attributes are evaluated at the same time to simulate a real wine tasting.