Tcontained in the wine are the main sour substances, some of which are from grape berries, such as tartaric acid, malic acid and citric aid, transferred to the wine from grape during fermentation in an unchanged way; some of which are derived from fermentation, i.e. the by-product of alcoholic fermentation, such as succinic acid, lactic acid, acetic acid and various higher fatty acids; all these acids play an decisive role in wine flavor. 2. Astringency of dry red wine is caused by phenolic compounds in wine, such as tannin and pigments. Phenolic compounds do not only endow red dry wine natural and beautiful color but also special bitterness. All these polyphenols stem from grape raw material or from the brewing technique. Grape pips contain plentiful of tannin; oak-barrel storage enables polyphenol ingredient to be extracted into the wine. Phenolic compounds engender fuller and thicker dry red wine with special nutrition and health-care effect. Harmonious sourness and bitterness make the wine more appreciative and intriguing.