Even the tannins obtained from the grape seeds can be useful to ameliorate the phenolic composition of wine. A cooperative research by a Portuguese and a Chinese team evaluated the effect of adding tannins from seeds to the wine. They analyzed two factors: the chromatic and the antioxidant characteristics. They tested two commercial products: GSE100 and GSE300, both highly pure. Two, finally, were the grapes considered: Castelao and Tinta Miuda.