Glucose, fructose and sucrose increase the solubility of protein-tannin complexes and at high concentration, glucose and sucrose interfere with bisulphite bleaching of wine pigments

► Wines with varied sugar and tannin amounts were analysed by protein precipitation and bleaching. ► Increasing sugar decreased the precipitation of tannin and protein-precipitable polymeric pigments. ► Sugar concentration effect occurred by increasing the solubility of the tannin-protein complex. ► Sugar amounts in normal wine making will have negligible effect on protein-precipitable tannins.