Natural melanoidin in alcohol distillery effluent and synthetic melanoidin, which was prepared from glucose and glycine, showed similar elemental (CHON) compositions, spectroscopic properties and electrophoretic mobilities at various pH values. Optimal flocculation induced by FeCl3, AlCl3 or polyferric hydroxysulfate was obtained at a trivalent cation concentration of 0.04 M; excess flocculant caused color intensification of distillery effluents. Based on the electrical charge properties of melanoidins, a model is proposed for their flocculation and deflocculation induced by inorganic ions.