Crossflow Membrane Filtration of Wines: Comparison of Performance of Ultrafiltration, Microfiltration, and Intermediate Cut-Off Membranes

Abstract

Crossflow membrane filtration experiments have been performed using three membranes: (1) a cellulose-nitrate microfiltration membrane having an average pore diameter of 0.2 µm (MF 0.2); (2) a polysulfone ultrafiltration membrane having a nominal cut-off of 100 000 daltons (UF 100); and (3) a cellulose-acetate membrane having a cut-off of 20 000 daltons (UF 20). Experiments have been carried out on a white, very light wine and a red, fullbodied wine. Retention data, evaluated for all major wine components, show that differences in membrane behavior mostly concern the colloidal and phenolic fractions, with consequences on the taste and color of wines. Colloids are fully retained by the UF 20 membrane, while they fully permeate the MF 0.2 membrane; intermediate retentions (50%-60%) were observed for the UF 100 membrane. Similarly, phenolics are strongly retained by the UF 20 membrane (70%-80% retentions of all fractions, including anthocyanins), moderately retained (20%-30% retention) by the UF 100 membrane, and practically unretained by the MF 0.2 membrane. While a partial removal of tannins from the red wine was beneficial in terms of taste, as pointed out by the sensory evaluation of astringency, the removal of anthocyanins by the UF 20 membrane determined an unacceptable loss of red wine color. Concerning the turbidity reduction, it was observed that all three membranes gave acceptable results when operating on the slightly cloudy white wine, while the performance of the MF 0.2 membrane was inadequate on the highly turbid red wine. Finally, the comparison of permeability data obtained in the red wine treatment demonstrated that the MF 0.2 membrane was largely superior to the other two membranes in that it did not retain, and therefore was not plugged by, colloids. It is concluded that ultrafiltration membranes are unsuitable for wine treatment and that the optimum cut-off probably lies around 0.1 µm, which is the lower range of pore diameter of the classical microfiltration processes.