Membrane contactors for measuring the alcohol content of wines: A preliminary investigation

Membrane contactors were applied to determine the alcohol content of wines through the measurement of the trans-membrane flux. The set-up used consisted of a flat cell module equipped with a commercial polypropylene membrane, where one side of the membrane was in contact with the liquid stream to analyze, while the other side was under vacuum. Hydro-alcoholic solutions were prepared by mixing different percentages of ethanol into water to have final ethanol contents of 5, 10 and 20% v/v. Stripping tests were carried out on the prepared hydro-alcoholic solutions at different temperatures and a correlation line was obtained between the transmembrane flux and the ethanol content of the feed. Then, the trans-membrane fluxes of commercial white and rose wines (both at 10.5% v/v) were measured and reported on the correlation line, so that to compare the real alcohol content with the predicted one. A good fit was observed for the white wine, whilst the flux of the rose wine was outside the correlation line. After each test on wines, a cleaning step with potassium hydroxide and citric acid allowed to recover the initial water trans-membrane flux.