Evaluation of several ultra- and nanofiltration membranes for sugar control in winemaking

Several membranes are here considered and studied in order to be applied to control of the sugar content of grape musts. This should allow decreasing somewhat the alcohol degree of wines that due to a warmer weather are being made from too mature grapes sometimes. This gives wines with a too high alcohol degree. Our objective is to reverse this degree to the original one without loosing the main appreciated characteristics of these wines. A non-aggressive technology that can be used in such a procedure consists in membrane processes. Total sugar retention and specifically glucose and fructose rejection have been studied both in must and synthetic water solutions through nanofiltration and tight ultrafiltration membranes. Also the most relevant high molecular weight (HMW) compounds of must along with their low molecular weight ones (LMW) have also been analyzed. From a detailed consideration of these retentions as a function of sugars that allow to design an adequate two steps nanofiltration process.