Alcohol reduction in red and white wines bynanofiltration of musts before fermentation

Abstract

One of the consequences of global warming is the early ripening of grapes which promotes a sugar content increase. Fermentation of their must leads to wines with an alcoholic degree higher than desired. The scope of this study is to select a nanofiltration (NF) technique to reduce the alcohol content of wines approximately 2 degrees by controlling the sugar content of grape must before its fermentation. For this purpose the performance of single-stage and two-stage NF processes using a spiral wound membrane unit were compared for white must (Spanish Verdejo) while for red must (Spanish Garnacha) a two-stage procedure was tested. During the singlestage NF intermittent backflush due to the osmotic pressure effect was tested. Results showed that backflushing had an undesirable effect because it increased the flux decay by disturbing the cake stabilization on the membrane. The corresponding wines obtained by adequate mixing of permeated and retained or control musts showed a 1 to 2 degrees alcohol reduction. Sensory evaluation and principal component analysis (PCA) revealed that there were no significant differences between the control and the filtered wines. Among the processes studied, the best NF technique was the two-stage process without backflush.