Alcohol reduction in red and white wines by nanofiltration of musts before fermentation

• Single and two-stage nanofiltration processes for sugar control in grape must.
• Test of backflush due to the osmotic pressure effect in the single-stage process.
• Blending of permeate, retentate or control must allowed alcohol reduction in wines.
• No significant differences between control and filtered wines by sensory evaluation.
• The best technique was the two-stage process without backflush.

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° 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 single-stage 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 1–2° 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.