New Application for Nanofiltration: Reduction of Malic Acid in Grape Must

The objective of this study was to investigate the use of a new, two-stage nanofiltration technique (demalication) to decrease the concentration of malic acid in musts. Control model trials were first performed to illustrate the chemical principles of this method. The technique was then used in an enological context with several grape varieties and compared with malolactic fermentation. With an average treatment intensity of 57% (i.e., 57 L permeate per 100 L must), the malic and tartaric acid concentrations decreased by 34% and 8%, respectively, with a very low variation of pH. This technique had a good selectivity for malic acid and the selectivity remained in wines after cold stabilization and bottling. Without malolactic fermentation, it was relatively simple to determine the intensity of demalication in must because the acidity level of the treated must was similar to the acidity level of its wine. It was also possible to decrease the titratable acidity (TA) of must by 0.6 g/L for 1 g/L malic acid to achieve a deacidification comparable to malolactic fermentation. During the treatment, must pH and TA were linear functions of initial pH and initial TA, respectively, and treatment intensity. The ease of control and the selectivity for malic acid could make this technique an interesting alternative to malolactic fermentation.