The Effect of DL-Malic Acid on the Metabolism of L-Malic Acid during Wine Alcoholic Fermentation

Insufficient wine acidity can affect wine quality and stability. To overcome this problem, DL-malic acid can be added to the grape juice prior to fermentation. We have investigated the effect of DL-malic acid on wine fermentations and its influence on the final concentration of L-malic acid, naturally present in grape juice. To this end yeast strains that metabolise L-malic acid in different ways were tested and compared; namely, Schizosaccharomyces pombe (efficient L-malic acid degrader), Saccharomyces cerevisiae (non-degrader), hybrid strain S. cerevisiae x S. uvarum (intermediate degrader) and Saccharomyces uvarum (promoting L-malic acid synthesis). In all cases, D-malic acid passively entered the yeast cells and did not undergo malo-alcoholic fermentation. However, its presence in the juice, as a component of the mixture of Dand Lmalic acid (DL-malic acid), reduced the amount of L-malic acid that can be degraded or synthesised by yeasts during malo-alcoholic fermentation.