Reduction of volatile acidity of wines by isolated and commercial yeast strains

Abstract

The main goal of this study was to isolate and characterize wine yeasts with ability to reduce volatile acidity of wines, using a refermentation process. This enological practice consists in mixing the acidic wine with freshly crushed grapes or musts in a proportion of no more than 20-30% (v/v) or, alternatively, in the incubation of the acidic wine with the residual marc from a finished wine fermentation. From a set of 135 yeast isolates, four strains revealed ability to use glucose and acetic acid simultaneously. Three of them were identified as Saccharomyces cerevisiae and one as Lachancea thermotolerans by sequencing the D1/D2 domain of the 26S ribosomal DNA large subunit. Microsatellite analysis shows, that S. cerevisiae strains 30C and 45C are genetically very similar. With the purpose to further evaluate whether the ability to degrade acetic acid in the presence of glucose was a characteristic of the isolated strains, nine commercial S. cerevisiae strains were chosen for further analysis. From this group, the strains S26, S29 and S30 display a most similar glucose and acetic acid initial simultaneous consumption pattern and therefore were assessed in simulated refermentation assays. In a medium containing an acidic wine with high glucose/low ethanol initial concentrations, under low oxygen availability, the S. cerevisiae strain S29 is the most efficient one. Comparatively, in the same medium, L. thermotolerans 44C is able to decrease significantly acetic acid similarly to the control strain Zygosaccharomyces bailii, but only under aerobic conditions. On the other hand, in a medium containing an acidic wine and low glucose/high ethanol initial concentrations, under aerobic conditions, the S. cerevisiae strain S26 is the most efficient acid degrading strain. Notably, with the same medium, but under limited-aerobic conditions, all the S. cerevisiae strains studied display acetic acid degradation efficiencies identical to Z. bailii ISA 1307. Moreover, S. cerevisiae strains S26 and S29 also reveal capacity to decrease volatile acidity of wines with an elevated content of acetic acid under limited aerobic conditions, and even without the addition of a sugar source. In summary, the S. cerevisiae strains characterized in this work appear promising for oenological applications since they are able to decrease volatile acidity of acidic wines under the low-oxygen conditions of typical refermentation processes.