Effect of refermentation conditions and micro-oxygenation on the reduction of volatile acidity by commercial S. cerevisiae strains and their impact on the aromatic profile of wines.

Herein, we evaluate the applicability of previously characterized commercial and indigenous Saccharomyces cerevisiae strains and non-S. cerevisiae species for the deacidification of white and red wines at a pilot scale. The effect of the refermentation process (mixture of acidic wine with musts from freshly crushed grapes or with residual marc) as well as micro-oxygenation (MO) on acetic acid removal efficiency and wine aromatic composition was also assessed in a red wine. The commercial strains S26 and S29 efficiently reduced both acetic acid (43 and 47%, respectively) and sugar (100%) after 264 h of refermentation of an acidic white wine that was supplemented with grape must. Similar results (60-66% of acetic acid removal) were observed for red wine deacidification using grape must, independently of MO. When residual marc was used for deacidification, strain S26 removed 40% of acetic acid, whereas strain S29 did not initiate refermentation with or without MO. Wines obtained by refermentation with the must had significantly lower acetic acid and a higher total SO(2) concentration in comparison to the wines deacidified by the grape marcs. The volatile aroma compound's composition of deacidified red wines was dependent on the refermentation process used, rather than on MO. Themarc-deacidified wine obtained by the use of strain S26 and without MO achieved the best sensory classification.When data from all analytical and sensory evaluation were combined, Principal Component Analysis (PCA) separated the wines into three distinct groups according to the strain and the refermentation process independently of MO. We successfully established an efficient and cheap enological solution for the rectification of volatile acidity of wines.

Reduction of volatile acidity of wines by selected yeast strains.

Herein, we isolate and characterize wine yeasts with the ability to reduce volatile acidity of wines using a refermentation process, which consists in mixing the acidic wine with freshly crushed grapes or musts or, alternatively, in the incubation with the residual marc. From a set of 135 yeast isolates, four strains revealed the ability to use glucose and acetic acid simultaneously. Three of them were identified as Saccharomyces cerevisiae and one as Lachancea thermotolerans. Among nine commercial S. cerevisiae strains, strains S26, S29, and S30 display similar glucose and acetic acid initial simultaneous consumption pattern and were assessed in refermentation assays. In a medium containing an acidic wine with high glucose-low ethanol concentrations, under low oxygen availability, strain S29 is the most efficient one, whereas L. thermotolerans 44C is able to decrease significantly acetic acid similar to the control strain Zygosaccharomyces bailii ISA 1307 but only under aerobic conditions. Conversely, for low glucose-high ethanol concentrations, under aerobic conditions, S26 is the most efficient acid-degrading strain, while under limited-aerobic conditions, all the S. cerevisiae strains studied display acetic acid degradation efficiencies identical to Z. bailii. Moreover, S26 strain also reveals capacity to decrease volatile acidity of wines. Together, the S. cerevisiae strains characterized herein appear promising for the oenological removal of volatile acidity of acidic wines.