APPLIED MICROBIAL AND CELL PHYSIOLOGY Reduction of volatile acidity of wines by selected yeast strains A. Vilela-Moura & D. Schuller & A. Mendes-Faia & M. Côrte-Real Received: 23 April 2008 / Revised: 25 June 2008 / Accepted: 11 July 2008 # Springer-Verlag 2008 Abstract 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 Lachan- cea 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. Keywords Volatile acidity . Deacidification . Acidic wines . Acidic grape musts . Yeast Introduction Acetic acid is the main component of volatile acidity and is critical for wine quality. Its concentration in wines is approximately 0.5 g l -1 and must remain below 1.1 g l -1 according to current legislation. This acid is mainly produced by bacterial spoilage in Botrytis-cinerea-infected grapes. The concentration of acetic acid bacteria can increase drastically on Botrytis-infected grapes (up to 10 7 cells per milliliter, whereas the concentration on healthy grapes ranges usually between 10 2 and 10 4 cells per milliliter). The ruptured grape berry skin, caused by the infection, allows bacteria to access the berry’ s interior. Usually, Gluconobacter species occur on grapes, but Acetobacter species can dominate on the surface of rotten grapes, using ethanol as preferential carbon source that is produced in small amounts by yeast (Du Toit 2002). Acetic acid can also be formed by yeasts during alcoholic fermentation. Enzymatic reactions that can lead to acetic acid formation in yeast include (1) reversible formation from acetyl coenzyme A (CoA) and acetyl adenylate through acetyl CoA synthetase, (2) cleavage of citrate by citrate lyase, (3) production from pyruvate by pyruvate dehydrogenase, (4) reversible formation from acetyl phos- phate by acetyl kinase, and (5) oxidation of acetaldehyde by aldehyde dehydrogenase (Jost and Piendl 1975). Yeast cultures exposed to oxygen, actively synthesizing fatty acids for growth, may produce acetic acid upon entry into anaerobic conditions as a mechanism for the regeneration of free CoA needed for other biosynthetic activities (Boulton et al. 1998). Acetate formation may also play a Appl Microbiol Biotechnol DOI 10.1007/s00253-008-1616-x A. Vilela-Moura : A. Mendes-Faia CGB-IBB, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal D. Schuller : M. Côrte-Real (*) Centro de Biologia Molecular e Ambiental, Universidade do Minho, 4710-057 Braga, Portugal e-mail: mcortereal@bio.uminho.pt