Aims:  Acetaldehyde is the major carbonyl compound formed during winemaking and has implications for sensory and colour qualities of wines as well as for the use of the wine preservative SO2. The current work investigated the degradation of acetaldehyde and SO2‐bound acetaldehyde by two commercial Oenococcus oeni starters in white wine. Methods and Results:  Wines were produced by alcoholic fermentation with commercial yeast and adjusted to pH 3.3 and 3.6. While acetaldehyde was degraded rapidly and concurrently with malic acid at both pH values, SO2‐bound acetaldehyde caused sluggish bacterial growth. Strain differences were small. Conclusions:  Efficient degradation of acetaldehyde can be achieved by commercial starters of O. oeni. According to the results, the degradation of acetaldehyde could not be separated from malolactic conversion by oenococci. While this may be desirable in white winemaking, it may be necessary to delay malolactic fermentation (MLF) in order to allow for colour development in red wines. SO2‐bound acetaldehyde itself maybe responsible for the sluggish or stuck MLF, and thus bound SO2 should be considered next to free SO2 in order to evaluate malolactic fermentability. Significance and Impact of the Study:  The current study provides new results regarding the metabolism of acetaldehyde and SO2‐bound acetaldehyde during the MLF in white wine. The information is of significance to the wine industry and may contribute to reducing the concentration of wine preservative SO2.

Acetaldehyde is a volatile flavor compound present in many fermented foods and is important in the production of red and white wines. Nine strains of the genera Lactobacillus and Oenococcus were able to metabolize acetaldehyde in a resting cell system, whereas two Pediococcus strains were not. Acetic acid and ethanol were produced from its degradation. A Lactobacillus and an Oenococcus were able to degrade SO(2)-bound acetaldehyde, as well. A coincubation of resting cells of Saccharomyces bayanus Première Cuvée and Oenococcus oeni Lo111 showed that strain Lo111 metabolized acetaldehyde produced by the yeast. The ability of malolactic bacteria to degrade free and SO(2)-bound acetaldehyde has implications for sensory and color qualities and the use of SO(2) in wine.

The ability of different wine yeast (Saccharomyces cerevisiae) to inhibit malolactic bacteria (Oenococcus oeni) and the influence of nitrogen were studied using a synthetic grape juice. Malolactic fermentation was induced in fermenting synthetic grape juice or synthetic wines inoculated with different commercial strains of S. cerevisiae. O. oeni was generally inhibited in wines that contained higher concentrations of total SO2 although many yeast strains only inhibited the bacteria during fermentation under high nitrogen conditions. Yeast produced higher amounts of SO2 during fermentation under high nitrogen conditions suggesting that nitrogen affected the malolactic fermentation by influencing yeast SO2 production. However, the production of SO2 by yeast did not always account for the inhibition of O. oeni, suggesting the presence of other inhibitory mechanisms.

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