Metabolism of Schizosaccharomyces pombe under reduced osmotic stress conditions afforded by fed-batch alcoholic fermentation of white grape must.

Strains of Schizosaccharomyces pombe are being increasingly investigated with regards to their grape winemaking potential either in combination with the typical production yeast, Saccharomyces cerevisiae, or in monoseptic fermentations. Their ethanol tolerance and ability to degrade L-malic acid is oenologically convenient but contrasts with the comparatively high acetic acid and acetaldehyde formation potential which is considered undesirable, especially in white winemaking. The purpose of this work was to investigate the performance of a selected S. pombe strain in monoseptic femerntations of white grape must. Traditional batch fermentations were compared with an innovative and automated fed-batch fermentation technique were sugar concentrations are kept low during fermentations to decrease sugar induced osmotic stress. Because of its known effect on growth and ethanol tolerance, the effect of Mg was also tested. While Mg supplementation was not shown to significantly influence residual values of sugars, ethanol, glycerol, organic acids and acetaldehyde, the application of the fed-batch technique led to a fundamental change in yeast physiology. While glycerol values were only slightly reduced, the fed-batch approach allowed obtaining wines devoid of acetic acid whose levels were considerable in wines produced by the traditional batch technique (0.6 g/L). The work demonstrates that the acetic acid metabolism of S. pombe is associated to sugar induced osmotic stress such as for S. cerevisiae, too, and may be controlled by application of suitable fermentation techniques for winemaking.