Diacetyl reduction by commercial Saccharomyces cerevisiae strains during vinification

Microbially derived diacetyl accumulation during vinification imparts a buttery wine aroma, which has stylistic implications. However, at higher concentrations diacetyl induces an aromatic off-flavour. Saccharomyces cerevisiae is able to reduce diacetyl to below the sensory threshold. Therefore, characterization of the diacetyl reduction in commercial wine yeasts creates new opportunities to manage the risk of wine associated off-flavours. Diacetyl reduction by two commercial S. cerevisiae strains was characterized in Pinot blanc grape must of the vintage 2012 with different initial diacetyl concentrations (0-50 mg/L). Highest diacetyl reduction was found in the first two days after wine yeasts were inoculated. No further decrease in diacetyl content was observed after the fourth day. All assays in which diacetyl was added showed the same final diacetyl concentration of approximately 2 mg/L. However, a significantly lower amount of diacetyl was found in grape must without adding diacetyl. The present results indicate that commercial wine yeasts are able to reduce much higher amounts of diacetyl than normally expected during the vinification procedure. However, the constant final diacetyl concentration indicates that diacetyl accumulation may be the result of wine matrix binding effects, which prevent a complete reduction by active wine yeasts. Copyright (c) 2013 The Institute of Brewing & Distilling.