Non-Saccharomyces yeast for lowering wine alcohol levels: partial aeration versus standard conditions.

Non-Saccharomyces yeasts have been suggested for use in wine production for lowering alcohol content. In this study, 23 non-Saccharomyces yeasts were investigated in laboratory-scale trials using previously frozen grape must. Both aerated and standard fermentation conditions were investigated and the fermentations were co-inoculated with a commercial Saccharomyces cerevisiae reference yeast strain. Sugar consumed for percentage alcohol formed was calculated from sugar and alcohol measurements. The non-Saccharomyces yeasts showed greater variability in sugar consumption compared with the S. cerevisiae reference yeast. Two of the yeast strains (Starmerella bacillaris and Wickerhamomyces anomalus) consumed more sugar than the S. cerevisiae reference yeast under the same conditions. These two strains were subsequently used in a small-scale wine production trial following a similar aeration and standard fermentation strategy. The wine production trials using aeration compared with the standard strategy showed shorter fermentation times, increased biomass formation and more sugar utilized for alcohol produced, but reduced wine quality. The same yeasts under standard fermentation conditions also showed increased use of sugar, but neutral or positive effects on wine quality. The S. bacillaris strain showed the most potential for use in wine production for lowering alcohol content.

Characterization of novel killer toxins secreted by wine-related non-Saccharomyces yeasts and their action on Brettanomyces spp.

Wine spoilage associated with Brettanomyces bruxellensis is a major concern for winemakers. An effective and reliable method to control the proliferation of this yeast is therefore of utmost importance. To achieve this purpose, sulphur dioxide (SO2) is commonly employed but the efficiency of this chemical compound is subject to wine composition and it can elicit allergic reactions in some consumers. Biological alternatives are therefore actively sought. The current study focused on identifying and characterizing killer toxins which are antimicrobial compounds that show potential in inhibiting B. bruxellensis in wine. Two killer toxins, CpKT1 and CpKT2, from the wine isolated yeast Candida pyralidae were identified and partially characterized. The two proteins had a molecular mass above 50kDa and exhibited killer activity against several B. bruxellensis strains especially in grape juice. They were active and stable at pH3.5-4.5, and temperatures between 15 and 25°C which are compatible with winemaking conditions. Furthermore, the activity of these killer toxins was not affected by the ethanol and sugar concentrations typically found in grape juice and wine. In addition, these killer toxins inhibited neither the Saccharomyces cerevisiae nor the lactic acid bacteria strains tested. These preliminary results indicated that the application of these toxins will have no effect on the main microbial agents that drive alcoholic and malolactic fermentations and further highlight the potential of using these toxins as agents to control the development of B. bruxellensis in grape juice or wine.