Unveiling the power of adding sterols in wine: Optimizing alcoholic fermentation with strategic management

Excessive grape must clarification can result in sluggish alcoholic fermentation and sometimes alcoholic stuck fermentation, because of the lack of sterols for the yeasts growth. To avoid this risk, addition of sterols (ergosterol or phytosterols) can be performed, resulting in higher Saccharomyces cerevisiae viability and shorter fermentation duration. However, no dedicated study was implemented to evaluate the efficiency of different strategies of sterol management (considering sterol type, added concentration and timing of addition) during wine fermentation. So, first, to evaluate whether the response of wine yeast strains to sterol nutrition was similar according to the type and the concentration of the sterol present in the initial must, it was studied the response of a set of 10 S. cerevisiae strains in a synthetic grape must with low, medium and high concentrations of ergosterol or phytosterols. Then, the impact of the timing of sterol addition was evaluated on 2 S. cerevisiae strains with opposite behaviours. This work confirmed previous results concerning the role of ergosterol and phytosterols but also revealed new findings in this field. At first, it was confirmed that ergosterol played an important role in improving the maintenance of viable cells towards the end of fermentation, particularly in sterols-limited situations, while phytosterols demonstrated an ability to reduce acetate and glycerol production. But, in a second part, our study sheds new light on the beneficial impact of sterol addition on amino acid assimilation in yeast, leading to an increase in maximum fermentation rate, biomass production and percentage of viable cells. However, the main novelty of this research work concerns the timing of ergosterol addition. This addition at the start of fermentation in a phytosterols-free synthetic must enabled faster fermentations, as well as higher fermentative aroma synthesis, compared to addition during stationary phase Even if the impact of ergosterol additions were relatively similar for both strains tested, notable differences were found concerning amino acid assimilation and biomass production, suggesting differences in the regulation of nitrogen metabolism between both strains. These findings provide new insights into our understanding of sterol role in enological fermentation. It offers a basis for both the development of innovative strategies for sterol management and the selection of wine yeast strains under sterol starvation. •T