Oenological prefermentation practices strongly impact yeast population dynamics and alcoholic fermentation kinetics...

Yeast species of Hanseniaspora and Candida genus are predominant during the early stages of winemaking, while species of Metschnikowia, Pichia, Zygoascus, Issatchenkia, Torulaspora and other genera are present at lower population levels. The impact of common oenological practices on yeast dynamics during the prefermentative stage and the early stage of alcoholic fermentation (AF) remains elusive. In this work, the effect of four prefermentative oenological practices (clarification degree, temperature, sulphite and starter yeast addition) on yeast dynamics was evaluated in a Chardonnay grape must. The growth curves of four genus or species, namely Saccharomyces spp., Hanseniaspora spp., Candida zemplinina and Torulaspora delbrueckii, were followed by quantitative PCR. The fermentation kinetics were also recorded, as well as the production of acetic acid. Variance analysis allowed determining the effect of each practice and their interaction factors, as well as their relative importance on yeast dynamics and fermentation kinetics. Our experimental design showed that the population dynamics of the four species were differently impacted by the oenological practices, with some species being more sensitive than others to the clarification degree (C. zemplinina), sulphite addition (Saccharomyces spp.), starter yeast inoculation (Hanseniaspora spp.) or prefermentation temperature (T. delbrueckii). Significant interaction effects between practices were revealed, highlighting the interest of experimental design allowing interaction analysis, as some factors may buffer the effect of other ones. Hanseniaspora genus showed atypical behaviour: growth dynamics showed a decrease during AF that we interpreted as early cellular lysis. In conclusion, this study provides new insights on the impact of common oenological practices on the dynamics of non-Saccharomyces yeast that will be useful for a better management of mixed fermentation between S. cerevisiae and non-Saccharomyces yeasts.