Early thiamin assimilation by yeasts under enological conditions: Impact on alcoholic fermentation kinetics

The effect of early must thiamin depletion by wild yeast strains (i. e. Kloeckera and Saccharomyces species) on alcoholic fermentation kinetics was studied. Experimental conditions affecting thiamin assimilation by yeasts were first determined, using factorial designs. Then sequential and/or mixed cultures simulating wild yeast contamination, as observed during winemaking, were carried out in order to study the influence of early thiamin depletion on fermentation kinetics. The obtained results indicate that biological thiamin depletion leads to slow fermentation and may lead to sluggish or stuck fermentation. Moreover this phenomenon is amplified in media with high assimilable nitrogen contents. No release of thiamin from contaminant yeast and subsequent assimilation by fermentative yeast was observed, indicating that some enological practices (such as centrifugation of musts contaminated early) may lead to stuck fermentation.