Physical dynamics of sludges during wine fermentation in liquid phase
Aims: The aim of this work was to study the dynamics of the sludge particles during wine fermentation in liquid phase.
Methods and results: Ninety L of Sauvignon blanc enriched with 1.8% (v/v) of sludges, inoculated with a commercial strain of S. cerevisiae, were fermented in a transparent 100 L-fermentation tank. Results showed that the physical behavior of the sludge particles is dependent on the yeast CO2 production activity. Sludge dynamics can be divided in three phases clearly linked to the yeast fermentative activity. Although a complete dispersion of the sludges occurred during the fermentation, it could be observed that either at the surface or at the bottom of the tank, the medium turbidity never ranges the initial turbidity level, due to the disruption of the medium/gross particles into fine particles during the growth phase. Fine particles rapidly re-aggregated into medium/gross particles during the stationary phase.
Conclusions: From these results, it appears that the evolution of must turbidity during fermentation is much more complex than previously expected. Sludges are only dispersed in the fermenting must during a very short phase after the initiation of cell growth.
Significance and impact of the study: This study raises the questioning of the relationship between initial must turbidity and nutrient availability in trouble musts, since sludges are completely deposited at the onset of both cell growth and fermentation. Further research works are therefore needed to study the factors which can impact sludge particle size modification and consequently sludge nutrient accessibility for yeast growth.
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