Grape solids: Lipid composition and role during alcoholic fermentation under enological conditions
Résumé
Grape must contains residual solid particles after clarification, the quantity of which depends on the
clarification level. In the absence of oxygen, lipids included in solid particles are essential for yeast metabolism
and viability. Thus, we investigated the effect of lipid composition of grape solids on alcoholic fermentation. Experimental
fermentations were carried out on synthetic must in 1.1 L fermenters with the addition of grape solids
from red, rosé, or white winemaking processes. β-sitosterol was the main sterol in grape must, but the overall sterol
content of solid particles varied considerably among grape origins. Must turbidity was not representative of sterol
content. Sterol content appeared to be a determinant of maximum fermentation rate and duration when lipids were
the limiting yeast nutritional factor. This effect can be explained by the fact that sterols directly favor yeast nitrogen
assimilation (and consequently, cell growth) and improve cell viability at the end of fermentation, reducing the risk
of sluggish fermentation. Thus, accounting for the sterol content of the must may allow winemakers to improve
control of fermentations in the liquid phase.