Grape solids: Lipid composition and role during alcoholic fermentation under enological conditions

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