Grape Solids: Lipid Composition and Role during Alcoholic Fermentation under Enological Conditions

Abstract

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 lipid composition of grape solids and its effect on alcoholic fermentation. Experimental fermentations were carried out on synthetic must in 1.1 L fermenters with the addition of grape solids from red, rose, 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.