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

Abstract

Grape must contains residual solid particles after clarification. The quantity of residual solid particles depends on the clarification level. In absence of oxygen, lipids included in solid particles are essential for yeast metabolism and viability. Thus, we investigated the lipid composition of grape solids to gain a better understanding of their impact during 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 there was considerable variability of overall sterol content of solid particles depending on their origin. Must turbidity was not representative of sterol content. Sterol content appeared to be determinant for maximum fermentation rate and duration when lipids were the limiting yeast nutritional factor. This impact can be explained by the fact that sterol directly i) favor yeast nitrogen assimilation and consequently cell growth, ii) improve cell viability at the end of fermentation reducing risk of sluggish fermentation. Thus, taking into account the sterol content of the must should allow winemakers to improve fermentation control of fermentations in liquid phase.