Review: Characterization and Role of Grape Solids during Alcoholic Fermentation under Enological Conditions

During wine production, grape solids have a large impact on fermentation characteristics and the organoleptic qualities of the resulting wine. We review here the research carried out on grape solids. We begin by focusing on the origin, physical characteristics and composition of these solids, and the changes in these aspects occurring during fermentation. We then consider the effect of solids on fermentation, the role of sterols, the control of solids and interactions between solids and other nutrients.Solids exert their effects on alcoholic fermentation mainly by modulating lipid supply. The balance between solid content and nitrogen is a key factor in fermentation control. The study of grape solids is recent and requires further development. Knowledge of the composition of these solids, and of sterol uptake mechanisms by yeast should facilitate improvements in fermentation control