Abstract
Color is essential for the quality of rosé wines perception and is a key element in the consumer's purchasing act, due to their packaging in transparent glass bottles. This project aims to understand the mechanisms involved in the evolution of color during the vinification of rosé wines by analyzing the impact of processes on pigments in order to better control them.The first results obtained revealed a great diversity in the color of rosé wines, which can be explained by their very different phenolic compositions. The color of light rosé wines is mainly due to pigments derived from the reactions of anthocyanins with phenolic acids and pyruvic acid, a yeast metabolite. On the contrary, the color of dark rosé wines is due, to anthocyanins and flavanols for the red component a*, in connection with extraction, and for the yellow component b*, to oxidation products resulting from the reactivity of anthocyanins and ethanal. This first approach allowed to identify the pigments involved in the color of rosé wines in order to study them during the alcoholic fermentation. This thesis focuses on a key stage of the wine-making process, the alcoholic fermentation, which is known to have a strong impact on color. Under the experimental conditions chosen, pH, temperature and sulfite concentration during alcoholic fermentation had no significant impact on the final pigment composition of wines fermented in the laboratory. However, the mechanisms involved in alcoholic fermentation were strongly impacted by the raw material (grape variety). Moreover, the selective adsorption of certain pigments on the lees accentuated this varietal effect. Indeed, a significant part of the color of the rosé wines was adsorbed on the yeast walls, highlighting the importance of this phenomenon in the vinification of rosé wines. A final non-targeted approach allowed us to validate the alcoholic fermentation protocol in the laboratory and to confirm the previous hypotheses of the predominance of the grape variety effect on the phenomena involved during fermentation. In addition, the non-targeted approach revealed a particular composition of Cinsault with the presence of large quantities of polymerized pigments.These results allowed to account for the diversity of color of rosé wines and to progress in the understanding of the mechanisms involved during alcoholic fermentation.