ALCOHOLIC FERMENTATION AND COLOR OF ROSÉ WINES: INVESTIGATIONS ON THE MECHANISMS RESPONSIBLE FOR SUCH DIVERSITY

Abstract

Color is one of the key elements for the marketing of rosé wines due to their packaging in transparent bottles. Their broad color range is due to the presence of pigments belonging to phenolic compounds extracted from grapes or formed during the wine-making process. However, the mechanisms responsible for such diversity are poorly understood. The few investigations performed on rosé wines showed that their phenolic composition is highly variable, close to that of red wines for the darkest rosés but very different for light ones [1]. Moreover, large variations in the extent of color loss taking place during fermentation have been reported but the mechanisms involved and causes of such variability are unknown. The hypothesis of this work was that the color and composition of light and darker rosé wines are driven by different mechanisms occurring during alcoholic fermentation, depending on the initial must composition. To test this hypothesis, three different Vitis vinifera grape varieties commonly used for the elaboration of rosé wines in French Provence area were selected for their different color potential: Grenache, Syrah, and Cinsault. The reactions and adsorption on yeast lees of phenolic compounds and their role in color and composition changes during alcoholic fermentation of rosé musts were investigated using UV-visible spectrophotometry, ultra-high performance liquid chromatography coupled to triple quadrupole mass spectrometry, and high performance size-exclusion chromatography coupled to UV-visible spectrophotometry.

Targeted mass spectrometry analysis exhibited large varietal differences in must and wine compositions, with higher proportions of hydroxycinnamic acids in Cinsault and Grenache whereas higher concentrations of anthocyanins and flavanols were found in Syrah. Syrah must color was mainly due to anthocyanins which were partly converted to derived pigments through reactions with yeast metabolites, resulting in a limited color drop during alcoholic fermentation. UV-visible spectrophotometry and size exclusion chromatography data indicated that Grenache and Cinsault musts contained oligomeric pigments derived from hydroxycinnamic acids and flavanols which were mostly lost during fermentation due to adsorption on lees. This work highlighted the impact of must composition, reflecting varietal characteristics, on changes occurring during fermentation and consequently wine color.