OPTIMISATION OF THE AROMATIC PROFILE OF UGNI BLANC WINE DISTILLATE THROUGH THE CONTROL OF ALCOHOLIC FERMENTATION

Abstract

The online monitoring of fermentative aromas provides a better understanding of the effect of temperature on the synthesis and the loss of these molecules. During fermentation, gas and liquid phase concentrations as well as losses and total productions of volatile compounds can be followed with an unprecedented acquisition frequency of about one measurement per hour. Access to instantaneous production rates and total production balances for the various volatile compounds makes it possible to distinguish the impact of temperature on yeast production (biological effect) from the loss of aromatic molecules due to a physical effect³. Up to now, this innovative approach has been carried out successfully on isothermal fermentations1,2. Elucidating the role of anisothermal fermentation temperature profiles is a crucial issue that may lead to a deeper understanding of the influence of temperature on yeast metabolism in relation to the synthesis of aromatic molecules. In this study, results from different temperature control strategies of fermentation with increasing and decreasing profiles are explored. These fermentations were carried out on a laboratory scale with the online monitoring tool for alcoholic fermentation leading to a powerful dataset concerning higher alcohols, acetate and ethyl esters. The anisothermal control of the fermentation temperature shows that the production of higher alcohols is slowed down with the lowering of the temperature profiles and inversely for the ascending profiles. For isoamyl acetate and ethyl hexanoate, with ascending temperature profiles, larger losses are entailed with increasing temperature during fermentation and therefore the concentration in the liquid decreases. Obviously, the phenomenon is reversed for the descending profiles which allow to combine a better production of esters with an optimized conservation in liquid phase until the end of the alcoholic fermentation while minimizing the synthesis of higher alcohols. In strong concentrations, these alcohols may represent an organoleptic defect, especially for the distillation wines in Charente⁴. After the fermentation step, the wines were microdistilled with their lees in order to reproduce the conditions of distillation in Charente. Thanks to this step, it was possible to note the aromatic richness of the lees concerning the heavy ethyl esters⁵. Moreover, the impact of the anisothermal temperature profiles quoted above is also confirmed on the aromas released from the lees by the heating process of the distillation.