Towards 2D mapping of gaseous ethanol in the headspace of wine glasses by infrared laser spectrometry

Abstract

Under standard wine tasting conditions, volatile organic compounds (VOCs) responsible for the wine’s bouquet progressively invade the chemical space perceived by the consumer in the glass headspace. With usually 7-15% ethanol by volume in wines, gaseous ethanol is thus the most abundant VOC in the headspace of still wine glasses (but after gaseous CO₂ which has already been shown to be the predominant species in the glass headspace throughout the tasting of champagne and other sparkling wines [1,2]). However, gaseous ethanol plays a multimodal role in the perception of the wine bouquet via the ortho-nasal route [3]. Moreover, as a function of its abundance in the headspace of a wine glass, gaseous ethanol can induce an unpleasant tingling/burning sensation after triggering the human trigeminal system [3,4]. Monitoring gaseous ethanol in the headspace of wine glasses is therefore crucial to better understand the neuro-physicochemical mechanisms responsible for aroma release and flavor perception throughout wine tasting.

Gaseous ethanol was monitored for the first time in the headspace of champagne glasses by micro-gas chromatography (µGC), but with a very low time-resolution and at a single point in the glass headspace [5]. More recently, a sniffer-camera for visualizing ethanol vapors above a wine glass has been developed by using chemiluminescence from an enzyme-immobilized mesh [6]. These two series of works highlighted an inhomogeneous spatial distribution of ethanol in the headspace of glasses, with higher ethanol concentrations near the rim compared to the center of the wine glass, which could be attributed to the presence of wine tears along the walls of the glass. Even more recently, thanks to the recent interband cascade laser (ICL) technology, a brand-new sensor dedicated to monitoring gaseous ethanol in the headspace of wine glasses was developed and validated [7]. In the present work, this brand-new ethanol sensor was used to better apprehend how the concentration of liquid phase ethanol rules the overall evaporation of ethanol in the headspace above glasses. Real-time monitoring of gaseous ethanol was performed in the headspace of glasses dispensed with water/ethanol mixtures showing increasing concentrations of ethanol (from 0% to 100% vol.). Moreover, real-time monitoring of gaseous ethanol was also performed in the headspace of still wine and sparkling wine glasses. From the start of wine serving, and during the next minutes following, a kind of spatial- and temperature-dependent gaseous ethanol footprint was revealed in the headspace of glasses. Accordingly, the 2D mapping of gaseous ethanol was performed in the headspace of glasses, which was discussed based on the vapor-liquid equilibrium of the water/ethanol mixture combined with a diffusive 2D-model.

References

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