MAPPING THE CONCENTRATIONS OF GASEOUS ETHANOL IN THE HEADSPACE OF CHAMPAGNE GLASSES THROUGH INFRARED LASER ABSORPTION SPECTROSCOPY

Abstract

Under standard wine tasting conditions, volatile organic compounds (VOCs) responsible for the wine’s bouquet progressively invade the glass headspace above the wine surface. Most of wines being complex water/ethanol mixtures (with typically 10-15 % ethanol by volume), gaseous ethanol is therefore undoubtedly the most abundant VOC in the glass headspace [1]. Yet, gaseous ethanol is known to have a multimodal influence on wine’s perception [2]. Of particular importance to flavor perception is the effect of ethanol on the release of aroma compounds into the headspace of the beverage [1]. Moreover, triggered by the presence of ethanol in wines, the Marangoni effect increases the exhaust of flavored molecules in the glass headspace [2]. In addition, ethanol is known to modify the orthonasal detection threshold of aromas (and especially the fruity aromas [2]), and it can also trigger the trigeminal system leading to tingling and/or warm sensation [2]. Monitoring gaseous ethanol, in space and time, in the headspace of wine glasses is therefore crucial to better understand the neuro-physicochemical mechanisms responsible for aroma release and flavour perception.

For this purpose, micro-gas chromatography was used in the past to simultaneously monitor gas-phase ethanol and CO₂ in the headspace of champagne glasses, but with a relatively poor temporal resolution leading to a one-minute data sampling interval [3], [4]. Since the last decade at GSMA (Groupe de Spectrométrie Moléculaire et Atmosphérique), tunable diode laser absorption spectroscopy has shown to be a well-adapted method to accurately monitor gas-phase CO₂ in the headspace of glasses poured with champagne [5]. The tunability of semiconductor laser with current modulation provides CO₂ monitoring with a high temporal resolution of 42 measurements per seconds. Lastly, thanks to the recent interband cascade laser (ICL) technology, the CO₂ sensor was upgraded to monitor gaseous ethanol. This new quantum laser source, combined with previous technology developed for the monitoring of gas-phase CO₂, al-lowed us to simultaneously monitor gas-phase CO₂ and ethanol under standard still wine and sparkling wine tasting conditions. The first data sets obtained in the headspace of a glass poured with a standard brut-labelled Champagne wine are presented.