B. Siegmund & E. Leitner (Eds): Flavour Sci., 2018, Verlag der Technischen Universität Graz DOI: 10.3217/978-3-85125-593-5-31, CC BY-NC-ND 4.0 143 On-line coffee flavour formation analysis using PTR-ToF- MS during roasting under different atmospheres Samo Smrke 1 , Anja Rahn 1 , Alexia N. Gloess 1,2 and CHAHAN YERETZIAN 1 1 Zurich University of Applied Science, Institute of Chemistry and Biological Chemistry, Wädenswil, Switzerland 2 present address: Richterswil, Switzerland Abstract The impact of the atmosphere on the flavour formation of coffee aroma during roasting was investigated by means of on-line proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). Roasting under inert atmosphere (nitrogen) was compared to roasting under oxidative conditions (air). Roasting under air has resulted in overall higher intensities of PTR-ToF-MS time-intensity profiles for seven mass peaks, which were significantly higher in intensity for ≥30 % of the roasting duration. Conversely, to the coffee roasted in air, coffee roasted under nitrogen had an unpleasant smell and lacked the distinctive coffee aroma. The results show clear differences between the flavour formation during coffee roasting in different atmospheres and provide evidence that a certain degree of oxidation during roasting is essential to formation of coffee aroma. Introduction Coffee roasting contributes most significantly to coffee aroma by transforming the green coffee beans both physically and chemically into its characteristic end-product. Thermally induced pathways, including the Maillard reaction, generate a plethora of volatile organic compounds (VOCs) that contribute to the coffee’s characteristic aroma. During coffee roasting, these reactions occur throughout the bean, resulting in a portion of the volatiles being released into the roaster exhaust while the rest remains trapped within the bean matrix. Roaster exhaust is primarily composed of water vapour, driven off the beans through air convection. This study aims to investigate the influence of oxidative flushing of the roasting chamber during roasting on the VOC composition of the roaster exhaust gas. Previous EPR studies suggest that oxygen does not contribute to radically driven pathways during roasting [1]; however, this does not exclude it from being essential in non-radical pathways. Traditionally studied using static measurement techniques, such as gas chromatography mass spectroscopy (GC/MS), coffee aroma analysis has recently adopted more dynamic approaches, for example PTR-ToF-MS. Several groups have used PTR- ToF-MS to monitor the exhaust gas of coffee roasters. Wieland and associates [2] used this highly sensitive, time resolved technique to predict the coffee roast degree based on the evolution of the exhaust gas composition. Whereas Gloess and colleagues [3] found that the exhaust gas composition was coffee origin dependent, providing evidence that different VOC pathways were occurring. The sensitivity of PTR-ToF-MS was a key feature in the present study to investigate the impact of anaerobic and oxidative conditions on the roaster exhaust gas VOC composition. Experimental Coffee roasting Arabica coffee beans from Guatemala were used for roasting experiments. The coffee was conditioned before experiments for 20 min at 105 °C and roasted in 10 g batches. A modified pilot plant type 4E Reactor vessel (Büchi, Uster, Switzerland) was