Online monitoring of coffee roasting by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS): towards a real-time process control for a consistent roast profile

Abstract

A real-time automated process control tool for coffee roasting is presented to consistently and accurately achieve a targeted roast degree. It is based on the online monitoring of volatile organic compounds (VOC) in the off-gas of a drum roaster by proton transfer reaction timeof-flight mass spectrometry at a high time (1 Hz) and mass resolution (5,500 m/Δm at full width at half-maximum) and high sensitivity (better than parts per billion by volume). Forty-two roasting experiments were performed with the drum roaster being operated either on a low, medium or high hot-air inlet temperature (= energy input) and the coffee (Arabica from Antigua, Guatemala) being roasted to low, medium or dark roast degrees. A principal component analysis (PCA) discriminated, for each one of the three hotair inlet temperatures, the roast degree with a resolution of better than ±1 Colorette. The 3D space of the three first principal components was defined based on 23 mass spectral profiles of VOCs and their roast degree at the end point of roasting. This provided a very detailed picture of the evolution of the roasting process and allowed establishment of a predictive model that projects the onlinemonitored VOC profile of the roaster off-gas in real time onto the PCA space defined by the calibration process and, ultimately, to control the coffee roasting process so as to achieve a target roast degree and a consistent roasting.

Looking into individual coffee beans during the roasting process: direct micro-probe sampling on-line photo-ionisation mass spectrometric analysis of coffee roasting gases

“…the sensory aroma analysis for a better quality control [17,18]. In the field of coffee roasting process monitoring by soft-ionisation mass spectrometric techniques, proton-transfer-reaction mass spectrometry (PTR-MS) [18][19][20][21][22][23][24] and photo-ionisation mass spectrometry (PI-MS) [25][26][27][28] have been employed. These MS approaches can detect VOC in complex matrices without interference by fragments and inorganic bulk gases such as CO 2 , CO, N 2 and H 2 O.…”

Monitoring single coffee bean roasting by direct volatile compound analysis with proton transfer reaction time‐of‐flight mass spectrometry

“…Early release of methylpyrrole was reported in the literature during roasting of 100‐g coffee beans similar to our findings at single bean level. Because the formation pathways of the volatile compounds in coffee are quite diverse and need different activation energies, the highest increase exhibited by volatile compounds may differ depending on the process conditions . This might be affected by different volatilities of pentanedione and methylpyrrole and by the compositional differences in green beans of different geographical origin .…”

Advanced Mass Spectrometry

“…PTR-TOF In vitro and in vivo flavor release in cereal bars with varying sugar composition [148] PTR-TOF Online monitoring of coffee roasting [149] PTR-TOF Monitoring the effect of high pressure and transglutaminase treatment of milk on the evolution of flavor compounds during lactic acid fermentation [54] PTR-TOF-MS Effect of the pig rearing system on the final volatile profile of Iberian dry-cured ham [55] GC × GC-TOF Sensomics analysis of key hazelnut odorants (Corylus avellana L. "Tonda Gentile") [150] GC × GC-TOF Capture and identification of the volatile components in crude and processed herbal medicines [151] GC × GC-TOF Analysis of roasted and unroasted Pistacia terebinthus volatiles [152] [38]. The TOF-MS suitability for food analysis has been widely demonstrated.…”