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 time-of-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 hot-air 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 online-monitored 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.
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Pendergrast M (2009) Coffee second only to oil? Is coffee really the second largest commodity? Tea Coffee Trade J 181:38–41
Schenker S, Perren R, Escher F, Heinemann C, Huber M, Pompizzo R (2002) Impact of roasting conditions on the formation of aroma compounds in coffee beans. J Food Sci 67(1):60–66
Baggenstoss J, Poisson L, Kaegi R, Perren R, Escher F (2008) Coffee roasting and aroma formation: application of different time–temperature conditions. J Agric Food Chem 56(14):5836–5846
Moon JK, Shibamoto T (2009) Role of roasting conditions in the profile of volatile flavor chemicals formed from coffee beans. J Agric Food Chem 57(13):5823–5831
Sivetz M, Desrosier NW (1979) Coffee bean processing. In: Coffee technology. AVI Publishing, Westport, pp 209–278
Gutierrez-Osuna R (2002) Pattern analysis for machine olfaction: a review. IEEE Sens J 2(3):189–202
Biasioli F, Yeretzian C, Dewulf J, van Langenhove H, Märk T (2011) Direct injection mass spectrometry (DIMS): adding the time dimension to (B)VOC analysis. Trac-Trends Anal Chem 30(7):1003–1017
jublot L, Linforth RST, Taylor AJ (2005) Direct atmospheric pressure chemical ionisation ion trap mass spectrometry for aroma analysis: speed, sensitivity and resolution of isobaric compounds. Int J Mass Spec 243(3):269EP–277EP
Taylor AH, Linforth RST (2003) Direct mass spectrometry of complex volatile and non-volatile flavour mixtures. Int J Mass Spec 223–224:179–191
Taylor AJ (1996) Volatile flavor release from foods during eating. CRC Crit Rev Food Sci Nutr 36(8):765–784
Linforth RST, Savary I, Pattenden B, Taylor AH (1994) Volatile compounds found in expired air during eating of fresh tomatoes and in the headspace above tomatoes. J Sci Food Agric 65:241–247
Linforth RST, Taylor A (1993) Measurement of volatile release in the mouth. Food Chem 48:115–120
Yeretzian C, Jordan A, Brevard H, Lindinger W (2000) Time-resolved headspace analysis by proton-transfer-reaction mass-spectrometry. In: Roberts DD, Taylor AJ (eds) ACS Symposium Series 763. ACS, Washington, pp 58–72
Lindinger W, Hansel A, Jordan A (1998) Proton-transfer-reaction mass spectrometry (PTR-MS): on-line monitoring of volatile organic compounds at pptv levels. Chem Soc Rev 27:347–354
Lindinger W, Hansel A, Jordan A (1998) On-line monitoring of volatile organic compounds at pptv levels by means of proton-transfer-reaction mass spectrometry (PTR-MS): medical applications, food control and environmental research. Int J Mass Spectrom Ion Process 173:191–241
Lindinger W, Hansel A (1997) Analysis of trace gases at ppb levels by proton transfer reaction mass spectrometry (PTR-MS). Plasma Sources Sci Technol 6:111–117
Hansel A, Jordan A, Holzinger R, Prazeller P, Vogel W, Lindinger W (1995) Proton transfer reaction mass spectrometry: on-line trace gas analysis at the ppb level. Int J Mass Spectrom Ion Process 149/150:609–619
Lindinger C, Pollien P, Ali S, Yeretzian C, Märk T (2005) Unambiguous identification of volatile organic compounds by proton-transfer reaction mass spectrometry coupled with GC/MS. Anal Chem 77(13):4117–4124
Lindinger C, Labbe D, Pollien P, Rytz A, Juillerat MA, Yeretzian C, Blank I (2008) When machine tastes coffee: instrumental approach to predict the sensory profile of espresso coffee. Anal Chem 80(5):1574–1581
Blake RS, Monks PS, Ellis AM (2009) Proton-transfer reaction mass spectrometry. Chem Rev 109(3):861–896
Hanley L, Zimmermann R (2009) Light and molecular ions: the emergence of vacuum UV single-photon ionization in MS. Anal Chem 81(11):4174–4182
Geissler R, Saraji-Bozorgzad MR, Groêger T, Fendt A, Streibel T, Sklorz M, Krooss BM, Fuhrer K, Gonin M, Kaisersberger E, Denner T, Zimmermann R (2009) Single photon ionization orthogonal acceleration time-of-flight mass spectrometry and resonance enhanced multiphoton ionization time-of-flight mass spectrometry for evolved gas analysis in thermogravimetry: comparative analysis of crude oils. Anal Chem 81(15):6038–6048
Muhlberger F, Hafner K, Kaesdorf S, Ferge T, Zimmermann R (2004) Comprehensive on-line characterization of complex gas mixtures by quasi-simultaneous resonance-enhanced multiphoton ionization, vacuum-UV single-photon ionization, and electron impact ionization in a time-of-flight mass spectrometer: setup and instrument characterization. Anal Chem 76(22):6753–6764
Dorfner R, Ferge T, Yeretzian C, Kettrup A, Zimmermann R (2004) Laser mass spectrometry as on-line sensor for industrial process analysis: process control of coffee roasting. Anal Chem 76(5):1386–1402
Dorfner R, Ferge T, Kettrup A, Zimmermann R, Yeretzian C (2003) Real-time monitoring of 4-vinylguaiacol, guaiacol and phenol during coffee roasting by resonant laser ionisation time-of-flight mass-spectrometry. J Agric Food Chem 51(19):5768–5773
Mühlberger F, Wieser J, Ulrich A, Zimmermann R (2002) Single photon ionization (SPI) via incoherent VUV-excimer light: robust and compact time-of-flight mass spectrometer for on-line, real-time process gas analysis. Anal Chem 74:3790–3801
Dorfner R, Ferge T, Uchimura T, Yeretzian C, Zimmermann R, Kettrup A (2002) Laser/chemical ionisation—mass spectrometry as an on-line analysis technique for monitoring the coffee roasting process. ASIC-19eme Colloque Scientifique International sur le Café, ASIC, Paris
Zimmermann R, Heger HJ, Kettrup A, Boesl U (1997) A mobile resonance-enhanced multiphoton ionization time-of-flight mass spectrometry device for on-line analysis of aromatic pollutants in waste incinerator flue gases: first results. Rapid Commun Mass Spectrom 11(10):1095–1102
Heger HJ, Zimmermann R, Dorfner R, Beckmann M, Griebel H, Kettrup A, Boesl U (1999) On-line emission analysis of polycyclic aromatic hydrocarbons down to pptv concentration levels in the flue gas of an incineration pilot plant with a mobile resonance-enhanced multiphoton ionization time-of-flight mass spectrometer. Anal Chem 71:46–57
Zimmermann R, Heger HJ, Yeretzian C, Nagel H, Boesl U (1996) Application of laser ionization mass spectrometry for on-line monitoring of volatiles in the headspace of food products: roasting and brewing of coffee. Rapid Commun Mass Spectrom 10:1975–1979
Yeretzian C, Jordan A, Badoud R, Lindinger W (2002) From the green bean to the cup of coffee: investigating coffee roasting by on-line monitoring of volatiles. Eur Food Res Technol 214:92–104
Yeretzian C, Jordan A, Brevard H, Lindinger W (2000) On-line monitoring of coffee roasting by proton-transfer-reaction mass-spectrometry. In: Roberts DD, Taylor AJ (eds) ACS Symposium Series 763. ACS, Washington, pp 112–123
Dorfner R, Zimmermann R, Kettrup A, Yeretzian C, Jordan A, Lindinger W (1999) Vergleich zweier massenspektrometrischer Verfahren zur Direktanalyse in der Lebensmittelchemie. Lebensmittelchemie 53:32–34
Friedman JH (1984) A variable span scatterplot smoother. Laboratory for Computational Statistics
Esbensen KH, Guyot D, Westad F, Houmøller LP (2002) Multivariate data analysis: in practice: an introduction to multivariate data analysis and experimental design, 5th edn. CAMO Software AS, Oslo
Kessler W (2007) Multivariate datenanalyse in der bio- und prozessanalytik. Wiley-VCH, Weinheim
We acknowledge Bühler AG for financial support.
Published in the special issue Analytical Sciences in Switzerland with guest editors P. Dittrich, D. Günther, G. Hopfgartner, and R. Zenobi.
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Wieland, F., Gloess, A.N., Keller, M. et al. 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. Anal Bioanal Chem 402, 2531–2543 (2012). https://doi.org/10.1007/s00216-011-5401-9
- Process analysis
- Gas sensors
- Quality assurance/control