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

The flavour of a freshly prepared cup of coffee is the final expression of a long chain of transformations. Along this journey from the seed to the cup, roasting is without doubt the most significant processing step. Here we report on the development of a fast on-line process control technology for a consistent roast, batch after batch. It involves the on-line monitoring of the roaster off-gas using Proton-Transfer-Reaction Time-of-Flight Mass-Spectrometry (PTR-ToF-MS) and the analysis of the mass spectral profiles via principle component analysis (PCA). This allows predicting the roast degree in real time. The PCA was calibrated in advance with a large number of roasting trials, to develop the predictive model. The 3D space of the three first principal components allows to predict in real time the roast degree, based on PTR-ToF-MS profiles of the roast gas. This work demonstrates that time resolved analysis of roaster off-gas provides a detailed picture of the evolution of the roasting process