Batch-Scale Simulation of Heat and Mass Transfer of Coffee Roasting in Spouted Bed Roasters

Understanding heat and mass transfer phenomena is fundamental to successful roasting practices. These phenomena can be quantified via an energy balance over the roaster, whereby heat and mass transfer equations can be formulated. Through rigorous calibration of the simulation with experimentally derived data obtained using a spouted bed roaster, a zero-dimensional, batch-scale model of coffee roasting was developed to predict time–temperature roasting profiles. Calibration involved implementation of (i) an airflow calibration to determine the air mass flow rate and velocity of air input to the roaster, (ii) kinetic models and empirical correlations to describe coffee’s physicochemical development during roasting and (iii) a non-linear least squares fitting procedure to estimate system-dependent parameters—such as the thermal response coefficient and heat transfer effectiveness—that are otherwise difficult to determine. In this way, user inputs of roasting parameters relevant for spouted bed roasters—batch size, airflow and inlet air temperature—were probed to capture the full kinetics of coffee roasting under various process conditions, from which rate constants for mass loss kinetics were determined. In this study, development of the zero-dimensional, batch-scale simulation is described, alongside rigorous calibration with pilot-scale roasting trials. These simulations are application-ready and can be used by product and process developers to roast coffee in silico, providing not just an informative tool, but one that can be instructive and predict requirements for raw material (green coffee) properties, roasting process conditions, or roasted coffee properties.