Numerical model of heat and mass transfer during roasting coffee using 3D digitised geometry

Nowadays roasters are equipped with electric control board, thermo-regulator device, display for temperatures and on-line sensors to detect defects and/or the roasting end, depending on coffee types and blends and the desired roasting degree. It is important to have a good control of the roasting process in order to obtain a high quality final beverage. In this work a numerical model, based on a 3D digitized geometry, able to describe the heat and moisture transfer inside a coffee bean during the roasting process, was developed. The model makes reference to a rotating cylinder roaster in natural convection conditions. For the multiphysics model development heat and mass transfer equations inside the coffee bean were numerically solved using a finite element technique. To validate the numerical model, green coffee bean was singularly roasted using a rotating drum roasters prototype. The calculated moisture concentration and time-temperature curves were then compared with the observed data. The calculated temperature values, in the centre of the bean, appear to be in good agreement with those measured inserting thermocouples into the coffee bean (RMSE 6°C). Similarly the calculated volume averaged moisture was in good agreement with the experimental data (RMSE 265 mol/m 3) over the entire time span. This model can be useful to optimise the roasting process control.