Numerical modeling of heat and mass transfer during coffee roasting process

In this work a numerical model, based on a 3D 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. Two domain geometries were tested: one simplified, based on a simple semi-ellipsis, and one made acquiring the shape of an Arabica coffee bean using a 3D scanner. 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 5.97/C176C). Similarly, the calculated volume averaged moisture was in good agreement with the experimental data (RMSE 264.251 mol/m3) over the entire time span. This model can be useful to optimise the roasting process control.