Validation and Improvement of Heat and Mass Transfer Model in Predicting the Coffee Roasting Profile

Abstract

Abstract-Evolution of a cup of coffee consist of 24 steps, with roasting as one of the most important steps since it establishes the organoleptic properties of coffee. The coffee roasting process is an exothermic reaction, characterised by a change in colour, aroma, expansion and crack of the green coffee beans. In this study, heat transfer parameters that play a role in the coffee roasting process and roasting profile were investigated. Ten models were developed and published up to date to predict the coffee bean roasting profile, and all of the investigations on this topic use heat and mass transfer parameters as constants given by reference [7]. The aim of this study is to evaluate the heat transfer parameters; air to bean heat transfer coefficient, specific heat capacity of the bean and thermal conductivity of the bean, and validate an improved model that predicts the roasting profile. The roasting profiles were investigated with four different roasting temperatures, i.e. 170 ºC, 190ºC, 210ºC and 230ºC. MATLAB® Simulink was used to simulate Schwartzberg"s model to estimate the coffee roasting profile. The effect of heat transfer parameters on the roasting profile was investigated and the roasting profile predicted by the model was validated with experimental data. The model was then improved by varying the specific heat capacity of the bean, thermal conductivity of the bean and heat transfer coefficient. It was found that the effect of thermal conductivity of the bean on the roasting profile is very small and therefore negligible. Increasing the specific heat of the bean or decreasing the heat transfer coefficient decreases the mean squared error between predicted roasting profile and experimental roasting profile.