A Kinetics and Modeling Study of Coffee Roasting Under Isothermal Conditions

In this study, changes in lightness, roast loss, residual CO2, and total volatiles of an Arabica coffee were investigated under isothermal conditions at 220, 230, 240, and 250 °C. The lightness of the roasted coffee, expressed as L* value, followed two-stage processes that could be modeled using pseudo first-order reaction models, giving activation energies of 59.7 and 170.2 kJ/mol for the first and second stages, respectively. Roast loss data also exhibited two-stage behavior, but followed zero-order reaction kinetics, with activation energies of 52.9 and 181.3 kJ/mol for the first and second stage, respectively. The first-to-second stage transition for L* value and roast loss occurred at light-medium roast. Residual CO2 in the coffee beans correlated negatively with L* value below medium-dark roast degree. However, a reversed correlation was observed above dark roast degree. The volatile compounds generated in roasted coffee were highly dependent on roasting temperature and roast degree.