Coffee cherries drying process and the influence of environment relative humidity in the mathematical modeling, moisture content, and enthalpy of vaporization

Abstract

The drying operation is one of the most important stages of the coffee production. Thus, we aimed to evaluate the influence of the ambient relative humidity (40, 50 and 60%) in the natural process of coffee (Coffea Arabica L.) drying at different air temperatures (23 °C, 40 °C and 60 °C) using mathematical modeling, equilibrium moisture content, and enthalpy of vaporization. Coffee cherries natural processed and dried with a drier of fixed layer was used. The study was conducted at the Department of Engineering and Technology Center of Post-Harvest Café, of the Federal University of Lavras. The results showed that the equilibrium water content of the coffee cherry is directly proportional to the water activity, and decreased increasing temperature during the same water activity. The Oswin model showed the best fit to describe the phenomenon of hygroscopicity of the coffee cherry. The latent heat of desorption increased decreasing the water content and decreased increasing temperatures of the same water content. In addition, the Midilli model showed the best fit to the drying data. Furthermore, the Gibbs free energy increased increasing temperature, it’s their magnitude being was positive in the temperature range used in this study. In conclusion, the different ambient relative humidities did not significantly influenced the processes of drying coffee cherries.