Roasting, Grinding, and Storage Impact on Thermodynamic Properties and Adsorption Isotherms of Arabica Coffee

Abstract

This work aimed to evaluate alterations on the water sorption of coffee due to roast, grind, and storage. Crude grain coffee (Coffea arabica) was roasted at two levels: medium light and moderately dark. Grain was grinded in fine (0.59 mm), medium (0.84 mm), and coarse (1.19 mm) particle sizes, besides the whole coffee lot. Samples were then stored at polypropylene bags and kept at biochemical oxygen demand type chambers in two storage temperatures (10 and 30C). These were analyzed at 0, 30, 60, 120, and 180 days, regarding water content and water activity. Mathematical modeling and thermodynamic properties of coffee moisture adsorption process were accomplished. It was concluded that particle size did not significantly affect water content of coffee, independently of roast degree. Sigma-Copace model best represented hygroscopic equilibrium of roasted coffee. Water content reduction increases the differential enthalpy and entropy of sorption and Gibbs free energy. Practical Applications Commercialization of crude grain coffee, soluble coffee, roasted, and grinded coffee, among others (extract, essences, and concentrated) represents 9.2% of Brazilian exportation. Higher distances lead to physical, chemical, and microbiological changes in agricultural products. This trend could cause the deterioration of food products. Information on the sorption characteristics of roasted and grinded coffee could not be found in the literature, regardless of this culture importance. Sorption isotherms data are key information to predict optimum storage and trading conditions to ensure quality. Finally, the lack of quality may affect employees, entrepreneurs, and other professionals that works with coffee. This article presents the adsorption isotherms and thermodynamic properties of roasted and grinded coffee (Coffea arabica L.).