Hygroscopic equilibrium and physical properties evaluation affected by parchment presence of coffee grain

Physical properties are essential for the development of silos, transport calculations, separation and classification of grain and seeds. The present work evaluates the influence of the parchment on the drying and physical properties of coffee grains. The true density (rho(t)), bulk density (rho(b)) and porosity (epsilon) were evaluated for coffee grains (cv. Catuai Amarelo) with and without parchment. Four mathematical models (Chung-Pfost, GAB, Modified Henderson and Oswin) were fitted to the experimental data to acquire desorption isotherms. The drying treatment was conducted in a factorial scheme with four levels of temperature (20, 35, 45 and 55 degrees C) and five levels of relative humidity of the drying air (30, 40, 50, 60 and 80%) in a completely randomized design. The respective equilibrium moisture contents of the coffee grains were measured for each drying condition. No differences were observed among the products on the desorption isotherms. The pulped coffee with parchment (PP) had higher epsilon values than the pulped coffee without parchment (PR). The true density was higher for the PP coffee, but as the moisture content (X) increased, the true densities became more similar for the two samples. The rho(b) was higher for the PP coffee than for the PR coffee. Higher initial and final values of rho(b) were found for the PR and PP coffee, respectively. The Guggenheim-Anderson-de Boer model was the model that best represented the experimental data for the drying process.