The aim of the study was to describe the drying kinetics of washed coffee (Coffea arabica L.) and evaluate the best mathematical model to fit the experimental drying data conducted with different air humidity (40 %, 50 %, and 60 %) and temperatures (23 °C, 40 °C, and 60 °C). The fruit shakes were standardized washing, separation, and manual selection of green coffees, pass cane, and green buoy. Then, approx. 150 L of coffee cherries were pulped and taken directly to the yard. Drying the washed coffee was completed in a mechanical dryer and yard. The obtained results showed that the different conditions of the ambient air significantly influenced the processes of drying pulped coffee. The water content of the hygroscopic equilibrium of pulped coffee is directly proportional to the water activity and relative humidity, decreasing with increasing temperature, for the same value of equilibrium relative humidity. The Oswin model was best represented by the hygroscopicity of the pulped coffee, while the Midilli model shows the best fit to describe the drying curves of the washed coffee. The effective diffusion coefficient increases with increasing temperature of the drying air and reducing of relative humidity, being described by the Arrhenius equation PALAVRAS-CHAVE: Drying. Mathematical Modeling. Pulped Coffee.R. bras. Tecnol. Agroindustr., Ponta Grossa, v. 11, n. 2: p. 2397-2419, jul./dez. 2017.
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INTRODUCTIONThere are several factors that influence the final quality of the coffee, as soil and climate characteristics, cultivars, driving and crop management, harvesting, processing, drying, and storage. There are various forms of processing that result in major differences in the sensory attributes and there are common reports of superiority to coffee peeled and pulped and in relation to natural coffee. Drying is one of the most important stages in the processing of coffee, both from the standpoint of energy consumption and the influence this has on the operation quality of the final product.Given these problems, we seek greater control of the drying parameters (temperature of the drying air temperature of the grain mass, relative humidity, and air flow) in order to minimize adverse situations to the product. On the other hand, if the best drying techniques are not used, the quality may be impaired as a result of physical, chemical, and sensory (BORÉM et al., 2008;SAATH et al., 2010). The drying of agricultural products, thin layer, has the purpose of determining the rates of drying of the product using for data collection recording the mass loss occurred in a sample during water removal (RESENDE et al., 2009).Thus, the drying curves, thin layer, vary with species, variety, environmental conditions, methods staging post-harvest, among other factors. Accordingly, various mathematical models have been used to describe the drying of agricultural produce, although in most cases, the semi-empirical relationships and empirical have been shown to predict the best options for the drying of grains and seeds, altho...