Abstract
<p>Drying is a fundamental step in post-harvest handling of coffee because moisture content at the end of drying affects several important aspects, such as sensory quality, storability, and color. Within this context, the aim of this study is to determine water distribution within the natural coffee fruit during and at the end of the drying process. For that purpose, simulations were made through finite elements using computational fluid dynamics. Experimental data on moisture content of coffee fruitin the “cherry” stage were collected during drying, which was carried out at a temperature of 40°C and relative humidity of 25% to 0.18 decimal(dry basis – d.b.)to compare the results of the experiment with the results of the simulations. Ten mathematical models of the drying process were developed for the collected data. The two-term exponential model best fit the data. The results of the simulations in computational fluid dynamics were compared to the results from experimental drying, and a satisfactory fit was obtained. The effective diffusivity coefficient (D<sub>eff</sub>) was developed for the model, obtaining the value of 2.87 x 10<sup>‑11</sup> m<sup>2</sup> s<sup>-1</sup>. At the end of drying, the model exhibited 57.1% of the projection area of the coffee fruit with moisture content below 0.18 decimal (d.b.). Thus, the model can be used for other applications.</p>
Highlights
Coffee has a prominent position in Brazilian grain production, with 349,9 million dollars in exports, according to the Informe Estatístico do Café (2018).The drying stage is fundamental in coffee to prevent the growth of microorganisms and fermentations that can compromise the quality of newly-harvested coffee, which has high moisture content and uneven maturity of the coffee fruit (RESENDE et al, 2009)
During the process of drying agricultural products, conditions are considered isothermal, and water transfer is restricted to the surface of the product (Bergman, et al 2011).the aim of this study was to determine the distribution of moisture content within natural coffee fruit during and at the end of the drying process
The moisture content of the coffee fruit was determined by the standard method of ISO 6673 (INTERNATIONAL ORGANIZATION for STANDARDIZATION ISO, 2003)
Summary
Coffee has a prominent position in Brazilian grain production, with 349,9 million dollars in exports, according to the Informe Estatístico do Café (2018).The drying stage is fundamental in coffee to prevent the growth of microorganisms and fermentations that can compromise the quality of newly-harvested coffee, which has high moisture content and uneven maturity of the coffee fruit (berries) (RESENDE et al, 2009). Coffee has a prominent position in Brazilian grain production, with 349,9 million dollars in exports, according to the Informe Estatístico do Café (2018). The temperature of the coffee fruit must be strictly controlled because an excessive increase in temperature greatly affects its quality. Coffee should be dried at a temperature of 40°C for this operation not to affect beverage aroma and flavor (BORÉM, 2008). Air flow during coffee drying has an effect only at the beginning of drying (Burmester; Eggers, 2010). In drying coffee fruit at low relative humidity, an increase in temperature brings about an increase in the effective diffusivity coefficient (Deff), which ranges from 1.908 to 3.721 x 10-11 m2 s-1, as well as in drying rate (Alves, et al 2013)
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