Innovative process for drying of parchment coffee: combined fluidized-microwave technology

Abstract

In the present work, the fluidized bed drying process combined with microwaves was applied to Parchment Coffee. Experiments were carried out in experimental laboratory equipment consisting with a nominal power of 700 W and 2450 MHz of frequency. The equipment includes a centrifugal blower that provides different air velocities to generate the fluidization. A hot wire anemometer was used to measure the inlet air velocity and temperature. The moisture content and surface temperatures of samples were recorded at 5 min time intervals during the drying process. The process was carried out until the grains reached the final moisture level between 10 and 12% (wb). The experimental design corresponds to 3 levels of microwave power (0, 30 and 50%) and different air velocities (0, 1.6 and 3.2 m/s) at room temperature. Drying curves were obtained for each operating conditions. All measurements were carried out in triplicate. The experimental curves showed that the drying rate increased with air velocity and microwave power. At each drying condition, various models (Newton, Logarithmic, Midilli-Kucuk) were used to describe the coffee behaviour. In all cases, the statistical parameter estimations showed that R2, χ2 and RMSE values ranged from 0.948 to 0.999, 2 10-5 to 0.004, and 0.0029 to 0.0628, respectively. Based on the statistical analysis a good agreement was achieved for all empirical models.