DRYING SPEED OF COFFEE BEANS IN A ZENITHAL SOLAR DRYER IN THE CAÑADA REGION, OAXACA, SPAIN

A zenithal type solar dryer was evaluated during two drying cycles: the first cycle was under a humid environmental condition (rainy and cloudy days), the second cycle under a dry condition (sunny and clear days).The temperature and humidity of the air inside and outside the solar dryer were compared by recording these parameters every 20 minutes to determine the influence of these conditions on the coffee bean drying process.The results indicated that the maximum temperature difference between the inside and outside of the dryer was 17.7 C (humid cycle) and 18.0 C (dry cycle).Temperatures of up to 48.5 C were recorded in the humid cycle and 47.4 C in the dry cycle, which can be dangerous for the coffee beans, since, when exceeding 45C, they can damage the embryo causing undesirable flavors in the organoleptic analysis.Based on the bean drying curves, the solar dryer evaluated does not accelerate the drying process, but it favors a loss of humidity at a homogeneous rate in comparison with traditional drying, which presents strong fluctuations in the humidity of the bean.