Perfil de temperatura e teor de água e riscos microbiológicos da secagem de café natural em camada fixa com e sem inversão do fluxo de ar

Abstract

Coffee drying through fixed layer dryers has been widely used by Brazilian coffee growers. However, high water content gradients formed in these dryers are often reported, as well as the appearance of microorganisms in the coffee mass. In view of the need for adaptation to these conventional dryers, natural coffee drying was monitored using periodic drying airflow reversal to minimize these commonly encountered problems. The present work was developed in order to monitor the performance of these dryers and their effect on the quality of the final product, comparing to an adaptation made in conventional fixed layer dryers. The experimental stage consisted of analyzes made during and after the drying process, which began with one meter of coffee layer (15,000 L). During drying, the following characteristics were monitored at various points in the drying chamber: temperature of drying air, intergranular air, exhaust air, and ambient air; relative humidity of drying air, ambient air, and exhaust air and water content of the product at different heights in the drying chamber (0,12; 0,36 e 0,60 m). Among the dry product evaluations, color analysis, percentage of black-green defect and microbiological analysis were performed. According to the results obtained, air flow reversal drying resulted in a moisture content gradient of 0.4% (w.b.), whereas conventional drying caused a gradient of 8% (w.b.). Regarding the color of the product in the different drying managements, air flow reversion resulted in lighter products. For the black-green defect analysis, it was observed a higher incidence of defect in the lower layer of conventional drying than in drying with air flow reversal. For microbiological analysis, were found fungi of genera Cladosporium and Fusarium and section Circumdati, among others. The average incidence of these fungi was higher in conventional drying than in airflow reversal drying.