The influence of hot-air mechanical drying on the sensory quality of specialty Colombian coffee

Abstract

The main aim of this study was to evaluate the impact of mechanical drying on the sensory quality of specialty coffee produced on three Colombian coffee farms. The technique involved a study of the coffee bean drying process parameters, such as temperature (35, 45 and 55 ℃), airflow (100 m3/min∙m2) and thickness (0.2 m) for mechanical drying, vs conventional drying in the open sun until 11% of moisture content was reached. For mechanical drying, the effective diffusion coefficient, electrical conductivity and drying kinetics were evaluated. A sensory test was performed for three storage periods (3, 6 and 9 months) using the Specialty Coffee Association (SCA) protocol. The results showed that the effective diffusion coefficient varied from 3.21 to 8.02 × 10−7 m2/s for mechanical drying and from 4.21 × 10−11 m2/s for drying in the open sun. The time drying time was established at 20.35 ± 0.06, 29.10 ± 0.09 and 71.52 ± 0.11 hours for mechanical drying at 55 ℃, 45 ℃ and 35 ℃ respectively and 54.48 ± 11.37 hours for drying in the open sun system. The average moisture content at the end of all drying operations was 12.5%. Electrical conductivity rose from 11.71 to 16.86 µS/cm∙g at drying temperatures ranging from 35 to 55 ℃. The sensory test revealed that storage duration had no effect on the quality of the coffee drink when in touch with the drying process, with mechanical drying yielding higher sensory ratings. The coffee beans were dried at 55 ℃, yielding coffee samples with SCA scores more than 85 points. In overall, it is determined that the convective mechanical drying method is a viable approach for the processing of specialty coffee beans since it allows for the retention of high-quality sensory qualities, allowing it to command higher market pricing.