Drying Kinetics of Red Chillies in a Rotary Dryer

Drying kinetics of red chillies in a rotary dryer was determined within a temperature range of 50-65 °C. The time required to dry 10·5 kg chillies (loaded to 75% of dryer volume) from an initial moisture content of around 330% dry basis (db) to the final moisture content of around 10·5% db was 32,27,23 and 20 h at 50, 55, 60 and 65 °C of drying air temperature, respectively. The average capsaicin content and value for the red/green chromaticity coordinate a* of dried chillies decreased from 0·54% to 0·28% and 22·83 to 12·31, respectively, as the drying air temperature increased from 50 to 65 °C. The overall performance of the chillies dried at 55 °C was the best, when the quality attributes viz., drying time, capsacin content and red colour, were considered. Suitable models are identified to predict the moisture ratio of chillies at different drying air temperature of a rotary dryer. The effective moisture diffusivity Deff of chillies increased from 13·635 to 19·949 mm2 h−1 as the drying air temperature of a rotary dryer increased from 50 to 65 °C. The activation energy of diffusion Ea was calculated as 24·476 MJ kg mol−1.