Dehydration of the red chilli (Capsicum annuum L., costeño) using an indirect-type forced convection solar dryer

Chilli is a vegetable that is produced and consumed in various parts of the world, not only for its culinary qualities but also for its nutritional content and potential industrialization. Mexico has the highest genetic diversity of chilli, with more than 40 varieties. A dried chilli has different properties of flavour, colour and pungency and a high added value; however, information about its dehydration is scarce. In this work, the dehydration of a red chilli, the “costeño” (Capsicum annuum L.), which is highly appreciated for its organoleptic properties and used in the food industry, was carried out. The experimental study was performed at the Instituto of Energías Renovables (IER) of the Universidad Nacional Autónoma de México (UNAM) in Temixco, Morelos, México, located at 18°51′NL and 99°14′WL. The drying process was carried out at controlled temperatures of 45°C, 55°C and 65°C, using a laboratory oven and an indirect tunnel-type solar dryer. The drying kinetics between 55°C and 65°C are similar, with drying times of 2.75h and 3.0h, respectively, while at 45°C, the drying time was 6.25h. Wang and Sing’s model gave a better fit for the drying kinetics at 45°C, and the Page model was better for 55°C and 65°C. In the solar drying processes, two ranges of air velocity were established; high velocity was between 1.4 and 2.6m/s, and low velocity was between 0.7 and 1.48m/s. In both cases, a temperature between 31°C and 45°C was obtained. For the first range, the total drying time was 16h, reaching a final moisture content between 0.057kg of water/kg dry matter and 0.90kg water/kg dry matter. For the second range, the time was 21h, with a moisture content of 0.0611kg of water/kg dry matter and 0.109kg of water/kg dry matter.