Effect of blanching and air flow rate on turmeric drying

Turmeric processing involves two main steps, blanching and drying. Blanching is a common step in the traditional processing of rhizomes, and hot air drying is an alternative to traditional solar drying. For this study, drying kinetics were performed at different air flow rates (0.2, 0.5, 0.7, 1.2, 2.1, 2.6, 3 and 4 m/s) to determine the effect of air flow on the process. To examine the blanching effect, drying kinetics were carried out with blanched and unblanched rhizomes at different temperatures (60, 70, 80, 90 and 100 degrees C). A diffusion model and two empirical models (Weibull and Peleg) were used to describe mass transfer during drying. The effect of air flow rate on external resistance was observed, and the air velocity transition zone between the external and internal resistance control zone was identified (1-2m/s). Blanching previous to drying increased the process rate at all the temperatures tested, although its effect was reduced when the air drying temperature increased. Empirical models fitted better drying kinetics than the diffusion model, however, the diffusion model provides valuable information about the phenomenon of water removal and scaling up.