Moisture Diffusivity, Shrinkage, and Apparent Density Variation During Drying of Leaves at High Temperatures

The variation of moisture diffusivity, apparent density, and shrinkage during drying of yerba maté leaves at high temperatures were studied. A simple mathematical model that describes the variation of the temperature and moisture content into the leaf during drying was developed. Temperatures of air varied between 100 and 130°C when the experiments were carried out in a convective cross-flow air dryer. Thickness and apparent density varied greatly with moisture content, but this variation does not depend on drying temperature. Moisture diffusivity varied from 2.3 × 10−11 to 2.5 × 10−10 m2/s, and activation energy values are in the range of other foodstuffs. A great dependence of moisture diffusivity on moisture content was also found.