The foam mat drying of yacon juice (YJ) and concentrate yacon juice (CYJ) was conducted under various conditions of thickness of product (0.5, 1.0 and 1.5 cm) and air temperature (50, 60 and 70 degrees C). After drying the resulted dry powder was removed from the metallic tray and pulverized. Layer thickness and air temperature influenced statistically (p > 0.5) drying time, moisture content and water activity (Aw) of the product. The shortest drying time to reach the desired Aw (0.1-0.3) corresponds to the condition of 0.5 cm and 70 degrees C for both juices - 59 and 65 min for the YJ and CYJ, respectively. The process was modeled in terms of heat and mass transfer and then simulated by a finite element method software. The model was able to predict the process satisfactorily and the foam drying technique allowed to obtain yacon powder of good quality, which can be inserted in various food formulations. (C) 2015 Elsevier Ltd. All rights reserved.