The aim of this study was to develop a soft sensor for estimation of the solids temperature and moisture content during the drying of porous alumina in a spouted bed. Mechanistic-empirical and fundamental models were employed to develop the soft sensors, which were evaluated for continuous and intermittent drying. Soft sensors provided consistent results and good agreement with experimental measurements. The robustness of the soft sensor also was confirmed, since it was able to predict the solids moisture content during intermittent drying based on a calibration from the continuous process. Therefore, this work describes the successful development of a reliable, robust, and low computing cost mathematical model soft sensor.