Heat and Mass Transfer during Drying of Liquid Pasty Plant Extract by Vacuum Belt Drying

The present work is focused on heat and mass transfer during drying of instant coffee within a vacuum belt dryer. A series of drying experiments in a lab-scale dryer were performed. Using an advanced temperature measurement technique, the process could be optimized with respect to product quality. Thermal conductivity of coffee extract was investigated over the whole range from liquid extract to dry product. Additionally, the influence of porosity was analyzed. Based on the results, a numeric model was developed describing the coupled heat and mass transfer. The understanding of the process has been improved and the basis for a strong optimization tool has been found.