Thin-layer modeling for drying of pressed tea leaf residue to produce green tea

A novel technique was developed for the production of instant green tea powder from the juice expressed out of fresh tea shoots. The pressed leaf residue can be further processed to green tea granules by hot air drying. The present study was carried out to determine the drying characteristics of pressed tea leaf residue in a recirculatory convective air dryer (air temperature 45-55 degrees C, sample thickness 3-5 min and air flow velocity 1.5-2.5 m/sec). The drying data were fitted to different semi-theoretical models of which Page model gave better predictions than other models and satisfactorily described the thin-layer drying characteristics of pressed tea leaf residue. The effective diffusivity varied from 2.722 x 10(-10) to 6.813 x 10(-10) m(2)/sec over the experimental temperature range and a second order polynomial relationship between InMR and drying time (t) was developed. An Arrhenius type equation was developed to express the temperature and thickness dependence of effective moisture diffusivity.