- D. K. Pratihar
- Narosa Publishing House, New Delhi.
Vacuum drying process could be used for drying of black CTC or orthodox tea for better quality. The level of vacuum was maintained at 28.5 inch ofHg inside the vacuum chamber. The drying parameters, such as, plate temperature during drying, the loading rate of dry solid on the plate and duration of drying were varied on the basis of Rotatable Central Composite Design (RCCD). From preliminary experiments, the ranges for drying temperature, loading rate and duration were fixed as 60 to tOO'C, 0.2 to 0.35 kg dry solid/m2 and 20 to 45 min; respectively. Moisture content ofthe product and liquor colour values (brightness, redness and yellowness) was measured. The independent parameters were optimized on the basis ofthe desired values ofthe quality parameters of product, using Design Expert Software. The optimized values ofthe drying parameters were obtained to get moisture content of product within 3 to 4% (wet basis), maximum redness and yellowness value and the brightness value closest to the ECP dried tea. The optimized alues ofthe independent drying parameters, viz. plate temperature, loading rate and duration were 88.9'(" 0.212 kg dry solid/m2 and 42 min respectively.