Effect of Drying on the Physical Characteristics of Black Leaf Tea

Abstract

The effect of drying process on the physical characteristics of black leaf tea has beeninvestigated. Fermented dhool of black leaf tea was dried using different methods including fluidizedbed, vacuum and microwave drying. Experiments have been carried out to measure the dryingkinetics, relative humidity and exit air temperature during fluidized bed drying. The physicalproperties of the dried product were assessed by moisture content, particle size distribution andaverage particle size. With fluidized bed drying, there are two drying periods for CTC dhool: theconstant drying rate drying period and the falling drying rate period. The drying rate was relativelyfast and depended on the drying temperature. However, with microwave drying, only one dryingperiod for Freedom leaf tea was observed and the drying rate was slower. There is positive linearrelation for CTC dhool but not for Freedom dhool between drying temperature and average particlesize during fluidized bed drying. With vacuum drying and microwave drying, there is positive linearrelation for Freedom dhool between drying temperature, microwave intensity and average particlesize.