Effect of loading density on quality of dried teas in fluidized bed drying

Abstract

Loading density is a critical parameter that affects the drying behaviour of teas in a fluidized bed dryer and hence the final product quality. During fermentation process, polyphenols available in teas are converted into theaflavin (TF) and thearubigin (TR). However, the final percentages of TF and TR in teas are determined by the post fermentation reactions which take place within the first few minutes of drying. Effect of high loading densities on quality of dried teas was examined for 27, 29 and 31 kg/m2 against the control of 25kg/m2 using orthodox broken type teas. Quality parameters mainly TF%, TR% and tea tasters score were analysed. An increase in both TF% and TROT ratio was observed in teas dried at higher loading densities but the difference from the control sample was not statistically significant at p=0.05. However, professional tea tasters gave higher scores for overall quality of teas dried at higher loading densities based on infused leaf appearance, liquor colour, liquor strength and liquor quality. Results suggest that loading densities may be increased even up to 31 kg/m2 with a marginal improvement to the overall quality of orthodox broken type teas.