The effect of drying on black tea quality

Abstract

Drying is an important part of tea manufacture, where enzyme reactions in earlier phases are terminated by heat and moisture loss, and new compounds are produced by the action of heat. This work is an attempt to quantify the temperatures required to produce the desired changes without damage through exposure to excess heat. Experiments were carried out giving already-dried tea further heat exposure, drying tea from wet dhool in a thin layer, and drying a larger sample in a batch uidized bed dryer. Temperatures in the range of 60±140°C were used. Effects were monitored by commercial tasters, thin layer chromatography, reverse phase HPLC and size exclusion HPLC. Exposure to at least 80°C was found to be necessary for quality development. For periods of less than 1 min, tea particle temperatures of up to 120°C may be tolerated, but, in general, temperatures of 110°C and above may be considered deleterious. Inlet air temperatures may be in excess of these values, but only while drying rates are high. The stewing phenomenon, cited by several authors, could not be found when drying times of less than 15 min were used.

Application of response surface methodology to optimize the drying condition of black tea using superheated steam dryer

“…However, a prolonged exposure of heat can result in loss of TPC. A similar trend was observed in a study carried out by Temple, Temple, van Boxtel, and Clifford (2001) that proved rapid drying is vital to prevent the loss of TPC.…”

Chemical characterisation of CTC black tea of northeast India: correlation of quality parameters with tea tasters' evaluation

“…Although many of the basic relationships of black tea quality with chemical composition and other variables of plant tissue remain unknown, several attempts have been made to establish the relationships of biochemical components, process variables, genetic factors, fertiliser use and various environmental factors with black tea quality 3, 7, 36–39. In this endeavour, attempts have been made to determine the environmental effect on biochemical components of three specific regions of northeast India, namely Brahmaputra valley, Barak valley and Dooars region.…”

Identification, quantification and availability of carotenoids and chlorophylls in fruit, herb and medicinal teas

“…Convection dryers and other hot air methods are commonly used by tea producers (Raghavan and Orsat, 2007). Moreover, temperatures used while drying caused the decomposition of various compounds (Mahanom et al, 1999;Temple et al, 2001). Unfortunately, none of the tea companies contacted replied concerning the methods used for drying their teas, so it is not possible to correlate the type of drying with the overall effects on pigment stabilities and levels.…”