The effect of drying on black tea quality

S.J. Temple, C.M. Temple, A.J.B. van Boxtel, M.N. Clifford

Research output: Contribution to journalArticleAcademicpeer-review

21 Citations (Scopus)


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 fluidized 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.
Original languageEnglish
Pages (from-to)764-772
JournalJournal of the Science of Food and Agriculture
Publication statusPublished - 2001

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