Green Tea
TEA
Dr. B.L. Wedzicha of t h e Procter D e p a r t m e n t of Food Science, U n i v e r s i t y of Leeds, describes t h e c h e m i s t r y of black t e a manufacture Tea is the m o s t w i d e l y c o n s u m e d beverage in the w o r l d . The economic importance of an annual w o r l d production of tea estimated to be in the region of 1-1·5 million tonnes has resulted in considerable attention being paid to the understanding of the chemical and physical changes w h i c h take place during tea manufacture. The three main types of tea, black, green and instant tea, are made by processing the y o u n g shoot or flush, comprising the terminal b u d and t w o adjacent leaves of the tea plant (Camellia sinesis), s h o w n opposite. Of these types of processed tea the most important is the familiar black tea, w h i c h is a fermented product, the colouring matter arising f r o m enzymic oxidation of phenolic components of the tea leaf. Green tea, o n the other hand, resembles m o r e closely the dehydrated leaf, any chemical changes being non-enzymic and its brews do not contain highly coloured products. Green tea is the m o s t popular f o r m of tea in a number of countries including China and Japan. Instant tea may be prepared f r o m both black and green tea, the process essentially involving extraction w i t h water, concentration and dehydration. The w o r l d market for instant tea, however, is small (some 5% of w o r l d tea production), indicating perhaps that satisfactory products have not yet reached the customer. The market has been further affected by the introduction of tea bags. In view of the commercial importance of black tea and the intricacy of the mechanisms of its manufacture, this product has received by far the most attention and the purpose of the present article is to outline some findings in this field. The black tea process 1 The freshly plucked tea flush is allowed to wither in air for some 18-20 hours, or for shorter periods when heated
Dr. B.L. Wedzicha of t h e Procter D e p a r t m e n t of Food Science, U n i v e r s i t y of Leeds, describes t h e c h e m i s t r y of black t e a manufacture Tea is the m o s t w i d e l y c o n s u m e d beverage in the w o r l d . The economic importance of an annual w o r l d production of tea estimated to be in the region of 1-1·5 million tonnes has resulted in considerable attention being paid to the understanding of the chemical and physical changes w h i c h take place during tea manufacture. The three main types of tea, black, green and instant tea, are made by processing the y o u n g shoot or flush, comprising the terminal b u d and t w o adjacent leaves of the tea plant (Camellia sinesis), s h o w n opposite. Of these types of processed tea the most important is the familiar black tea, w h i c h is a fermented product, the colouring matter arising f r o m enzymic oxidation of phenolic components of the tea leaf. Green tea, o n the other hand, resembles m o r e closely the dehydrated leaf, any chemical changes being non-enzymic and its brews do not contain highly coloured products. Green tea is the m o s t popular f o r m of tea in a number of countries including China and Japan. Instant tea may be prepared f r o m both black and green tea, the process essentially involving extraction w i t h water, concentration and dehydration. The w o r l d market for instant tea, however, is small (some 5% of w o r l d tea production), indicating perhaps that satisfactory products have not yet reached the customer. The market has been further affected by the introduction of tea bags. In view of the commercial importance of black tea and the intricacy of the mechanisms of its manufacture, this product has received by far the most attention and the purpose of the present article is to outline some findings in this field. The black tea process 1 The freshly plucked tea flush is allowed to wither in air for some 18-20 hours, or for shorter periods when heated
References: 2,3,4 and 7 are reviews and are ideal for further reading. The reader should, however, note that some structures shown in the earlier publications were amended as a result of further experimental work. Other suggestions for further reading are: M.A Bokuchava and N.I. Skoboleva, Adv. Fd Res., 1969,17,215; and E.A.H. Roberts in The Chemistry of Flavanoid Substances, Pergamon, 1962, pp468-512. Nutrition and Food Science RCHO + CO2 + NH 3 where R is an alkyl group and this 4