The Chemistry of Tea and Tea Manufacturing

Abstract

This chapter covers some of the historical knowledge of tea chemistry and tea manufacture, but, more importantly, brings together the body of current chemical research on tea. A tea leaf is subjected to one of three major processing methods—fermenting, steaming, or partial fermenting—to produce black, green, or oolong tea. The chapter outlines the manufacturing process of black tea that applies only to northeast India. It deals with the chemical constituents present in fresh green tea leaves before processing. All major conversions of chemical constituents from tea leaf to manufactured tea have been discussed specifically. Attempts have been made to study the chemical composition of parts of tea plant other than leaves. The chapter discusses changes in composition of black tea during manufacturing. Flavor in tea is a rather loose term in that it depends, among other things, on the type of tea that is, fermented black, semi-fermented oolong type, or unfermented green tea. Furthermore, it varies as to the source of manufacture. As one of the goals in discussion of the chemical constituents of tea is to link to the quality of tea by means of some objective testing method, it examines in some detail the procedure of a subjective evaluation. Some attempts have been made in assessing the chemical basis of quality and to evolve objective methods of evaluating tea. Conventional methods of manufacture, particularly in northeast India, have been replaced to some extent by other methods in which the leaf receives a more thorough bruising, resulting in a quicker and more extensive fermentation.