The biochemistry and technology of tea manufacture.

This review surveys tea-production technology, chemistry of raw and manufactured tea as well as tea tasting appraisal and chemical analysis of manufactured tea. The paper describes the healthful properties of tea, gives general information on the tea plant and manufactured tea, and presents classification of teas as related to the processing of black green, yellow, and red tea, green pressed tea as well as instant tea and tea dyes. The paper discusses the chemical composition of raw and manufactured tea as well as approaches to the evaluation of tea quality--tea tasting appraisal and chemical analysis. The paper is supplied with the conclusions and references. The section on the healthful properties of tea discusses various aspects of catechin effects--vitamin P, antimicrobial, antioxidative and radioprotective effects. Also described are favorable effects of tea alkaloids--caffeine, theobromine, theophylline that dilatate cerebral vessels and alleviate headaches. The section on the production of different teas (black, green, yellow, red, instant teas, and tea dyes) considers technological methods and biochemical bases of various types of tea manufacture. The role of tea leaf enzymes in the oxidative processes determining the tea quality is discussed in detail. This section also describes the contribution of thermochemical processes into the formation of tea flavor. The compounds dictating tea taste and aroma are discussed, particularly tannins and catechins, volatile oils, nitrogen compounds, and some other substances.