Technology of Tea

Abstract

DR. E. B. HUGHES, past-president of the Society of Public Analysts and Other Analytical Chemists, was unable to deliver his presidential address when he retired from office last year. Accordingly he delivered it after the annual general meeting of the Society held on March I, speaking on "The Technology of Tea". Tea-growing areas are not now confined to Asia; the necessary tropical or subtropical conditions exist elsewhere and tea is now grown extensively in Africa, even so far south as Natal, and also in Russia. In the production of black tea, as distinct from green tea, the main processes are withering, rolling, fermentation and final drying. Withering is a partial natural drying process at as cool a temperature as possible. It dries the leaves to a condition in which they can be rolled and twisted by mechanical action simulating rotatory rubbing between the hands; this damages the cells, whereupon, possibly as a result of 'disorganized respiration', oxidase of the leaf brings about 'fermentation'. This so-called fermentation is mainly oxidation of polyphenols of the leaf to quinone compounds, which readily produce reddish, copper-coloured condensation products. The polyphenols of the leaf are the so-called tea tannins, but they are not tannins in the ordinary sense, as they are not able to convert hide into leather. The rate of 'fermentation' is highly important; if too rapid, it gives inferior products, and the greater rate of fermentation, Combined with lower quality of leaf grown in hot humid conditions, produces a commoner quality of tea. Indeed, the differences in quality and character between teas from different areas are due mainly to differences in geographical and climatic conditions, rather than to varietal differences in the plants grown. Changes in climatic conditions in the, same area may produce much choicer tea at one time than a month earlier or later. It is the practice of blending, dependent on the remarkable skill of the tea taster, that enables the consumer to be supplied with brands of unchanging character. Most good teas, as supplied to the consumer, are blends of more than a dozen lots. Green tea is not subjected, to 'fermentation', the enzyme activity being destroyed by heating the leaf (steaming) as soon as possible after plucking, after which the leaf is rolled and 'fired'.