The phenolic substances of manufactured tea. IX.—the spectrophotometric evaluation of tea liquors

Abstract Further applications of a spectrophotometric method are described for the determination of polyphenolic oxidation products in black tea liquors for the assessment of quality in tea. In addition to calculating theaflavin and thearubigin contents from optical density measurements at 380 mu, values for total colour and brightness have been calculated from optical density measurements at 460 mu. Confirmation has been obtained that theaflavin content is an extremely important factor in determining quality in black tea, and in determining ‘brightness’ in tea infusions. Thearubigins contribute to colour and strength. The effects of seasonal variations and of methods of manufacture on the composition of tea have been examined. Changes in composition during storage of tea under adverse conditions of temperature and moisture content have been related to losses of quality. The effects of the composition of the water used on the composition and colour of tea infusions are also indicated.