Tóm tắt
AbstractThe formation of a deposit, known in the tea trade as tea ‘cream’, when a black tea infusion ‘creams down’ on cooling is used by professional tea tasters as an indication of strength and briskness in the infusion. This ‘cream’ is essentially a complex of caffeine with theaflavins and thearubigins (polyphenol oxidation products that have been identified in soluble constituents of black tea). The amount and composition of the ‘cream’ formed depends on the composition of the tea and the strength of the infusion. A precipitate containing the same constituents as tea ‘cream’ is formed when 1% by volume of conc, sulphuric acid is added to a tea infusion, and the amount of polyphenolic material in this precipitate—estimated by titration with alkaline permanganate (‘cream index’)—provides a measure of the ability of a tea infusion to cream down. Support has been obtained for the view that ‘briskness’ in a tea infusion, which is negatively correlated with the ‘cream index’, is due to a caffeine theaflavin complex. The colour of the cream, which may vary from orange to brown, is determined by the ratio of thearubigins to theaflavins. A visual assessment of the amount and colour of the cream formed in a tea infusion by a tea taster is therefore in effect a judgment of the amounts and relative proportions of theaflavins, thearubigins and caffeine in the tea, as an indication of the qualities of the tea.
