The second important chemical compound present in tea is caffeine. It is an alkaloid (1, 3, 7-trimethyle xanthene) of the purine group, a colourless compound with slightly bitter taste and has a stimulating effect, both physical and mental, on human being. Caffeine content of tea leaves varies from 2 to 5 percent depending upon the cultivar and climatic conditions. Caffeine is a major purine responsible for the taste, briskness and stimulating effect of tea. What do you mean by briskness? Briskness is a live tase as opposed to flatness or softness. Fresh spring wate may be described as brisk compared with cold boiled water.