The chemistry of Tea The chemical profile that determines the distinct tea character. The chemical composition of fresh tea leaves and processed green tea are very similar. Green tea contains the organic compound polyphenols, commonly known as catechins, which mostly include flavanols, but also contain flavandiols, flavonoids, and phenolic acids. The main process responsible for the chemical changes of tea is oxidation; oxidation is the process of polyphenol oxidase-dependent oxidative polymerization. Due to tea processing the chemical composition of black tea and fresh tea leaves are much different. Black tea contains bisflavanols, theaflavins, thearubigins, and other oligomers. The theaflavin is significant to the character of black tea. Theaflavins, which give the characteristic color and taste to black tea. Thearubigens, which are even more extensively oxidized and polymerized, have a wide range of molecular weights, and are less well characterized. Oolong tea, a partially oxidiz