The polyphenols, about thirty altogether, account for nearly a third of the soluble matter in the fresh tea leaf. This stimulates the salivary glands, which is why tea is a thirst quencher. The unoxidized polyphenols provide the pungency, while the oxidized ones give the tea its color and flavor. The higher the degree of oxidation, the more color and leaa pungency a tea has. Green tea, which does not undergo oxidation, has more natural unoxidized polyphenols, and also more astringency.
Black tea has more color but less astringency.
Both oxidizied and unoxidized polyphenols may be beneficial. Tea polyphenols, though popularly known as tannins, are not, as widely believed, the tannic acid used in leather preparation. In fact, they are not tannins at all. With some chemical and functional similarity, they became known by this name long before modern methods of chemical analysis made it possible to distinguish the two. Here we have run into another of those name confusions that seem to haunt tea.