Teas divide into three groups according to the method used in preparing them for market.

Unoxidized or Unfermented - These include the green teas, an example of which would be the Japan pan-dried tea. The leaves are greenish and the tea made from them is light colored and delicate in flavor.

Partly Oxidized or Partly Fermented - These include the Oolong and Ceylon varieties. The leaves are brown and the tea made from them is darker in color than that made from the unfermented leaves and has a characteristic aromatic flavor.

Oxidized or Fermented - These are known as black teas, such as English Breakfast or China Congou, and India teas such as Darjeeling and Pekoe. The leaves are black and the beverage has a rich dark color and a fruit flavor.

During oxidation or fermentation, chemical changes take place which improve the flavor and reduce the amount of tannin, the substance which gives tea its astringency. As green teas are not oxidized, they contain a larger proportion of tannin than the others and consequently have a more astringent flavor.