Fermented teas belong to the category dark tea, or hei cha in Chinese. This is kind of tea is stored and aged, during which a fermentation process will give the tea a unique and earthy flavour.
Dark teas are produced in China. The best known kind is called pu’er and come from the Yunnan province. Dark teas are also produced in many other Chinese provinces, such as Guangdong, Hubei, Hunan, Jiangxi and Sichuan.