Yunnan Pu’erh is a fermented tea. The tea undergoes a process called microbial fermentation, in which the leaves are exposed to open air. The humidity and oxygen cause the tea to oxidize, changing the flavor. The longer the tea oxidizes, the darker the leaves become. This is why some refer to Pu’erh teas as “dark tea” not to be confused with black tea (we also have Yunnan black tea). Fermentation reduces astringency and improves after-taste. Fermentation can also produce metabolites that are known to have digestive health benefits.