Fermentation in tea refers to the breakdown of substances found in the leaves by bacteria, yeasts, or other microorganisms. Pu’er is not synonymous with fermented tea, despite being treated as such relatively frequently. Rather, it’s a very specific type of fermented tea. To be considered pu’er it must be grown in Yunnan, China and must be from the Camellia sinensis var. assamica. The leaves also must be dried in the sun. There are two types of pu’er: sheng (pronounced “shung”) and shu (pronounced “shoe”--also sometimes spelled ‘shou’ and pronounced “show”). Sheng is a style of pu’er where the leaves are aged naturally over time. Aging here refers to a combination of oxidation and fermentation. This type is less common outside of high end tea circles. Shu is a style of pu’er where the leaves are pile-fermented called wet piling. This was invented in the 1970s in an attempt to mimic the natural aging of sheng pu’er. During wet piling the leaves are piled and covered with damp cloth. Additional moisture is added to the pile and the leaves are left to ferment for around 45 days, being turned occasionally to promote even fermentation.