A subcategory of dark tea, or heicha, pu-erh is a post-fermented tea made from Yunnan Province. This tea is often aged, which mellows and refines its flavor and character. It is made either as loose leaf or pressed into a myriad of shapes, such as round cakes (bingcha), rectangular bricks, and a birds' nest bowl (tuocha).
There are two main steps in production: The first is making a base tea (mao cha), and the second is post-fermenting and often compressing it. Pu-erh produced before the 1970s was made from sun-dried green tea and naturally aged, a process that is now known as sheng, green or raw. In 1973, a technique for accelerating the process of aging and changing the character of the tea was developed by the Kunming Factory. This process is called wo dui and involves increasing the moisture level as well as the temperature of the tea to speed up the fermentation. These pu-erhs are referred to as shu, brown, or cooked pu-erh.