Pu-erh tea, also spelled as Pu'er tea is a variety of post-fermented tea produced in Yunnan province, China. Post-fermentation is a tea production style in which the tea leaves undergo a microbial fermentation process after they are dried and rolled. This is a Chinese specialty and is sometimes referred to as dark tea. There are a few different provinces, each with a few regions, producing dark teas of different varieties. Those produced in Yunnan are generally named Pu'er, referring to the name of Pu'er county which used to be a trading post for dark tea during imperial China.