A category unto itself, like oolong, green or white, Pu-Er could well be called China‚Äôs mystery tea. It has been produced in Yunnan from ancient times and shipped from the market town of Pu-Er until eventually the tea itself acquired this name outside Yunnan. Pu-Er is made tea, either black, green or white, which is then sprayed with an unknown bacterium and allowed to undergo a sort of secondary fermentation. It may be compressed into many shapes or left loose and, unique among teas, it actually improves with age. The best Pu-Er comes from the area called the Six Famous Mountains in Xishuanbanna region. Chinese also call the Pu-Er category Heicha or Dark tea.