Pu-erh is the only major tea category that is meant to age. Most teas are at their best within a year of being picked. Pu-erh is often better at fifteen, twenty, fifty years old.
It comes from Yunnan province in southwestern China, made from a variety of the tea plant with larger leaves than most — often from trees rather than bushes. There are two kinds: raw (sheng), which slowly transforms in storage over decades, and ripe (shou), which is pushed through an accelerated fermentation in a matter of weeks. Both are usually pressed into cakes, bricks, or other shaped forms.