Pu-erh tea

„The leaves are then dry pan-fried using a large wok in a process called "kill green" (殺青; pinyin: shā qīng), which arrests most enzyme activity in the leaf and prevents full oxidation. After pan-frying, the leaves are rolled, rubbed, and shaped into strands through several steps to lightly bruise the tea and then left to dry in the sun.“

„Sourness in Raw Puer is due mostly to inadequate airing after the rolling process or, after pressing tea into cakes, they have been immediately exposed to the sun. The tea soup will likely be turbid.“