Pu-erh tea

„Nèi fēi (内飞 or 內飛): A small ticket originally stuck on the tea cake but now usually embedded into the cake during pressing. It is usually used as proof, or a possible sign, to the authenticity of the tea. Some higher end pu'er cakes have more than one nèi fēi embedded in the cake. The ticket usually indicates the tea factory and brand.“

„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.“