Although it contains caffeine, the tannins in tea interact with the caffeine so as not to have the strength of caffeine found in coffee. The variations are scented or smoked. It is interesting to note that both green and black teas are derived from the same plant. The difference lies in the treatment of the leaf after it is picked. Leaves destined to make black tea are fermented whereas those for green tea are dried in the sun or in drying rooms.
Oolong is fermented to less than half of the extent of black.
To make black tea, the leaves are spread on a screen and are dried either by the sun or by a gentle current of hot air. Next, they are rolled to expose and oxidize the juice, then left to wilt on cool tables that may be made of metal, stone, glass, or tile, then fried over charcoal. For green tea, the leaves may or may not be withered first. They are de-enzymized by pan frying. Sometimes, they are steamed to softness and rolled on mats.