In producing black tea, harvested leaves are spread on withering racks to dry. The leaves become soft and pliable and are then roller-crushed to break the cell walls, releasing the enzymes and tannins that give tea its unique flavor. After rolling, the tea leaves are spread in a fermentation room, where they oxidize, turning a copper color. Finally the leaves are dried in hot air, a process that stops the fermentation and turns the leaves black. The tea is then sieved to produce leaves of a uniform size and to facilitate blending and packing.
Tea grades refer to the size of the tea leaf.
Fannings fill the world's tea bags. The tea plant grown in Taiwan and south China appears to be most suitable for preparing oolong tea. The process begins in the same manner as that for black tea. The aroma, however, develops more quickly, and when the leaf is fired or dried, a coppery color forms around the edge of the leaf while the center remains green. The flavor is fruity and pungent.