Black tea is fully fermented, which blackens the leaves and causes the formation of caffeine and tannins. It generally possesses the most robust flavor and highest level of caffeine.

Black teas originated in China, where they are known as red tea, but now come from many growing regions throughout the world. The traditional method of processing black teas comprises four steps: withering, rolling, oxidizing and drying. First the leaves are spread out on racks of bamboo or woven straw to be wilted until soft enough to be rolled without tearing the leaf. Next, the withered leaf is rolled to release the chemicals in the leaf that will contribute to the tea's final color and flavor. Rolling will also determine the shape of the leaves and this will also impact the tea's flavor and pungency. The rolled leaves are spread out in cool and humid rooms and exposed to oxygen for several hours, which causes chemical changes in the leaves and turns them from green to coppery red. Finally, the completely oxidized leaves are fired (or dried) to stop oxidation. In China, the leaves are traditionally fired in hot woks. In other areas, the leaves may be baked in hot ovens