Black tea is made from the leaves of a bush called Camellia sinensis. It has caffeine as well as other stimulants and antioxidants. Lots of people in the U.S. drink it either hot or cold. It should always be steeped in hot water before it is cooled. A process called oxidation turns the leaves from green to a dark brownish-black colour. Oxidation means the leaves are exposed to moist, oxygen-rich air.