Black Tea is the class of tea that is considered to be fully-oxidized. The processing of Black Tea originated in China, where it is known as Hong Cha, or “Red Tea.” When this fully-oxidized tea came to the west, people saw the black color of the dry leaves and Black Tea got its name.
Black tea is processed to become dark. This means that enzymatic oxidation is encouraged.
With black tea, the leaf is not fired until the leaf has oxidized to a point that the Tea Master making the tea determines is enough. If the tea is not oxidized enough, it will be to green in flavor. Too much oxidation and the tea will taste flat and dusty.
The resulting infusion of a Black Tea is a coppery “red.” This change in color occurs as a result of the way oxidation alters the polyphenols in the tealeaf. Fresh tealeaves are rich in polyphenols (the antioxidants), which have a clear and greenish pigment. When these clear-green polyphenols oxidize, they become Theaflavin, which has a golden-yellow pigment (as with the infusions of oolongs and white teas). In black tea, the Theaflavin has further oxidized and become Thearubigin, which has a reddish pigment.
Due to the hearty tea leaf varietals traditionally selected to make Black Tea, the infusions tend to be higher in caffeine than most other kinds of tea.
Take a look at the Samovar Black Teas. These make a great substitution for coffee by providing energy and hydration.