Black, green, and white teas are all made from leaves of the same species of plant, but their differences arise from the level of oxidation that they have undergone during processing. Once tea leaves are picked, they begin to wither. Exposure to oxygen triggers a series of chemical reactions that cause the leaves to turn brown, but it also triggers the production of chemical compounds that change its flavour.
White tea is produced from the youngest tea leaves, which are allowed to dry naturally, resulting in a low level of oxidation. At the other end of the spectrum, black tea undergoes more extensive processing. First leaves are left to wilt in sunlight. Then they are crushed, creating cell damage that helps oxidation to occur, and exposed to warm, humid conditions. Finally, heating in an oven terminates the oxidation process. A higher degree of oxidation increases the production of compounds called xanthines, including caffeine, and gives black tea its dark colour.