Black tea is allowed to wither, which precedes a process called oxidation (sometimes incorrectly referred to as fermentation) during which water evaporates out of the leaf and the leaf absorbs more oxygen from the air. Black teas usually undergo full oxidation, and the results are the characteristic dark brown and black leaf, the typically more robust and pronounced flavors of black teas, and when brewed appropriately, a higher caffeine content compared to other teas (50-65% of coffee, depending on the type and brewing technique).