After harvesting, the tea leaves are subjected to light steaming or gentle heat to prevent certain natural changes from taking place. In particular, this processing inhibits the auto-oxidation caused by natural enzymes present in the freshly picked tea leaves. If oxidation is allowed to proceed unchecked, it would eventually convert the tea to oolong and then black tea. The gentle processing, however, prevents this oxidation, thus preserving important natural antioxidants in the leaves. The result is green tea.
Black tea has a stronger flavor and darker color than green tea.
The tea leaves are processed more than green tea, including auto-oxidation, which turns the tea a dark brown or reddish color. Black tea is the most popular tea world wide, constituting nearly 80 percent of all tea produced and drunk. Despite its name, however, oolong tea is the happy medium between green and black tea.