Green teas have been popular in Asia for well over a thousand years. Consequently, they are wrapped in tradition and produced in forms that are unlike any other types of tea. Many green teas are simply dried before they oxidize and sold as whole leaf teas, much as black teas are. Just as commonly in Japan, though, green teas are processed into a powder that is mixed with hot water rather than steeped. In other cases, tea is made from the stems of tea leaves, usually coupled with tea powder. Regardless of their production, green teas are uniquely smooth and relaxing, with a very low caffiene content. They are also among the healthiest teas available, according to numerous medical studies.