Green tea is the unfermented form of tea. It starts with the same type of plant as black or oolong tea but the processing is very different. The leaves are steamed in order to inactivate the enzymes at the first stage of processing. (Black tea, by contrast is dried over dry heat which increases enzyme and therefore caffeine.) After this it is rolled, then fired at a high temperature to fix the flavor of the tea.

Green tea has less caffeine than black tea; approximately 20 mg per cup as opposed to black tea which has approximately 40mg. (Coffee, by comparison, has 80 - 100.)