All green teas are not the same. Indian and Chinese green teas are usually oven-dried rather than steamed. Simple drying can cause oxidation of important vitamins, minerals, and flavor components, which can alter the taste and nutritional content of delicate green teas.
Recent chemical analysis has revealed that because Japanese green teas are steamed immediately after they are picked, most of their oxidative enzymes are destroyed. Consequently, they retain their green color, natural vitamins, and high concentration of polyphenols. Moreover, the amino acid content, which determines the depth of flavor in green teas, is much higher in Japanese teas.