Tea was 18th century Chinese Emperor Chien Lung's favorite drink. Now more and more people also share that preference. In addition to selling green tea leaves, tea merchants have distilled the brew's essence and added it to gum, soft drinks and skin creams - even, in Asia, to Kit Kat candy bars.

Green tea is made from the dried leaves of Camellia sinensis, an evergreen shrub native to Asia. The plant is harvested and treated in different ways to produce green tea or black tea.

Green tea is made by steaming the leaves shortly after harvest, destroying enzymes so that chemicals aren't oxidized very much. Then the leaves will be crushed.

Leaves used for black tea ferment for days before they're heated, causing the leaves to blacken and many chemical changes to happen within them.

Those processing differences may be medicinally important. Both types of tea are abundant in certain antioxidant chemicals called flavonoids, which obstruct the action of cell-damaging free radicals. Green tea, because it doesn't ferment, has much higher levels of a group of flavonoids called catechins. A potent catechin, epigallocatechin gallate, or EGCG, is three to four times more abundant in green tea than black.