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.

    在18世纪时，茶是乾隆皇帝最喜欢的饮品。现在，越来越多的人把茶作为他们的最爱。除了能卖茶叶外，茶商还把茶提炼出来添加到口香糖，软饮料和润肤露中，在亚洲，甚至添加到kit猫棒棒糖中。

    绿茶是茶树的干叶子制成的，而茶树是亚洲本地的一种常青树。这种树丰收时，可以用不同的方式制作成绿茶或黑茶。

    丰收后，把叶子蒸片刻，绿茶就制好了。蒸馏的作用是破坏叶子中的酶而不使其中的化学成分被氧化得太多。蒸馏后就把叶子压碎。

    如果是制作黑茶，先发酵几天，然后加热，这样做是为了使叶子变黑，还有在其中产生多种化学变化。  

    这些处理方式的不同可能具有很重要的药用价值。各种类型的茶都富含有某种被称为类黄酮的抗氧化物质，黄体酮的起防止自由基破坏细胞的作用。由于没有发酵，绿茶富含类黄酮，这种物质就是俗称的儿茶酚。儿茶酚，儿茶素或是EGCG的药效都很强，而绿茶中它们的含量是黑茶的三到四倍。