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世紀(jì)時(shí)，茶是乾隆皇帝最喜歡的飲品。現(xiàn)在，越來(lái)越多的人把茶作為他們的最?lèi)?ài)。除了能賣(mài)茶葉外，茶商還把茶提煉出來(lái)添加到口香糖，軟飲料和潤(rùn)膚露中，在亞洲，甚至添加到kit貓棒棒糖中。

    綠茶是茶樹(shù)的干葉子制成的，而茶樹(shù)是亞洲本地的一種常青樹(shù)。這種樹(shù)豐收時(shí)，可以用不同的方式制作成綠茶或黑茶。

    豐收后，把葉子蒸片刻，綠茶就制好了。蒸餾的作用是破壞葉子中的酶而不使其中的化學(xué)成分被氧化得太多。蒸餾后就把葉子壓碎。

    如果是制作黑茶，先發(fā)酵幾天，然后加熱，這樣做是為了使葉子變黑，還有在其中產(chǎn)生多種化學(xué)變化。  

    這些處理方式的不同可能具有很重要的藥用價(jià)值。各種類(lèi)型的茶都富含有某種被稱為類(lèi)黃酮的抗氧化物質(zhì)，黃體酮的起防止自由基破壞細(xì)胞的作用。由于沒(méi)有發(fā)酵，綠茶富含類(lèi)黃酮，這種物質(zhì)就是俗稱的兒茶酚。兒茶酚，兒茶素或是EGCG的藥效都很強(qiáng)，而綠茶中它們的含量是黑茶的三到四倍。