Tea is the second most widely consumed beverage in the world after water. Regular intake of tea is associated with improved antioxidant status in vivo, which may contribute to lowering the risk of coronary heart disease, stroke, and certain types of cancer. There are three major categories of tea: the nonfermented green tea, the partially fermented oolong tea, and the fully fermented black tea. (actually it is oxidation)Besides these three major teas, other teas, such as white tea and Pu-erh tea(post-femented), have also been introduced to the Western marketplace in recent years. In China, it into six types:white tea,green tea,yellow tea,oolong tea,black tea and dark tea,which are distinguished by the processing method.
Camellia sinensis (L.) Kuntze is a perennial leafy crop. All varieties of tea are producedfrom the tea plants. Tea plants prefer a warm and humid climate with plentyof rainfall and also like diffused light and weak acidic and well-drained soil. Thewell-grown tea plants provide high-quality tea shoots, which vary with tea cultivarsand the environmental conditions, such as the type of soil and altitude and climate ofthe tea plant growing area. A Chinese idiom says, “A higher mountain yields higherquality tea,” which indicates that the mountain conditions are optimum to tea plantgrowth, especially the growth of high-quality flush.
Moreover, tea quality is also determined by the processing techniques employed. For instance, the same freshtea leaves can be processed to black tea, oolong tea, and green tea by fermentation,semifermentation, and nonfermentation, respectively. Those basic three types of teahave different quality characteristics, including color, aroma, taste, and appearance.The fresh tea leaves are usually used for tea manufacturing and are harvestedby hand plucking or mechanical plucking. Compared to mechanical plucking, handplucking is more labor intensive and time consuming and less efficient, but withhigher uniformity. The well-known high-quality green teas are mostly producedfrom hand-plucking fresh tea leaves in China. Fresh tea leaves could be harvestedduring different seasons in a year, which changes with the climate of tea growingarea. In China, the leaves are plucked in spring, summer, and autumn; in winter thetea bush is dormant. After being plucked, the fresh tea leaves are sent immediatelyto tea factories for manufacturing.
According to the different ways of processing, especially
(1)the extent of fermentation,tea is usually divided into three basic types: green tea (nonfermented), oolongtea (semifermented) and black tea (fully fermented).
Alternatively, with the combinationof the (2)ways of processing and the characteristic quality of manufactured tea, teais classified into six types: green tea, yellow tea, dark tea (containing brick tea andpu-erh tea), white tea, oolong tea, and black tea
.The so-called fermentation in tea processing is not the anaerobic breakdown of an energy-rich compound (asa carbohydrate to carbon dioxide and alcohol or to an organic acid), but in essenceis mainly the oxidative polymerization and condensation of catechins catalyzed byendogenous polyphenol oxidase and peroxidase.
The oxidation products such astheaflavins茶黄素 and thearubigins茶红素 contribute to tea color and the taste of black tea.Unlike either black tea or green tea, oolong tea has an excellent characteristicwith the combination of the freshness of green tea and the fragrance of black tea. Itis produced by a special process called green leaf shaking (yaoqing)摇青 and green leafcooling (liangqing). 晾青In this process, the moderately withering green tea leaves arebruised at the edges by hand or mechanical shaking and vibrating. The leaf appearanceof oolong tea is featured with the reddish edges and green centers.绿叶红镶边 Oolong tea isproduced in China, particularly in Fujian, Guangdong, and Taiwan, and is currentlypopular in China and Southeastern Asia. It has a good function in helping bodybuilding and dieting.