Tea
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Tea is a beverage made by steeping processed leaves, buds, or twigs of the tea bush, Camellia sinensis, in hot water for a few minutes. The processing can include oxidation, heating, drying, and the addition of other herbs, flowers, spices, and fruits. The four basic types of true tea are (in order from most to least processed): black tea, oolong tea, green tea, and white tea. The term “herbal tea” usually refers to infusions of fruit or of herbs (such as rosehip, chamomile, or jiaogulan) that contain no Camellia sinensis .[2] (Alternative terms for herbal tea that avoid the word “tea” are tisane and herbal infusion.) This article is concerned exclusively with preparations and uses of the tea plant C. sinensis.
Tea is a natural source of the amino acid theanine, methylxanthines such as caffeine and theobromine,[3] and polyphenolic antioxidant catechins.[4] It has almost no carbohydrates, fat, or protein. It has a cooling, slightly bitter, and astringent flavor.[4]
Camellia sinensis is an evergreen plant and grows in tropical to sub-tropical climates. In addition to tropical climates (at least 50 inches of rainfall a year), it also prefers acidic soils[citation needed]. Many high quality tea plants grow at elevations up to 1500 meters (5,000 ft), as the plants grow more slowly and acquire a better flavor[citation needed]. Only the top 1-2 inches of the mature plant are picked. These buds and leaves are called flushes,[5] and a plant will grow a new flush every seven to ten days during the growing season.
Tea plants will grow into a tree if left undisturbed, but cultivated plants are pruned to waist height for ease of plucking.[6]
Two principal varieties are used, the small-leaved China plant (C. sinensis sinensis) and the large-leaved Assam plant (C. sinensis assamica).
These types of tea are distinguished by the processing they undergo. Leaves of Camellia sinensis soon begin to wilt and oxidize if not dried quickly after picking. The leaves turn progressively darker because chlorophyll breaks down and tannins are released. This process, enzymatic oxidation, is called fermentation in the tea industry although it is not a true fermentation: it is not caused by micro-organisms, and is not an anaerobic process. The next step in processing is to stop the oxidation process at a predetermined stage by heating, which deactivates the enzymes responsible. With black tea this is done simultaneously with drying. Without careful moisture and temperature control during its manufacture and thereafter, fungi will grow on tea. This form of fungus causes real fermentation that will contaminate the tea with toxic and sometimes carcinogenic substances and off-flavours, rendering the tea unfit for consumption.
Tea is traditionally classified based on producing technique :[7]
