Tea

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 . (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, and polyphenolic antioxidant catechins. It has almost no carbohydrates, fat, or protein. It has a cooling, slightly bitter, and astringent flavor.

Cultivation

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. 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. Only the top 1-2 inches of the mature plant are picked. These buds and leaves are called flushes, and a plant will grow a new flush every seven to ten days during the growing season.

Tea is commercially cultivated as far north as Tregothnan in Cornwall on the UK mainland.

Tea plants will grow into a tree if left undisturbed, but cultivated plants are pruned to waist height for ease of plucking.

Two principal varieties are used, the small-leaved China plant (C. sinensis sinensis) and the large-leaved Assam plant (C. sinensis assamica).

Processing and classification

Tea plant (Camellia Sinensis) from Köhler's Medicinal Plants.

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:

• Green tea: Un-wilted and unoxidized
• Yellow tea: Un-wilted and unoxidized but allowed to yellow
• White tea: Wilted and unoxidized
• Oolong: Wilted, bruised, and partially oxidized
• Black tea/Red tea: Wilted, crushed, and fully oxidized
• Post-fermented tea: Green Tea that has been allowed to ferment/compost

Blending and additives

Almost all teas in bags and most other teas sold in the West are blends. Blending may occur in the tea-planting area (as in the case of Assam), or teas from many areas may be blended. The aim is to obtain better taste, better price or both, as more expensive, better-tasting tea may cover the inferior taste of cheaper varieties. Blending may also achieve more consistent taste of the blend, regardless of the variation of taste among pure teas.

Various teas, as sold, are not pure varieties but have been enhanced through additives or special processing. Tea is indeed highly receptive to inclusion of various aromas; this may cause problems in processing, transportation and storage, but also allows for the design of an almost endless range of scented variants, such as vanilla-flavored, caramel-flavored and many others.

Content

Tea contains catechins, a type of antioxidant. In a fresh tea leaf, catechins can be up to 30% of the dry weight. Catechins are highest in concentration in white and green teas, while black tea has substantially less due to its oxidative preparation. Tea contains theanine, and the stimulant caffeine at about 3% of its dry weight, translating to between 30mg and 90mg per 8oz (or 0.25 L) cup depending on type and brand and brewing method. Tea also contains small amounts of theobromine and theophylline. Tea also contains fluoride, with certain types of brick tea made from old leaves and stems having the highest levels.