Tea

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Tea
Green Tea leaves in a Chinese gaiwan.
Type Hot or cold beverage
Country of origin China
Introduced approx. 10th century BC.[1]

Tea is the agricultural product of the leaves, leaf buds, and internodes of the Camellia sinensis plant, prepared and cured by various methods. “Tea” also refers to the aromatic beverage prepared from the cured leaves by combination with hot or boiling water,[2] and is the common name for the Camellia sinensis plant itself. Although tea contains various types of polyphenols, “contrary to widespread belief, tea does not contain tannic acid.” [3]

After water, tea is the most widely-consumed beverage in the world.[4] It has a cooling, slightly bitter, astringent flavour which many enjoy.[5]

There are at least six varieties of tea; white, yellow, green, oolong, black and pu-erh[6] of which the most commonly found on the market are white, green, oolong and black.[7] All tea are made from the same species of plant, though different varieties may be used, and the leaves are processed differently, and, in the case of fine white tea, grown differently. Pu-erh tea, a post-fermented tea, is also often used medicinally.[6]

The term “herbal tea” usually refers to an infusion or tisane of leaves, flowers, fruit, herbs or other plant material that contains no Camellia sinensis.[8] The term “red tea” refers to an infusion made from either black tea (mainly in Chinese, Korean, Japanese and other East Asian languages) or the South African rooibos plant (containing no Camellia sinensis).

Traditional Chinese tea cultivation and technologies

Camellia sinensis is an evergreen plant that grows mainly in tropical and sub-tropical climates. Nevertheless, some varieties can also tolerate marine climates and are cultivated as far north as Pembrokeshire in the British mainland[9] and Washington in the United States.[10]

In addition to a zone 8 climate or warmer, tea plants require at least 50 inches of rainfall a year and prefer acidic soils.[11] Traditional Chinese Tea Cultivation and Studies believes that high-quality tea plants are cultivated at elevations of up to 1,500 metres (4,900 ft): at these heights, the plants grow more slowly and acquire a better flavour.[12]

Only the top 1-2 inches of the mature plant are picked. These buds and leaves are called flushes.[13] A plant will grow a new flush every seven to ten days during the growing season.

A tea plant will grow into a tree if left undisturbed, but cultivated plants are pruned to waist height for ease of plucking.[14]

Two principal varieties are used: the China plant (C. sinensis sinensis), used for most Chinese, Formosan and Japanese teas (but not Pu-erh); and the clonal Assam plant (C. sinensis assamica), used in most Indian and other teas (but not Darjeeling). Within these botanical varieties, there are many strains and modern Indian clonal varieties. Leaf size is the chief criterion for the classification of tea plants:[15] tea is classified into (1) Assam type, characterized by the largest leaves; (2) China type, characterized by the smallest leaves; and (3) Cambod, characterized by leaves of intermediate size.[15]

Processing and classification

A tea's type is determined by the processing which it undergoes. Leaves of Camellia sinensis soon begin to wilt and oxidize, if not dried quickly after picking. The leaves turn progressively darker as their 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 oxidation at a predetermined stage by heating, which deactivates the enzymes responsible. With black tea, this step is executed simultaneously with drying.

Without careful moisture and temperature control during manufacture and packaging, the tea will grow fungi. The fungus causes real fermentation that will contaminate the tea with toxic and sometimes carcinogenic substances, as well as off-flavors, rendering the tea unfit for consumption.

Tea is traditionally classified based on the techniques with which it is produced and processed.[16]

• White tea: Wilted and unoxidized
• Yellow tea: Unwilted and unoxidized, but allowed to yellow
• Green tea: Unwilted and unoxidized
• Oolong: Wilted, bruised, and partially oxidized
• Black tea: Wilted, sometimes 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, higher price, or both, as a more expensive, better-tasting tea may cover the inferior taste of cheaper varieties.

Some teas are not pure varieties, but have been enhanced through additives or special processing. Tea is 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 and flavored variants, such as bergamot (Earl Grey), vanilla, caramel, and many others.

Content

Tea contains catechins, a type of antioxidant. In a freshly-picked tea leaf, catechins can compose up to 30% of the dry weight. Catechins are highest in concentration in white and green teas, while black tea has substantially fewer due to its oxidative preparation.[17][18] Research by the U.S. Department of Agriculture has suggested that levels of antioxidants in green and black tea do not differ greatly, with green tea having an Oxygen Radical Absorbance Capacity (ORAC) of 1253 and black tea an ORAC of 1128 (measured in μmolTE/100g).[19] Tea also contains theanine and the stimulant caffeine at about 3% of its dry weight, translating to between 30 mg and 90 mg per 8 oz (250 ml) cup depending on type, brand[20] and brewing method.[21] Tea also contains small amounts of theobromine and theophylline,[22] as well as fluoride^{[citation needed]}, with certain types of brick tea made from old leaves and stems having the highest levels.[23]

Dry tea has more caffeine by weight than coffee; nevertheless, more dried coffee is used than dry tea in preparing the beverage,[24] which means that a cup of brewed tea contains significantly less caffeine than a cup of coffee of the same size.

Tea has no carbohydrates, fat, or protein.

Origin and history

According to Mondal (2007, p. 519): “Camellia sinensis originated in southeast Asia, specifically around the intersection of latitude 29°N and longitude 98°E, the point of confluence of the lands of northeast India, north Burma, southwest China and Tibet. The plant was introduced to more than 52 countries, from this ‘centre of origin’.”

Based on morphological differences between the Assamese and Chinese varieties, botanists have long asserted a dual botanical origin for tea; however, statistical cluster analysis, the same chromosome number (2n=30), easy hybridization, and various types of intermediate hybrids and spontaneous polyploids all appear to demonstrate a single place of origin for Camellia sinensis — the area including the northern part of Burma, and Yunnan and Sichuan provinces of China.[25] According to this theory, tea plants in southeast Asia may have been the products of the 19th Century and 20th Century hybridizing experiments.^{[citation needed]}