Tea Longjing green tea being infused in a gaiwan Type

Camellia sinensis is an evergreen plant that grows mainly in tropical and subtropical climates.^[54] Some varieties can also tolerate marine climates and are cultivated as far north as Cornwall in England,^[55] Perthshire in Scotland,^[56] Washington in the United States,^[57] and Vancouver Island in Canada.^[58] In the Southern Hemisphere, tea is grown as far south as Hobart in Tasmania^[59][60] and Waikato in New Zealand.^[61]

Tea plants are propagated from seed and cuttings; about 4 to 12 years are needed for a plant to bear seed and about three years before a new plant is ready for harvesting.^[54] In addition to a zone 8 climate or warmer, tea plants require at least 127 cm (50 in) of rainfall per year and prefer acidic soils.^[62] Many high-quality tea plants are cultivated at elevations of up to 1,500 m (4,900 ft) above sea level. Though at these heights the plants grow more slowly, they acquire a better flavour.^[63]

Women tea pickers in Kenya

Two principal varieties are used: Camellia sinensis var. sinensis, which is used for most Chinese, Formosan and Japanese teas, and C. sinensis var. assamica, used in Pu-erh and most Indian teas (but not Darjeeling). Within these botanical varieties, many strains and modern clonal varieties are known. Leaf size is the chief criterion for the classification of tea plants, with three primary classifications being:^[64] Assam type, characterised by the largest leaves; China type, characterised by the smallest leaves; and Cambodian type, characterised by leaves of intermediate size. The Cambodian-type tea (C. assamica subsp. lasiocaly) was originally considered a type of Assam tea. However, later genetic work showed that it is a hybrid between Chinese small-leaf tea and Assam-type tea.^[65] Darjeeling tea also appears to be a hybrid between Chinese small-leaf tea and Assam-type large-leaf tea.^[66]

Tea plantation near Sa Pa, Vietnam

A tea plant will grow into a tree of up to 16 m (52 ft) if left undisturbed,^[54] but cultivated plants are generally pruned to waist height for ease of plucking. Also, the short plants bear more new shoots which provide new and tender leaves and increase the quality of the tea.^[67] Only the top 2.5–5 centimetres (1–2 in) of the mature plant are picked. These buds and leaves are called 'flushes'.^[68] A plant will grow a new flush every 7 to 15 days during the growing season. Leaves that are slow in development tend to produce better-flavoured teas.^[54] Several teas are available from specified flushes; for example, Darjeeling tea is available as first flush (at a premium price), second flush, monsoon and autumn. Assam second flush or "tippy" tea is considered superior to first flush, because of the gold tips that appear on the leaves.

Pests that can afflict tea plants include mosquito bugs, genus Helopeltis, which are true bugs and not to be confused with dipterous insects of family Culicidae ('mosquitos'). Mosquito bugs can damage leaves both by sucking plant materials, and by the laying of eggs (oviposition) within the plant. Spraying with synthetic insecticides may be deemed appropriate.^[69] Other pests are Lepidopteran leaf feeders and various tea diseases.

Chemical composition[edit]

See also: Phenolic content in tea and Health effects of tea

Physically speaking, tea has properties of both a solution and a suspension. It is a solution of all the water-soluble compounds that have been extracted from the tea leaves, such as the polyphenols and amino acids, but is a suspension when all of the insoluble components are considered, such as the cellulose in the tea leaves.^[70] Tea infusions are among most consumed beverages globally.^[71]

Caffeine constitutes about 3% of tea's dry weight, translating to between 30 and 90 milligrams per 250-millilitre (8+¹⁄₂ US fl oz) cup depending on the type, brand,^[72] and brewing method.^[73] A study found that the caffeine content of one gram of black tea ranged from 22 to 28 mg, while the caffeine content of one gram of green tea ranged from 11 to 20 mg, reflecting a significant difference.^[74] Tea also contains small amounts of theobromine and theophylline, which are stimulants, and xanthines similar to caffeine.^[75]

Fresh tea leaves in various stages of growth

Black and green teas contain no essential nutrients in significant amounts, with the exception of the dietary mineral manganese, at 0.5 mg per cup or 26% of the Reference Daily Intake (RDI).^[76] Fluoride is sometimes present in tea; certain types of "brick tea", made from old leaves and stems, have the highest levels, enough to pose a health risk if much tea is drunk, which has been attributed to high levels of fluoride in soils, acidic soils, and long brewing.^[77]

The astringency in tea can be attributed to the presence of polyphenols. These are the most abundant compounds in tea leaves, making up 30–40% of their composition.^[78] Polyphenols include flavonoids, epigallocatechin gallate (EGCG), and other catechins.^[79][80] Although there has been preliminary clinical research on whether green or black teas may protect against various human diseases, there is no evidence that tea polyphenols have any effect on health or lowering disease risk.^[81][82]

Processing and classification[edit]