Tea is an aromatic beverage prepared by pouring boiling hot water over cured leaves of the Camellia Sinensis, an evergreen plant that grows mainly in tropical and sub-tropical climates. After water, tea is the most widely consumed beverage in the world with a cooling, bitter and astringent flavour. Tea plants are native to East and South Asia and probably originated around the point of confluence of the lands of North East India, North Burma and South West China. Some varieties can also tolerate marine climates and are cultivated as far north as Pembrokeshire in the British mainland.
A tea plant will grow into a tree of up to 16 metres (52 ft.) if left undisturbed, but cultivated plants are pruned to waist height with only the top 1 to 2 inches of the mature plant being picked. These buds and leaves are called flushes. A plant will grow a new flush every seven to fifteen days during the growing season, and leaves that are slow in development, like those grown at altitude, always produce better flavoured teas.
The first recorded drinking of tea is in China, dating back to the 10th century BC, already a common drink during the Qin Dynasty (3rd century BC) becoming widely popular during the Tang Dynasty, when it spread to Korea and Japan. Trade of tea by the Chinese to Western nations in the 19th century spread tea and the tea plant to numerous locations around the world. Catherine of Braganza, wife of Charles II, took the tea habit to Great Britain around 1660.
There are at least six different types of tea: white, yellow, green, oolong, black, and post-fermented teas of which the most commonly found on the market are White, Green, Oolong and Black. After picking, the leaves soon begin to wilt and oxidize unless they are immediately dried. The leaves turn progressively darker as the chlorophyll breaks down and tannins are released. This enzyme driven oxidation process is known as fermentation. In tea processing, the darkening is stopped at a predetermined stage by heating, which deactivates the enzymes responsible. In the production of black teas, the halting of oxidization by heating is carried out simultaneously with drying.
Tea is traditionally classified based on the techniques with which it is produced and processed : 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) and Post-fermented tea (Green tea that has been allowed to ferment/compost).
Most teas sold in the West are blended with the aim of obtaining a better taste and higher price. Tea is highly receptive to the inclusion of various aromas which allows for the design of an almost endless range of scented and flavoured variants, such as Bergamot (Earl Grey), Vanilla, and many others.
Tea leaves contain more than 700 chemicals, among which are a number of compounds closely related to human health and longevity, some with germicidal properties, antioxidants that have anti carcinogenic, mutagenic and tumoric properties and others that can reduce stress by inducing a calm but alert, focused, and relatively productive mental state. Tea also plays an important role in improving beneficial intestinal microflora, as well as providing immunity against intestinal disorders. It is associated with a lower risk of diseases that cause functional disability, such as “stroke, cognitive impairment, and osteoporosis” in the elderly, with drinkers enjoying significantly less cognitive decline than non-tea drinkers.
Protective effects from tea consumption are observed less frequently in populations where the intake of black tea predominates.