Difference between revisions of "Tea"
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Revision as of 13:54, 23 July 2012
| Infobox on Tea | |
|---|---|
| Example of Tea |  |
| Facts | |
| Origin | This table shows only a selection of the most important countries of origin and should not be thought of as exhaustive.
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| Stowage factor (in m3/t) |
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| Humidity / moisture | Water content 4-6% (black tea), RH 60% |
| Oil content | 1% essential oils |
| Ventilation | If the product is at "shipping dryness", i.e. if there is no risk of degradation by mold etc. due to water content, ventilation is not required. If this is not the case, then 10 air changes/hour should be implemented |
| Risk factors | Tea is extremely sensitive to foreign odors, contamination, moist, mechanical stresses and insect infestation. |
Tea
Description
Camellia sinensis is an evergreen plant that grows mainly in tropical and sub-tropical climates.
Tea plants are propagated from seed or by cutting; it takes approximately 4 to 12 years for a tea plant to bear seed, and about 3 years before a new plant is ready for harvesting. In addition to warm(er) zone, tea plants require at least 127 cm. (50 inches) of rainfall a year and prefer acidic soils. Many high-quality tea plants are cultivated at elevations of up to 1.500 metres: at these heights, the plants grow more slowly and acquire a better flavour.
Only the top 1-2 inches of the mature plant are 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 always produce better flavored teas.
A tea plant will grow into a tree of up to 16 metres if left undisturbed, but cultivated plants are pruned to waist height for ease of plucking.
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 tea 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, with three primary classifications being: Assam type, characterized by the largest leaves; China type, characterized by the smallest leaves; and Cambod, characterized by leaves of intermediate size. The smaller the leaf, the more expensive the tea.
Teas can generally be divided into categories based on how they are processed. 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. Some varieties, such as traditional oolong tea and Pu-erh tea, a post-fermented tea, can be used medicinally.
After picking, the leaves of Camellia sinensis soon begin to wilt and oxidize, unless they are immediately dried. The leaves turn progressively darker as their chlorophyll breaks down and tannins are released. This enzymatic oxidation process, known as fermentation in the tea industry, is caused by the plant's intracellular enzymes and causes the tea to darken. 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.
Without careful moisture and temperature control during manufacture and packaging, the tea may become unfit for consumption, due to the growth of undesired molds and bacteria. At minimum it may alter the taste and make it undesirable.
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 |
| Post fermented tea | Green tea that has been allowed to ferment/compost |
Although single estate teas are available, 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 of blending 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.
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. Tea also contains L-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 and brewing method.
Tea also contains small amounts of theobromine and theophylline. Due to modern day environmental pollution fluoride and aluminium have also been found to occur in tea, with certain types of brick tea made from old leaves and stems having the highest levels. This occurs due to the tea plant's high sensitivity to and absorption of environmental pollutants.
Although tea contains various types of polyphenols and tannin, tea does not contain tannic acid. Tannic acid is not an appropriate standard for any type of tannin analysis because of its poorly defined composition.
Applications
Tea leaves are used to make an infused beverage which is classed as a semiluxury item.
Shipment/storage
A distinction is drawn between the China tea plant (e.g. from China, Japan and Taiwan) and the Assam tea plant (e.g.. from India, Sri Lanka, Indonesia and Vietnam), each variety yielding both leafy and broken grades of tea. Teas are also classified and graded depending upon the size of the tea leaves. The youngest, small top leaves (= pekoe tips) provide the most valuable teas, while the older, large bottom leaves provide less valuable grades.
Grades of tea are classified by:
- Country of origin
- Leaf size/shape
| Leafy/broken | Abbreviation | Designation | Leaf shape | |
| Leafy grades | F.O.P. | Flowery orange pekoe | Thin, wiry, often with a light covering of silky hairs | |
| O.P. | Orange Pekoe | Slightly twisted, often with white to golden yellow tips | ||
| P. | Pekoe | Somewhat coarser | ||
| S. | Souchang | Coarse | ||
| Broken grades | F.B.O.P. | Flowery broken orange pokoe | ||
| B.O.P. | Broken Pekoe | |||
| B.T. | Broken tea | |||
| Low grades | F | Fanings | The leaf particles and fragments obtained during processing | |
| D. | Dust | Finely divided tea dust | ||
| B. | Bohea |