Thea


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Thea

 

(tea), a genus of tropical perennial evergreen plants of the family Theaceae; some botanists place the plants in the genus Camellia. There are two species: T. sinensis and T. assamica. The former, which is divided into Chinese and Japanese varieties, is a shrub reaching 3 m in height; it grows in mountainous regions of Southeast Asia. T. assamica, a tree measuring as much as 10–15 m in height, occurs in the forests of Assam, India. Varieties of T. assamica include Assam, Lushai, Naga Hills, Manipuri, and Burma. T. assamica also includes a natural hybrid of T. sinensis and T. assamica, which is known as Ceylon tea. Both species are widely cultivated.

In the USSR local hybrids of the Chinese variety of T. sinensis are most commonly cultivated; T. assamica and the Japanese variety of T. sinensis are added to the principal plantings. Sometimes a third species, T. maliflora from China, is designated.

T. sinensis is densely branched. The oval or elongate-oval leaves are slightly narrowed at the base; they measure 60–70 mm long and 35–40 mm across. The leaves are dark green above and light green beneath. The primary root extends 2–3 m into the soil; the lateral roots lie in the surface layer of soil. The fragrant white or pink flowers are solitary or in groups of two, three, or four in the leaf axils. The fruit is a capsule with one to five dark brown hard-shelled seeds, which are rich in oil; the capsule dehisces upon maturation. One thousand seeds weigh about 1 kg.

The tea plant is thermophile and hygrophilous. It grows and develops well when the sum of average daily temperatures during the vegetative period is no less than 4,000°C. The plant tolerates brief frosts to – 12°C without a snow cover (some varieties withstand temperatures as low as –14°C). In tropical areas the tea plant yields a harvest throughout the year. In the humid subtropics of the USSR vegetation begins in March or April, when the average daily temperature is higher than 10°C. Intensive shoot formation begins at temperatures no lower than 17°C. A harvest of 4,000 kg of leaf per hectare (ha) depletes 150 kg of N, 23.9 kg of P2O5, and 47.8 kg of K2O from the soil. The best soils for tea cultivation are red and yellow soils that are highly permeable by air and water.

Tea is propagated by seeds or by vegetative methods. One- or two-year-old plants raised from seed in nurseries are set out in the fields, or the fields are planted with seeds or cultivated with semilignified grafts and cuttings. The tea plant flowers in the fourth or fifth year and forms fruits annually. In the USSR the flowering season is from September until the onset of frost. Cross-pollination is by bees, flies, or other insects. The plant is fully formed by the seventh or eighth year. Productive shoots form annually from the growth buds in the leaf axils; it is the apices of these shoots—two or three leaves and the bud—that are harvested for the manufacture of tea. (The leaves harvested for tea are called the flush.) The growing period of productive shoots is 35 to 65 days. Under favorable conditions the shoots grow continuously. In the USSR two periods of intensive growth are observed: the spring period in May and the summer period in July and August. A tea plant lives 100 or more years; it is most productive from the tenth to 70th year.

Tea was first cultivated in China in the fourth century A.D.; the use of tea as a beverage is mentioned in manuscripts of 2700 B.C. The cultivation of tea in Japan and Korea dates to the ninth century. Tea cultivation was introduced to Indonesia in 1824, to India in 1834, and to Ceylon in 1842. The world area of tea plantations was 1.298 million ha in 1961–65 and 1.502 million ha in 1974. In 1974 the principal tea producers abroad were India (360,000 ha), China (336,400 ha), Sri Lanka (240,000 ha), Indonesia (102,400 ha), and Japan (63,000 ha). The plant is also grown in Africa (Kenya and other countries) and South America (Argentina).

In Russia tea was first used as a beverage in 1638, when the Mongol Altyn Khan sent Tsar Mikhail Fedorovich a gift of four poods of tea leaves. In 1679 an agreement was concluded with China for regular deliveries of tea to Russia. In the 18th century tea imports increased, and the popularity of the beverage rose. The appearance of Russian samovars dates from this period. The botanist N. A. Gartvis planted the first tea shrub in Russia in 1814 in the Nikita Botanical Garden, but the natural conditions of the Crimea proved unfavorable for growing tea. In 1847 tea cuttings acclimatized well at the Ozurgety Experiment Station (now the city of Makharadze) in Georgia. At the All-Russian Exposition of 1864, M. Eristavi demonstrated Georgian tea prepared from leaves gathered from a small tract in Gora-Berezhauli in Ozurgety District. In 1885, A. A. Solovtsev founded Russia’s first commercial tea plantation in Chakva (Adzharia). The plant has been cultivated in what is now Krasnodar Krai since 1901 and in Azerbaijan since 1912. In 1913 the area of tea plantings in Russia was less than 900 ha, the gross yield of leaf was 550 tons, and the average yield was 6.1 quintals per ha.

After the October Revolution of 1917 tea cultivation developed rapidly. New plantations were established in Georgia, Azerbaijan, and Krasnodar Krai. In 1965 tea plantations in the USSR occupied 71,000 ha, the gross harvest of leaf from commercial plantations was 197,000 tons, and the average yield was 33.8 quintals per ha; in 1976 the corresponding figures were 76,800 ha, 375,000 tons, and about 50 quintals per ha.

Soviet plant breeders have developed—for the first time in the history of tea cultivation—local varieties of tea. The varieties Gruzinskii 1, Gruzinskii 2, Zimostoikii, and Kolkhida (a clonal variety) were developed by K. E. Bakhtadze at the All-Union Research Institute of Tea and Subtropical Crops. These local varieties yield 25 to 60 percent more than nonvarietal plantings. The establishment of new plantations and the replacement of old ones have been achieved with vegetatively propagated homogeneous varietal plant material. In 1976 nine varieties of tea were regionalized in the USSR.

Forest or shrub areas are used for tea plantations. Forest belts are planted around the plantation, overly moist lands are drained, and terraces are constructed on steep slopes. Autumn plowing is done to a depth of 45 cm. Inorganic fertilizers (150–200 kg/ha P2O5 and 100–140 kg/ha K20) are applied to exhausted or eroded soils, and then the fields are planted with legumes and cereal grasses. The field is plowed in the second or third year to a depth of 20–25 cm. On fertile lands no sodding is provided; manure (40–50 tons/ha) and inorganic fertilizers (up to 300 kg/ha P2O5) are applied before plowing. Green manuring is effective: lupine, serradella, and other plants are set out in summer and plowed under in early spring.

In the USSR espalier planting in dense rows is the most common method of planting tea. The distance between espaliers is 1.25 to 2.05 m. The young plants must be kept shaded, and the soil between rows must be loosened several times throughout the summer. Before the annual autumn shallow plowing, manure (40–50 tons/ha), phosphorus (100–150 kg/ha P2O5), and potassium (150–250 kg/ha K2O) are applied. In the summer nitrogenous fertilizers (50 to 400 kg/ha N—depending on the age of the planting) are administered. Pruning and espalier formation by means of special pruning apparatus ensure maximum shoot formation and the formation of a broad semioval crown 60–80 cm in width and 50–70 cm tall. Withered and diseased branches must be removed regularly, and the fields must be irrigated. In the USSR the flushes are gathered manually or with tea-harvesting machines from late April or early May to October. After gathering, the tea leaf is cleaned with a special machine.

The most harmful diseases of the tea plant are bacterial wart, brown and gray leaf spot, and cercoseptoriosis. Pests include the cushion scale (Pulvinaria floccifera), armored scales (Diaspididae), the tea aphid (Aphis theae), and the tea moth (Parametriotes theae).

The tea industry of the USSR produces black and green loose teas with rolled leaves and green and black pressed, or brick, teas. In India, China, and Japan yellow and red oolong teas are also manufactured. Caffeine, vitamin preparations (for example, a preparation of vitamin P in tablet form), and various medicinal preparations are produced from the by-products of the tea leaf. The oil from tea seeds is used in the cosmetic industry and the canning industry (as a substitute for olive oil); it is also used as a lubricant for precision instruments and in soap manufacture. The leaves are used as a seasoning in China and Japan and as salad greens in Burma.

In the USSR loose black tea is produced by curing, or withering, the leaf at temperatures of 40°-50°C. The decrease in water content makes the leaf pliable. The dried leaf is then rolled and fermented. Enzyme action oxidizes the bitter fractions of tannin, thereby forming pleasantly astringent tannin, as well as essential oils (with the aroma of rose, lemon, orange, or vanilla) and other substances that determine the taste, color, and aroma of the tea. After drying, the tea is graded into groups according to size of particles. The finished product, composed of a mixture of teas from the various groups, is packaged in 25-, 50-, 75-, 100-, and 125-gram sizes and is wrapped. Loose green tea is prepared almost the same way as black tea, but before drying the leaf is treated with live steam at a temperature of 100°C to destroy the enzymes and preserve the green color.

Black brick tea is made by pressing the dust and sittings from the grading of loose tea into bricks of 125 or 250 g. Green brick tea is produced from coarse leaf gathered in autumn after the principal harvest of flushes or in spring during pruning. The raw material is roasted to preserve the green color, rolled, stored in piles for fermentation, and then dried and pressed into 2-kg bricks.

A technique for producing yellow tea has been developed: A mixture of two parts raw material for loose black tea after fermentation and one part raw material for green tea after curing are dried, graded, and packaged. The first batch was released for sale in 1977. Tea grades are named for their place of manufacture. The following loose black teas are popular in the USSR: Büket Gruzii, Krasnodarskii Büket, Gruzinskii, Krasnodarskii (extra, first, and second grades). Imported teas from India and Sri Lanka are sold under the names Indiskii and Iseilonskii.

To prepare tea as a beverage, dry tea (approximately one teaspoon per glass) is poured into a teapot (preferably porcelain) that has been rinsed with boiling water. The pot is filled two-thirds full with freshly boiled water (white with bubbles but not rolling) and then covered with a napkin to minimize escape of aromatic substances. After steeping (3½ to 5 minutes for black tea, 8 to 10 minutes for green), the remaining third of the teapot is filled with boiling water. Properly brewed tea from loose black tea is golden in color and has a specific aroma (without the odor of steamed leaves); there is brown foam on the surface.

Tea contains caffeine, essential oils, and tannins, which account for its tonic and stimulating effect. Tea tannins have some vitamin-P activity and a slight bactericidal effect. Consumption of strong tea is not recommended for persons suffering from insomnia, hypertension, heart disease, gastric and duodenal ulcers, or neuroses.

Certain tea substitutes from plant material (linden, carrot, and fruit teas) and mixtures of medicinal herbs (diuretic teas and others) are also called teas.

REFERENCES

Chaevodstvo. Edited by T. K. Kvaratskhelia. Moscow, 1950.
Davitashvili, M. D. Chai nash gruzinskii. Moscow, 1970.
Bakhtadze, K. E. Biologicheskie osnovy kul’tury chaia. Tbilisi, 1971.
Xocholava, I. Ch’ais Tek’nologia. Tbilisi, 1972.

V. E. DZHAKELI, V. P. TSANAVA, and U. D. URUSHADZE

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