The herbal beverage known as green tea is made from the prepared leaves and leaf buds of the tea plant, botanical name Camellia sinensis (L.), which belongs to the plant family Theaceae. The plant is a large shrub with evergreen leaves and it is native to parts of eastern Asia and very extensively cultivated in that region. The same plant is used to prepare the common daily beverage black tea, which is processed by slow drying of the fresh leaves and then gradually allowing them to undergo fermentation. The process for the preparation of green tea is different, and this form of tea is far less popular as a daily beverage in the United States, in the case of green tea, the leaves of the plant are dried rapidly. The number of different cultivated varieties of the tea, and the different methods of preparation involved dictate certain important characteristics of the tea, on the average, the caffeine content of different teas ranges widely and differ slightly, these can fluctuate from about 1 per cent to more than 4 percent of different varieties of teas.
Some Asian countries have evolved traditional and elaborate ceremonies around the drinking of green tea, so much so, that these ceremonies have assumed the importance of a delicate art and have distinct cultural value. This can be seen as being similar to the way wine sampling or tasting is carried out in France. Finely brewed tea has its own connoisseurs, such individuals can tell what type of water needs to be used, and they dictate the kind of utensils which must be involved in the preparation of the tea and the approximate conditions in which particular teas must be prepared. Some of the green teas served in the Chinese mainland, are so incredibly strong for the palate that they are only served in thimble-sized and delicate cups. One of the benefits of caffeine in tea is that the caffeine compound constricts blood vessels inside the head, and for this reason the tea is able to calm the pain present in a throbbing and swollen head.
The Chinese have traditionally drunk different varieties of tea and the beverage has been associated with civilization in China since very early times. European introduction to the beverage did not take place, until the early 1600s when the Dutch introduced it into the continent. The tea as a beverage becomes very fashionable even though it was an expensive drink. The East India Company for example, enjoyed a monopoly over the tea trade in the United Kingdom and the British colonies, and had exclusive rights to tea trade with China until the year 1833. This policy of monopolizing the trade in tea was an attempt by the British government to levy a trade tax on all tea imports into the American colonies, a factor that lead to the Boston Tea Party of 1773 and eventually triggered the American war of independence. Tea is chiefly produced by two former British colonies today, India and Sri Lanka, formerly Ceylon. The stimulant alkaloid, caffeine is present in tea aside form another similar alkaloid thein. Tea as a generic term tea is also used as a description for many other local beverages and herbal drinks made using the leaves of a vast array of other plants.
Leaves and buds.
As an herbal measure, tea is helpful in the treatment of various infections affecting the digestive tract of patients. For example, the Indian traditional medical system known as Ayurveda, classifies tea as an herbal astringent, it is believed to induce sweating, and is used as a tonic for frayed nerves. Tea is also used for the treatment of various eye problems; it is used in the treatment of hemorrhoids, to treat physical tiredness and fatigue, and to bring down fever in patients. The leaves of the tea plant can also be used as a topical herbal measure for the external treatment, and to soothe a variety of insect bites and problems like sunburn.
Other medical uses
Habitat and cultivation
Tea is cultivated primarily in the Asian countries, and world's largest producers of tea are India, Sri Lanka, and China. In China, tea has been grown since the earliest times and the plant is native to this country.
The botanical name Camellia sinensis refers to the tea plant. However, the plant has a many different varieties, or subspecies which are also cultivated and used in a similar manner. At one time in history, there was significant confusion over whether one or more species of the tea plant existed in nature. However, this issue was cleared up in 1958, when a botanical international agreement was reached and now the prevailing classification is of one species having several varieties or subspecies, among these varieties, at least two types have very important commercial impact.
The tea plant is similar to the coffee plant, in that it is an evergreen tree or bush which grows chiefly in the tropics or in subtropical regions of the world. Tea plants require regular but moderate rainfall and the best teas grow in areas with elevated altitudes lying between 2,000 and 6,500 feet. The Assam tea is commercially the most cultivated of all varieties, the Assam tea, or var. assamica, has this distinction because it thrives best in tropical areas and has low resistance to cold climes. Yielding lower quantities of tea when compared to the Assam tea, the China tea, or var. sinensis, however is considered to produces a much more delicately flavored beverage and it is prized for this reason. The Chinese variety is also able to withstand much colder temperatures than the Assam variety at least for brief periods and thus can be grown at higher altitudes. Tea cultivation also reached the new world, during the 1800s, the China tea variety was cultivated as a major plant in the state of South Carolina, however, high labor costs made the plantations economically unsound and such attempts were abandoned. The plants still survive in this area to this day, though not cultivated in any large scale or commercially.
The Assam variety of the tea plant bears large leaves, often up to 10 inches long each; if the plant is left uncultivated it can reach a height of 50 feet easily. Tea varieties in China tea are much smaller, and have leaves up to 4-inches in length and the plants themselves have a natural height not exceeding 20 feet even when left untended. To facilitate the easy harvesting and plucking of the leaves, both varieties of tea plants are trimmed to waist height. To prepare the best teas, ideally only the young leaves and shoot buds are harvested by hand. This is a high skill requiring occupation, as plucking only the young leaves while keeping the plant healthy is difficult. Mechanical shearing of tea leaves is on the rise these days, so as bring down the high cost of labor, the quality of tea goes downhill if mechanical methods are used and this method produces a coarse tea which can vary in quality and may not be preferred by tea drinkers.
The results from a scientific research conducted on the tea in China suggest that consuming green tea can help in alleviating hepatitis in patients. As a result of another research carried out on tea, this time in 1990 by Japan based researchers, a connection between the certain chemical constituents present in tea and the inhibition of tooth decay was seen - these compounds present in the tea may probably help in the prevention of tooth decay.
At the same time, scientists at the University of California made the discovery that tea drinkers as a group experience lesser chances of hardening in the arteries when compared to people who regularly drink only coffee as a daily beverage. One reason suggested for these observations is that the caffeine in coffee may be chemically bound to some heavy oils; these often tend to elevate the total levels of serum cholesterol somewhat. This same effect on the body is not induced by either the dark or the green teas. Cholesterol levels may in fact be cut down significantly by the caffeine content present in both tea varieties in the large number of patients. At the same time, other benefits accrue to tea drinkers on the whole as the polyphenols present in the tea can act in concert with the body's supply of vitamins C and P; this combination effect will on the whole help in strengthening the walls of the blood vessels supplying the heart with blood.
The researches and studies documenting much of the actual health benefits of drinking green tea is mostly based on the amounts of green tea typically consumed in countries around Asia - this is about three cups of tea every day, which provides the drinker from 240 to 320 mg of polyphenols on average daily. Green tea can be brewed, using a single teaspoon of green tea leaves in combination with 250 ml or a cup of boiling water, allow the tea to steep into the water for three minutes and then drink. Standardized extracts of the green tea are now available in the form of tablets and capsules; these contain standardized extracts of the beneficial polyphenols, especially the effective compound known as EGCG, such forms of herbal remedy have become very easily available in many health food stores. At the same time, some of these extracts in the form of tablets and capsules are decaffeinated and can provide up to 97% polyphenol compounds to the tea drinker daily. Almost equal to drinking about four cups of green tea every day.
Side effects and cautions
The safety of consuming green tea is well known and side effects are insignificant. However, when large amounts of the tea are consumed, common adverse effects reported by patients have included the presence of conditions such as insomnia, nervousness and anxiety, and other nervous symptoms which are typically caused by the high caffeine content of the tea.
Post harvesting, plucked tea leaves are most frequently treated in either one of two ways during processing. Black tea is manufactured from about three-quarters of the total harvested leaves; these are destined for use and sale in the commercial beverage market. Green tea is processed from the other remaining quarter; this is the form of tea that is generally served in most Asian restaurants and especially Chinese ones. Black tea manufacture is the almost exclusively the preserve of large factories, this is due to the type of equipment required, and the processing time. On the other hand, most green tea is and can be produced by the small-scale workers, such as the family farm; however, this distinction is not accurate anymore, as green tea is also being manufactured in large scale and major factories these days. The processes involved in producing black tea, is to use freshly plucked leaves that are first withered and then slowly squeezed or minced so that the leaf releases its contained sap and juices. This is an important process, as the leaf sap has an enzyme - an organic catalyst compound - unique to tea called polyphenol oxidase, this enzyme causes the tea's colorless flavor producing chemicals to capture oxygen from the ambient air. This is an important step as the oxidizing reaction changes the chemical character of the tea leaves, turning them dark brown in the process.
The destruction of this oxidizing enzyme is a very important step during the production of green tea, and this must be accomplished before the enzyme can cause changes in the color of the tea and before it affects the flavor. Dry heat curing is used in China to stop this enzyme, while in Japan green tea is cured by steam heating - both countries are heavy consumers of green tea. Compared to black tea, the green tea on the whole tends to have a greater bitter flavor, because it contains these unoxidized flavor producing substances. The processing steps do not differ much from the processing involved in the manufacture of black tea following the completion of this initial step. The caffeine content of both types of tea is similar and each has almost identical amounts of the caffeine compound.
Tea is sorted for criteria such as size following the manufacturing process; it is graded according to quality and purged of stalks and dust, and then packed in foil lined chests, following which it is shipped to blenders or auctioneers for marketing. Typically each tea chest will contain between 30 kg and 60 kg of tea leaves. Tea bags are another way in which tea is marketed, and in North America, 90% or more of tea is packaged, marketed and used in this form.
Further processing may be required for a small portion of the processed tea, which is often further processed to remove the caffeine or used in the production of novelty items such as instant tea. Decaffeination of tea and coffee is very similar in terms of the methods utilized by the manufacturers, the majority of these processes often utilize the same chemical solvent, which is methylene chloride, and this solvent is used to extract the caffeine from the pre-moistened tea leaves resulting in decaffeinated tea.