Nature's Pharmacopeia: A World of Medicinal Plants
A terraced garden of young tea plants in Anxi County, Fujian, China. (Photograph by Winnie Lee)
The tea plant is a shrub or tree that bears simple, glossy green leaves and white-petaled flowers with multiple yellow stamens in the center (figure 11.1). Tea fruits are pale green, round, about the size of a small plum, and contain seeds that can be pressed to yield a commercially useful oil. Untended, tea can take the form of a tree reaching 10 to 15 meters in height; however, most tea in cultivation is pruned to a height around 1.5 meters. Tea plants require a few years of growth to become resilient enough to withstand harvesting, and plants can live for decades or centuries. Typically, the youngest leaves and leaf buds are plucked and processed into tea (figure 11.2). Successful plantations (called “gardens” or “estates”) can exist from sea level to 2000 meters in elevation, although the plants do best in tropical to subtropical mountain regions where there is regular rainfall and no frost (figure 11.3).1 The genus Camellia houses a handful of species native to Asia, including some planted as ornamental shrubs for their evergreen leaves and showy white, pink, or red flowers. The tea plant (C. sinensis) originated in the area of Southeast Asia where today’s China, India, and Burma (Myanmar) converge, and it is now cultivated in two varieties and their hybrids: China tea (var. sinensis) has thinner, narrower leaves and produces a more delicately flavored beverage than Assam tea (var. assamica).2
FIGURE 11.1 Tea: (top) plant of the China tea variety; (bottom) flower.
ORIGINS OF USE IN CHINA
By steeping tea leaves and other ingredients in boiled water, people in China produced a flavored, slightly sweet, stimulating beverage that was probably used medicinally before the time of the Han dynasty (206 B.C.E.–220 C.E.).3 The earliest account of tea preparation comes from the area now occupied by the borderlands between the central-western Chinese provinces of Sichuan, Hunan, and Hubei: it describes brewing roasted, powdered tea leaves with rice flour (Oryza sativa), ginger (Zingiber officinale), scallion (Allium spp.), and orange or tangerine peel (Citrus spp.).4 Through the sixth century, tea leaves often were steamed after plucking and pressed into dense cakes, which were baked and strung together on ropes through holes punched in their center.5 To brew the tea, the consumer chipped off and ground a portion of the hardened cake and steeped the resulting powder in water. As people developed new styles of tea preparation over many centuries, the new forms did not fully supplant the older ones, and as a result, today’s regional tea cultures share some features with ancient practices. For example, tea pressed into cakes or bricks is still a preferred form in parts of China, and grinding tea into a powder before steeping persists in Japan.
FIGURE 11.2 A tea bud and young leaves in Nilgiris District, India.
FIGURE 11.3 A tea garden in Hangzhou, China.
Tea diffused more deeply into the lives of the Chinese during the Tang dynasty (618–907), when it was widely adopted by Buddhist monks, who used it as an aid to meditation and study. As a medicinal substance of a certain rarity and value, tea entered the temple as a spiritual offering and found its way to the royal courts as tribute. It was also sold in markets and consumed by people of all walks of life.6 In an atmosphere of widely celebrated tea culture, the scholar Lu Yu (733–804) composed The Classic of Tea, a thorough account of tea cultivation and preparation in Tang-era China.7 In it, Lu describes what he considers the proper style of tea preparation, from the roasting and grinding of the tea cake, to the use of specialized utensils, to the technique for boiling the salted water, to the correct way to raise a froth in the beverage. (The foam is the “essence” of the tea, according to Lu.)8 As for additives popular during his time, such as scallion, ginger, jujube (Ziziphus jujuba), tangerine peel, dogwood berries (Cornus spp.), and mint leaves (Mentha spp.), Lu’s purism is unambiguous. “Such preparations are the swill of gutters and ditches,” he declared.9 As for its medicinal properties, Lu described tea as cooling, useful “when feeling hot, thirsty, depressed, suffering from headache, eye-ache, fatigue of the four limbs, or pains in the joints.”10
During the Song dynasty (960–1279), tea cakes were crushed and ground into a fine powder before being whisked into a thick froth. The tea was prepared by pouring unsalted, boiled water into cups individually, before frothing, rather than boiling the powder in a single vessel of salted water, as during the Tang.11 During the Ming (1368–1644) and Qing (1644–1911) dynasties, loose-leaf tea became popular, and processing techniques proliferated, resulting in many new flavors and aromas from the steeped tea leaves.12 As for additional condiments, they dwindled as improvements in tea handling produced ever more nuanced and flavorful brews. Still, tea scented with various types of flower petals became widely known, some of which remain common in modern China.13
As tea consumption expanded over the centuries, it wove itself into daily life. “Everyone, high and low, all drink tea, especially the farmers. Tea shops at the market places are numerous; merchants and travelers frequently exchange silk and lustrings [a type of glossy silk fabric] for tea,” wrote a government official in northern China in 1206.14 Teahouses were constructed in Chinese cities and towns, providing a venue for preparing and consuming tea in the company of friends and family, and also in the countryside, at particular scenic spots and near temples and shrines. Some teahouses were settings for quiet contemplation, and others were animated establishments of male entertainment; some teahouses served tea alone, and others offered tea, alcohol, and a complement of snacks and meals. The thirteenth-century author Wu Zimu describes certain recreational establishments in operation in the Northern Song capital of Kaifeng, where the “lanterns of tea shops burned all through the night.” In the Southern Song capital of Hangzhou, some teahouses provided lessons in playing musical instruments, served as venues for chatting with acquaintances, and offered other respectable forms of entertainment. In contrast, Wu also noted that “on the main street there are several teahouses with prostitutes on the second floor,” but these are “not places where a gentleman would set his foot.”15
The evolution of tea in China can be seen in light of its many roles: as a medicine, an aid to religious practice, a tribute passed from subject to sovereign, a medium of social bonding, and a substance around which material culture has been built. Over many centuries, tea passed along major trade routes to caravan crossroads and maritime ports, into the hands of foreign traders and deep into the domestic landscape. Tea served as a crucial commodity in the important horse trade that supplied the Chinese with Tibetan steeds and that lasted, nearly uninterrupted, from the eleventh through the seventeenth century.16 In Mongolia, where the compact and convenient brick tea suited the nomadic lifestyle, tea was accepted as a common currency, used to pay taxes and exchange for goods, a practice noted by European travelers as recently as the early twentieth century.17
THE SPREAD OF TEA: ALONG THE SILK ROAD AND BEYOND
It is likely that the first people to disseminate tea outside China were two Japanese Buddhist monks, who in 804 traveled to China to study Sanskrit and meditation at temples in Xi’an and Mount Tai. They returned to Japan having learned to drink tea and planted the first tea trees near Kyoto. “When I am not busy presiding over rituals,” one of them wrote, “I study the language of India with tea by my side.”18 Later, in the twelfth century, the monk Myōan Eisai (1141–1215) returned to Japan from China, where he had studied Zen Buddhism, and promulgated tea’s benefits for spiritual and physical health. Since tea in China at that time was customarily prepared by frothing powdered leaves in boiled water with a whisk, it is this form that Eisai advanced in his homeland.
Through contact with Mongols, Tibetans, and Persian and Arab traders along the Silk Road, the practice of tea drinking extended also to Central and western Asia, where unique tea customs conformed to local sensibilities and settings. For example, in Tibet and Mongolia, brick tea was preferred, sometimes with added salt and yak butter (Tibet) or cow, goat, or horse milk (Mongolia).19 By the seventeenth century, tea had reached Persia, where, according to a European observer, “[they] boil it [the tea] till the water hath got a bitterish taste and blackish color and add thereto fennel, aniseed, or cloves, and sugar.”20 Tea was an attractive social beverage in the Muslim world, where alcohol was prohibited, and it spread rapidly through the major centers of Islamic life.21 During the seventeenth century, tea also reached Russia, where it was warmly welcomed as a counteragent to the national beverage, vodka.22 Extensive and lucrative trading routes were established that transported vast quantities of tea from northern and central China throughout Asia, a heritage evidenced by a shared name for tea along the route (northern Chinese 茶, cha; Hindi chai; Russian чай, chai; Persian chai; Turkish çay).23
Tea was unknown in Europe until the mid-sixteenth century, when travelers to Persia returned bearing stories of a Chinese herb with medicinal properties. In 1610, a Portuguese writer who had spent time in India described “a little herb … proclaimed to be very beneficial, and prophylactic of those disorders which Chinese gluttony might provoke.”24 Just a few years later, Portuguese and Dutch traders arrived in southeastern coastal China and Taiwan with a commission to barter for tea. Important trading posts were established along the Chinese seaboard and elsewhere in Pacific Asia. In this way, the maritime route of tea commerce was established, one that supplied Europeans for centuries.25 In an interesting counterpart to the language built around the overland Silk Road from northern China, the word for tea in various European languages derives from the southeastern Chinese Min dialect (in Fujian 茶, pronounced tay, Dutch and German thee; French thé; Spanish té).26
Tea arrived in Britain by the 1650s and suited customers’ tastes at a time when another imported stimulant, coffee, was making its own important entry into the world market. By the 1730s, the coffee-drinking fashion had nearly subsided in Britain, and the tea custom became firmly established. While coffee was brought to English and Scottish ports at great cost via the Ottoman Empire, British merchant mariners provided Chinese tea in abundance, which ultimately reduced its cost and secured its rank as beverage of choice. England imported a mere 100 pounds of tea in 1680, but in 1700 was bringing in over 1 million pounds annually. By 1780, England imported 14 million pounds, which demonstrates the rapid commitment of its people to an Asian leaf produced half a world away.27 Meanwhile, in France, the opposite phenomenon occurred: strong imports of coffee and cacao together with weak imports of tea nearly eliminated tea from French beverage culture.28
Tea was likewise a mainstay of the American colonial lifestyle, and numerous importers provided the growing cities and villages with leaves to brew. The British East India Company served a primary role in transporting tea from China and distributing it throughout Britain and its colonies. In the rebellious American colonies, local tea smugglers and merchants sought to circumvent the overwhelming influence of the East India Company in colonial life by selling tea at a lower price than the East India Company could, skirting the taxes levied on the import and sale of all tea by the British Crown. As a result of this action, the East India Company suffered losses in the American colonial market. In 1773, the British government granted the East India Company the exclusive right to sell tea tax free in the colonies while still taxing American tea importers and sellers. As the duties on tea were significant, this tax law allowed the British company to undercut American merchants’ tea prices.
Responding to this perceived injustice, in December 1773 a band of Boston revolutionaries protested the tea-tax policy by storming three British merchant vessels and dumping more than 300 casks containing nearly 100,000 pounds of East India Company tea into Boston Harbor (figure 11.4). One of the most incendiary events of the American Revolution, the Boston Tea Party helped set a defiant American attitude and presaged the wholesale rejection of tea by the newly minted American nation as a British beverage.29 America’s history following the colonial period is generally that of a coffee-drinking people, with tea taking a more minor role in beverage culture.30
THE PROCESSING OF TEA
Much of the variation in the flavor, color, and medicinal properties of tea derives from alternative methods of processing the leaves.31 Tea leaves are harvested every one to two weeks during the growing season, which allows the desired young leaves and leaf buds to regrow from the stem for periodic plucking.32 The shape, size, color, and chemical composition of the fresh tea leaf are influenced by climate, soil type, and variety of plant, but nearly all differences in tea quality can be attributed to decisions made during harvesting and processing. For example, tea leaves that are hand plucked to include just a single leaf bud—a labor-intensive procedure—are considered to be of a very fine quality and delicacy. Plucking regimens that include one or two young leaves and the terminal bud are of incrementally decreasing quality. Hand-plucked shoots with older leaves are considered of lower quality still. Finally, harvesting leaves by machine is less discriminating and can yield tea of a relatively poor standard. In addition to the style of plucking, the processing of fresh leaves can influence the attributes of the final product.
FIGURE 11.4 Nathaniel Currier, The Destruction of Tea at Boston Harbor (1846). (Hand-colored lithograph; Library of Congress, Prints and Photographs Division, LC-USZC4-523)
Nearly all tea comes from young, vibrant green leaves (called the “flush”) of the tea plant, and differences in color, flavor, and aroma accrue during processing (figure 11.5).33 A minimally processed tea, white tea, consists of the youngest single buds and immature leaves of the plant, at a stage when they are coated with fine hairs. The hairy texture of the leaves often gives them a silvery, shiny appearance. In white-tea manufacturing, the leaves and buds are simply harvested and quickly dried. When brewed in boiled water, they produce a pale yellow color and mildly sweet, vegetal flavor.
To produce green tea, the leaves and buds are plucked and quickly steamed or pan-fried to prevent the breakdown of cellular components, rolled to crush open the leaves, and dried either naturally or by machine.34 Green tea, when brewed, produces an olive-green to slightly brown tea with a sweet, grassy, and mildly bitter flavor. In China and Japan, green tea is typically brewed from whole leaves; in Japan, it is also common to use powdered green tea (matcha).
Fresh leaves can also be harvested, lightly dried (withered), and then partially fermented by crushing them and allowing them to rest in a warm, humid chamber for several hours. Although the tea trade uses the term “fermentation,” the biological process is not the same as the one of the same name used in bread making and viticulture. The fermentation process in tea allows enzymes (biological catalysts) inside the leaves to begin degrading complex chemicals in the fresh leaf and produce new flavors via oxidation. After a certain amount of time, sometimes with intermediate rolling steps, a tea maker arrests fermentation by heating and drying the leaves. As a result of this process, called semifermentation, the leaves take on a greenish-brown color and brew to produce the oolong (wu long [black dragon])-style tea. Oolong teas have a complex flavor and aroma when brewed, often yielding a medium-brown color liquid. China and Taiwan manufacture numerous styles of oolong tea.
FIGURE 11.5 Different methods of tea processing result in the various styles of tea: (clockwise from top left) early-harvest white tea; unfermented green tea; mildly fermented oolong tea; highly fermented black tea; postfermented puer tea; roasted green tea, a Japanese specialty.
Alternatively, fresh leaves can be withered and then rolled and allowed to ferment for many hours in a warm, humid chamber to a dark, near-black hue before drying. The brewed tea is a reddish-brown color, with complex fruity, earthy, and sometimes astringent flavors. This style of highly fermented tea is known as black tea.35 Black tea is produced in large quantity in China, India, Sri Lanka, East Africa, and the Middle East.
In ancient China, tea makers compressed tea into bricks or cakes to preserve its freshness and allow for more convenient transport by caravan. This style of tea processing is still prevalent in the southwestern Chinese provinces of Sichuan and Yunnan, among others. Tea bricks can be made of poor-quality black tea compressed with rice paste as a binding agent. However, many of the more prized forms of bricks or cakes are produced from carefully selected tea leaves that are steam pressed into thick discs. The tea cakes then undergo a lengthy postfermentation process in which they are matured in a controlled environment, sometimes for many years, during which time further oxidation occurs and microorganisms are allowed to subtly change the chemistry of the product. This form of tea, particularly famous in Yunnan, is called puer (also written “pu-erh” and “pu’er”) and is esteemed for its ascribed medicinal properties.36 The long postfermentation process develops complex flavors in the tea.37 Puer teas have rich chemistries and mellow flavors generally lacking in bitterness and astringency. Unlike most other teas, which must be protected from the air and consumed within months to avoid stale and weak flavors, the flavors of properly stored puer tea improve with age, and thus fifty- and hundred-year-old puer bricks can reach high values in the marketplace (figure 11.6).38
PROCESSING OF TEA LEAVES
Notable Producing Regions
Youngest leaves early in the growing season; quickly dried
Leaves steamed or pan-fried, sometimes rolled, and dried
Lake Tai, Jiangsu (China)
Leaves withered, rolled or crushed, and fermented for several hours
Leaves withered, rolled or crushed, and fermented for 12–24 hours
Leaves withered, heated, rolled, often compressed into bricks, and post-fermented for months or years
In addition to the initial processing, the flavors of tea can be modified by roasting, as is common practice for some green and oolong teas. Also, as pioneered by the early Chinese, numerous contemporary tea cultures prefer tea flavored with additives. While white, green, oolong, black, and puer teas contain only leaves of the tea plant (C. sinensis), some styles of tea include mixtures of plant species to develop particular tastes and aromas. For example, in Britain, Earl Grey is a popular form that contains black tea with the oil of bergamot (Citrus aurantium ssp. bergamia), an Italian citrus tree. Jasmine tea, a northern China favorite, is usually produced by steeping a combination of green tea and flowers of the jasmine (Jasminum spp.) shrub.39 The tea brewed is lightly sweet and fragrant. In Japan, green tea can be mixed with toasted rice and steeped in boiled water to make a flavorful drink called genmaicha. In contrast to these examples, herbal teas do not contain C. sinensis leaves and therefore are not true teas but tisanes. Some such herbal teas are made from chrysanthemum (Chrysanthemum spp.), chamomile (Matricaria chamomilla), hibiscus (Hibiscus sabdariffa), and rose (Rosa spp.).
FIGURE 11.6 A variety of postfermented teas prepared loose and compressed into cakes, bricks, and other shapes for sale in a shop in Guangzhou, China.
FIGURE 11.7 A worker packaging crush-tear-curl tea at a tea factory in Nilgiris District, India.
In the present day, the tea industry is one of constant innovation, where new flavors and technologies compete to sate the thirst of discriminating and often thrifty consumers. One important transformation in tea consumption was the introduction of the tea bag, a fine cloth or paper sac in which tea leaves are sealed, making the steeping process more convenient. Invented around the turn of the twentieth century and first marketed by the British tea company Tetley in 1935, tea bags now account for nearly all the tea consumed in the West.40 Rather than loose-leaf tea, most of today’s tea is produced by an industrial technique developed in twentieth-century India and now deployed throughout the tea-growing world: a method called crush-tear-curl, frequently abbreviated CTC.41 In CTC processing, the fresh tea leaves, sometimes harvested by machine to reduce labor costs, are withered and then fed through a series of high-speed roller wheels that shred them into small pieces. In this way, they oxidize quickly, require no further processing, and are easily sorted and packed into tea bags or sold in bulk. Nearly all CTC product is a darkly colored and strongly (some say harshly) flavored tea that can be drunk with sugar or milk (figure 11.7).
THE CULTURE OF TEA
The worldwide spread of tea has given rise to numerous traditions that now help define nations. As societies integrated tea into their community practices, unique tea preferences evolved, colored by lore and equipped with a specialized suite of implements used to prepare and consume tea. In China and Japan, where tea has a particularly long history, the preparation of this beverage took on a special importance. During the Tang dynasty, Lu Yu’s The Classic of Tea conveyed the ways that tea connoisseurs paid close attention to the selection of water, leaves, and utensils to prepare tea, documenting the twenty-four accoutrements that he believed were key to tea preparation.42 Yet the various tea rituals and implements demonstrate tremendous adaptability, which has yielded countless variations of tea service, tea ceremony, and accompanying tea wares.
The ritualistic preparation and drinking of tea serves a valuable social role in forming bonds between participants. For example, tea has long been used to signify respect and cordiality in China, whether in the form of a tribute good from vassal to feudal lord in an earlier era or as a token of hospitality during a visit to someone’s residence, a practice that exists to this day. In China, guests to a home or an office are nearly always offered tea as a gesture of welcome. During a tea ceremony, a focus is placed on the precise movements of the tea master and on the aesthetics of the beverage produced, such that all guests are tied together in a singular activity. Over many years, the tea ceremony, at various levels of formality, has come to signify the formation of business and political links as well as family affiliation (figure 11.8). Indeed, an important event marking many Chinese weddings is the celebratory offering of tea between the new in-law families.
FIGURE 11.8 A tea-shop worker conducting a tea service in Fujian, China. (Photograph by Winnie Lee)
In Japan, tea preparation rituals became elevated forms of spiritual practice after being disseminated widely by Zen Buddhist monks during the twelfth and thirteenth centuries. Driven by the notion that suki (devotion to art) can lead to self-transcendence, religious scholars took up the tea ceremony as a way to regulate emotion, improve mindfulness, and ultimately achieve enlightenment.43 The resulting Japanese tea ceremony—governed by intense discipline, precise movements, and an elaborate code of conduct—coupled the consumption of a stimulating, rich, frothed powdered tea with a meditative, spiritually significant physical pursuit. In response to the perceived overemphasis on ritual rather than the tea itself, an eighteenth-century Zen monk created a simpler tea ceremony called sencha (boiled tea), in which attention to the water, leaves, and brewed tea prevailed. The form of bright-green, flavorful, delicate tea used in this ceremony remains treasured today, and despite the monk’s intended focus on the beverage to the exclusion of ceremonial pomp, sencha service gave way in time to its own specialized performance, replete with specially made implements and service ware (figure 11.9).44
While the diverse forms of ceremonial tea preparation have come to employ a tremendous variety of ritual performances and intangible social meaning, they have also generated an important industry in the fabrication of specialized tea service items. These products of human craft include bowls, cups, kettles, and pots of diverse designs and materials.
FIGURE 11.9 A Japanese woman with her teaware. (Photograph by Herbert George Ponting ; Library of Congress, Prints and Photographs Division, LC-USZ62-51044)
Where tea has spread outside East Asia, it has become incorporated into the social lives of people and been adapted to suit local tastes. Although tea plants were extant in the far northeastern reaches of India for many centuries, it was not until the British introduced large-scale tea cultivation in the nineteenth century that the Indians developed a widespread indigenous tea culture.45 Today, tea is both an important source of export revenue and a national drink. Tea served in India is usually black tea prepared sweetened and spiced (figure 11.10). The recipe for Indian tea is variable, containing black-tea leaves boiled in water or in water and milk, usually with sugar or honey added. The spices frequently include cardamom (Elettaria cardamomum), cinnamon (Cinnamomum spp.), clove (Syzygium aromaticum), black pepper (Piper nigrum), orange (Citrus spp.) peel, ginger, nutmeg (Myristica fragrans), and star anise (Illicium verum).46 Known in India as masala chai, this style of spiced tea has also become popular in the West. As India’s productive industry sent out large shipments of flavorful black tea to the seaports of the United Kingdom, the custom of tea drinking became firmly seated in the lives of the British people.
FIGURE 11.10 A streetside tea maker preparing masala chai for his eager customers in Kolkata, India. (Photograph by Winnie Lee)
In Britain, tea has become both a drink and a meal, in that the tea-drinking habit developed during the eighteenth century generated a daily event in which families and co-workers could rest and refresh.47 The British traditionally consume black tea, often flavored with bergamot or other additives, poured into porcelain teacups with a small amount of milk.48 The proteins in the milk bind to complex tannin compounds in the brewed tea, which both softens the astringency of the drink and reduces the amount of dark residue left on the inside surface of the teacup. Tea, often taken with sugar, provided a stimulating and energy-rich boost that helped fuel the increasingly industrial, and industrious, British lifestyle. The custom of “afternoon tea” in Britain is a midafternoon light meal accompanied by sandwiches or sweets; “high tea” is served in the early evening and in earlier times replaced a formal dinner, particularly among working families.49 In many parts of the former British Empire, the word “tea” refers as much to a meal as to a drink. Indeed, during routinely long cricket matches, mealtime tea breaks allow players, officials, and spectators to dine and rest before resuming play.
While Turkey had a leading role in the spread of coffee, within the past two centuries tea has become a national drink, thanks in part to the successful cultivation of tea in Turkey beginning in the nineteenth century. Turks generally drink black tea brewed strong with no additional flavorings, adding one or two cubes of sugar. Customary tea service is in small glass cups narrow in the middle and with flared tops, roughly in the shape of a tulip flower (figure 11.11).50 In Russia, black tea is preferred, and it is usually served with sugar alongside sweets such as chocolates and jams. Now a defining characteristic of Russian hospitality, the samovar (self-boiling) is a device present in many homes, a combined tea kettle and stove in which tea is kept heated all day, ready to welcome a guest with a soothing, stimulating beverage of kindness. Indeed, in these places and everywhere tea traveled, it integrated itself into local custom and spawned arts and artifacts that help to define regions.
FIGURE 11.11 Turkish tea served in a traditional tulip-shaped glass.
TEA IN THE TRADITIONAL MEDICINES OF ASIA AND EUROPE
In early China, tea was valued as an herbal drug of particular versatility. “Tea lightens the body and changes the bones,” wrote a Daoist master in the sixth century.51 In various accounts, tea was said to cure sores and ulcers, treat breathing troubles, reduce phlegm, and improve digestion.52 In twelfth-century Japan, the Buddhist monk Eisai wrote that the body requires a balance of bitter, sour, pungent, sweet, and salty flavors to harmonize the organs. Yet the Japanese diet dangerously lacked bitter ingredients. “Our country is full of sickly looking, skinny people, and this is simply because we do not drink tea,” Eisai explained. “Whenever one is in poor spirits, one should drink tea. This will put the heart in good order and dispel all illness.”53 Later, the Chinese herbalist Li Shizhen (1518–1593) composed a detailed account of tea’s medicinal properties in the framework of traditional medical scholarship. “Tea is bitter and cold, a yin among yin,” he declared; tea dampens the body’s internal fire so that “a clear qi can rise.”54 When Europeans learned of tea, they included it in their herbal pharmacy and set about explaining its properties.
The first reports of tea emerged in Europe during the sixteenth century, and firsthand accounts by missionaries and traders elaborated extensively on its purported medicinal effects. The Italian missionary to China Matteo Ricci (1552–1610) wrote that tea “is positively wholesome for many ailments if used often.”55 The French missionary Alexandre de Rhodes (1591–1660) agreed: “One of the things contributing to the great health of these peoples [the Chinese], who frequently reach extreme old age, is tay, which is commonly used throughout the Orient.”56 By 1641, the Dutch doctor Nikolas Dirx (1593–1674) had studied tea in great enough depth to exalt it in prose:
Nothing is comparable to this plant. Those who use it are for that reason, alone, exempt from all maladies and reach an extreme old age. Not only does it procure great vigor for their bodies, but it preserves them from gravel [kidney stones] and gallstones, headaches, colds, ophthalmia, catarrh, asthma, sluggishness of the stomach and intestinal troubles. It has the additional merit of preventing sleep and facilitating vigils, which makes it a great help to persons desiring to spend their nights writing or meditating.57
Among the first purveyors of tea in Europe were apothecaries and physicians, who praised its ability to regulate humors similar to bloodletting or laxatives—but less painfully.58
Entrepreneurs also lauded tea’s myriad benefits in terms familiar to patrons accustomed to considering the harmony of their body’s fluids in the Galenic framework of health. In 1660, for example, the London coffeehouse owner Thomas Garway promoted tea as a potent remedy in an advertisement. First, he spelled out that tea’s “quality is moderately hot, proper for Winter or Summer. The drink is declared to be most wholesome, preserving in perfect health until extreme Old Age.”59 According to Garway, tea “prevents and cures Agues, Surfets and Fevers, by infusing a fit quantity of the Leaf, thereby provoking a most gentle Vomit and breathing of the Pores.”60
As men of medicine and commerce alike advanced the cause of tea in Europe, it transformed from an exotic, foreign herb to a domestic necessity. During the eighteenth and nineteenth centuries, Europeans increasingly obtained tea from grocers rather than apothecaries and consumed it at home rather than in coffee houses.61 Countless advocates heralded the plant’s perceived health benefits, although a small number of detractors warned against it, such as the Scottish-French physician Daniel Duncan (1649–1735), whose enigmatic moralistic concern was tea’s “voluptuousness.” This property, he cautioned, “creates in us an Aversion to good Things … and an inclination to bad Things.”62 Nevertheless, tea effectively became part of the daily routines of many Europeans, and as early as 1712 a widely circulated materia medica, A Compleat History of Druggs, summarized tea’s effects, in the terminology of the day, as lightening the spirits, suppressing “vapours,” driving away drowsiness, improving digestion, and cleansing the blood, among others. But, importantly, this pharmacy manual noted: “The Leaf is more used for Pleasure in the Liquor we call Tea, than for any medicinal Purpose.”63
MECHANISM OF ACTION
The tea leaf and the beverage made from it contain a tremendous diversity of chemicals producing flavor, aroma, and other bioactive effects. Beyond the sheer complexity of compounds present in any tea, there is a great variability in the characteristics generated by growth conditions, harvesting, processing, and storage. Consequently, the best studies of the health-related properties of tea must take these numerous factors into account. Additionally, it is important to recognize that the chemicals present in the tea leaf and brewed liquid undergo changes in the human body that may further alter their structure and properties. Therefore, when evaluating the possible health effects of tea, researchers performing experiments in laboratory dishes and using test animals are cautious not to extend their findings to potential human outcomes without proper evidence. In short, biomedical research on the physiological properties of tea has produced a large body of data, but much more work needs to be done to account for the diversity of tea varieties and constituents.
In addition to caffeine, which tea leaves accrue to 2 to 4 percent of their weight, tea contains a number of other chemically related methylxanthines (figure 11.12), including theobromine (0.1–0.2 percent) and theophylline (around 0.05 percent).64 Together, these compounds account for tea’s stimulating properties, with a principal role ascribed to caffeine. Theophylline relaxes the lung’s bronchial passages, a characteristic that makes purified theophylline one of the more potent asthma medications available.65 Theophylline also contributes to tea’s diuretic effects.66 Beyond the roles of these chemicals, tea produces a variety of other compounds that are demonstrated to contribute to its physiological properties. Furthermore, tea contains theanine, a type of amino acid that accumulates to 1 to 3 percent of tea’s dry weight and is thought to produce a calming effect via the brain’s glutamate neurotransmitter system.67
FIGURE 11.12 Active principles of tea: the stimulants caffeine, theobromine, and theophylline; the antioxidant epigallocatechin-3-gallate (EGCG).
Many of tea’s purported medicinal effects derive from its chemicals that can reduce the oxidation state of cells and tissues of the body. Oxidation, a process by which sun exposure, toxins, or everyday “wear-and-tear” reduce the effectiveness of cellular biochemistry, is associated with diseases such as cancer and heart disease as well as the process of natural aging. Tea, like many plants, is rich in antioxidant chemicals that may counter the natural aging and disease-development processes.68 The antioxidant properties of tea are generally thought to be strongest in minimally processed green and white teas.69 During the processing of tea leaves into oolong or black-tea forms, the antioxidant chemicals in the leaves become oxidized themselves via natural enzymatic activity and exposure to air and heat and therefore less effective antioxidants.70 Because of this, many scientists studying the medicinal properties of tea use green-tea liquid, powder, or chemical extract as a focus of investigation.
The chief antioxidants in (green) tea are a family of molecules called catechins, of which epigal-locatechin-3-gallate (EGCG [see figure 11.12]) and epigallocatechin (EGC) are the most potent. Green-tea catechins have been demonstrated in test-tube experiments and small-scale clinical trials to inhibit the proliferation of cancer cells or reduce the incidence of a number of cancers and heart disease. In laboratory studies, EGCG was shown to reduce inflammation, which is associated with heart disease and immune conditions and treat stomach ulcers caused by the ulcer-associated bacterium Helicobacter pylori.71 The scientific data, however, lack large-scale clinical trials that might determine unequivocally whether the catechins themselves are responsible for any therapeutic effects of tea or whether other compounds are involved. It is worth recognizing also that the antioxidant properties of the tea beverage might not directly extend to the cells of the human body because exposure to the harsh environment of the stomach and intestine, metabolism by the liver, and passage into the body’s circulation can alter tea’s chemical functionalities. Furthermore, there are concerns that highly concentrated forms of green-tea extract, such as those sold as dietary supplements, might be toxic to the liver in some people, particularly if taken on an empty stomach.72
In addition to their antioxidant properties, tea’s complex polyphenolic compounds can bind to and coat cell surfaces and the teeth, protecting them from pathogens. With regard to dental health, there is some evidence that tea inhibits the growth of harmful bacteria through several mechanisms that change the chemical environment of the mouth, ultimately guarding the teeth against decay.73 The antimicrobial nature of tea polyphenols has also been harnessed in an ointment preparation sold as Veregen, effective against genital warts caused by human papillomavirus.74
In the more highly processed teas, especially those with a longer fermentation, the tannin composition is particularly rich. As research into tea’s properties continues, its health benefits and risks can be better understood, ultimately yielding insight into the wisdom of ancient practices and guiding the development of new therapies from a storied leaf.
From the mountain forests of southern Asia to homes around the world, the tea plant has convinced hundreds of millions of people to brew its simple green foliage into a stimulating medicinal beverage. Over the millennia, diverse cultures developed methods to process tea leaves into a rainbow of colored drinks and serve them with all sorts of additives. Tea is a medium of social bonding through Asia and Europe, and beyond, and it has changed the course of history in nations continents apart. As scientific investigation identifies the chemical basis of its medicinal properties, tea will certainly keep its place among the most useful and valuable plants in the centuries to come.