Part One — How an ancient medicinal leaf became the world’s daily drink

Tea is so familiar that we rarely stop to consider what it is doing. We drink it to wake up, to think more clearly, to settle after a meal, to warm ourselves and to create a moment of calm. These effects are not simply part of the ritual. Tea contains a remarkable mixture of natural compounds capable of influencing attention, mood, circulation, glucose metabolism, digestion and the body’s response to inflammatory and oxidative stress.

Modern research is investigating tea in cardiovascular health, metabolic regulation, the intestinal microbiome, cognitive ageing and protection of the skin. Yet many of these questions are not entirely new. For centuries, tea was valued as something that cleared the mind, relieved heaviness, supported digestion and helped preserve health.

To understand what tea may offer us today, we first need to understand what tea actually is—and how one medicinal leaf became so many different drinks.

The plant behind the cup

True tea comes from one evergreen species: Camellia sinensis. Left to grow naturally, it can become a small tree. On tea estates, it is repeatedly pruned into a low shrub to encourage the production of tender new shoots. The most valued harvest generally consists of the unopened bud and the first one or two young leaves—the familiar “two leaves and a bud.”

Two principal botanical varieties have shaped tea culture. Camellia sinensis var. sinensis has smaller leaves and tolerates cooler conditions. It is closely associated with the tea traditions of China and Japan. Camellia sinensis var. assamica has larger leaves and thrives in warmer, more humid regions. It became central to Assam and many other tropical tea-growing areas.

As with grapes, the variety is only the beginning. Altitude, soil, rainfall, shade, season, the age of the harvested leaf and the way it is processed all change the finished tea.

Green, white, black, oolong, pu-erh and matcha are therefore not different medicinal plants. They are different expressions of the same plant.

Tea before the teapot

According to Chinese legend, tea was discovered by the emperor and herbalist Shennong when leaves blew into a vessel of boiling water. The drink revived him, and tea entered the long history of Chinese medicine.

It is an evocative foundation story rather than a documented historical event. Archaeology gives us firmer evidence. Tea residues discovered among funerary offerings at the Han imperial mausoleum in Yangling show that tea was being consumed in China by the second century BCE. Related material found in western Tibet demonstrates that tea was already travelling considerable distances along early trade routes.

The earliest tea did not always resemble a modern infusion. A third-century Chinese account preserved in later tea literature describes leaves compressed into cakes, sometimes using rice paste as a binder. To prepare the drink, part of the cake was roasted, ground and covered with hot water. Spring onion, ginger and citrus peel could then be added. The result would have been bitter, aromatic and savoury—somewhere between tea and a seasoned herbal broth.

The same account associated tea with dispelling the effects of alcohol and preventing sleep. Tea was already being recognised by the way it changed alertness and bodily sensation, even though no one yet knew the names of caffeine or L-theanine.

Why tea was compressed into cakes

Freshly harvested tea leaves deteriorate quickly. Steaming, pounding, moulding and drying the leaves produced a compact material that could be stored, counted, transported and traded.

Tea cakes could be threaded together and carried over long distances. Compression became increasingly important to the imperial tribute system and to trade across China, Tibet and Central Asia.

These early cakes were not necessarily identical to modern pu-erh cakes. Contemporary pressed teas may contain recognisable whole leaves, while many early cakes were manufactured from steamed and pounded leaf material.

The rice paste mentioned in early descriptions appears to have helped bind coarser or older leaves into cakes. It should not be interpreted as proof that all early tea was a substantial grain broth.

More genuinely nourishing tea preparations developed in Tibet and Mongolia, where compressed tea was later combined with salt, butter or milk. These drinks supplied warmth, fluid and energy in cold, high-altitude environments—but they belong to their own regional history.

Lu Yu and the transformation of tea

By the Tang dynasty, tea had moved far beyond its regional origins. It was cultivated, traded and consumed across China. During the eighth century, Lu Yu composed the Chájīng, or The Classic of Tea. This extraordinary work described the plant, its cultivation and processing, the quality of water, the preparation of the drink and the utensils required to serve it.

Lu Yu described a much more refined way of preparing compressed tea. The cake was first roasted over a flame to refresh its aroma and remove moisture. It was then cooled, ground and sieved into a powder.

Water was heated in a cauldron. A little salt was added during the early stage of boiling, and the tea powder was introduced as the water approached a stronger boil. The prized surface foam was carefully preserved and distributed between the bowls.

Lu Yu accepted a small amount of salt, but disliked the popular practice of boiling tea with onions, ginger, jujube, citrus peel, dogwood fruit, mint and other aromatics. His criticism is valuable precisely because it confirms that such mixtures were familiar.

This marked an important change. Tea was moving away from being treated as one ingredient within a mixed functional broth and towards being appreciated for its own origin, fragrance, flavour and quality. Tea was becoming a discipline. Its value lay not only in its action upon the body, but also in the quality of attention involved in preparing it.

From boiled tea to whisked tea

During the Song dynasty, powdered tea was placed into a bowl, combined with hot water and whisked into a fine foam. Tea competitions judged the colour, texture and persistence of this foam. Preparation became technically demanding, aesthetically refined and closely connected with scholarship, poetry and social status.

This powdered-tea culture later influenced Japanese tea preparation. However, Japanese matcha did not simply preserve Song tea unchanged. It developed through its own methods of shading, steaming, processing and ceremonial practice.

Loose-leaf infusion became increasingly dominant in China during the Ming period. Instead of roasting and grinding a cake, the drinker placed dried leaves in a vessel and poured hot water over them. This change encouraged the development of new teapots, brewing vessels and styles of whole-leaf tea. It eventually created the preparation most familiar to us today.

Tea in Korea: preservation and transformation

Tea reached Korea through centuries of exchange with China involving plants, medicine, diplomacy, scholarship and Buddhist practice. Korean records describe established tea cultivation by the ninth century, although tea was known earlier. It became part of court life, religious offerings and monastic practice, as well as a drink associated with hospitality and cultivation of the mind. Korean tea culture developed its own restrained character, with close attention given to water, season, ceramics and the relationship between host and guest.

Korea is also important to the history of medicine. Korean physicians did not merely copy Chinese texts. They classified, tested and adapted inherited knowledge to Korea’s climate, plants and medical experience.

The Hyangyak jipseongbang, published in 1433, assembled thousands of prescriptions while emphasising medicinal materials available within Korea. The enormous Uibang yuchwi, compiled during the fifteenth century, preserved material from numerous earlier East Asian medical works. Some of those works later disappeared or now survive only through quotations preserved in Korea.

The Donguibogam, completed by Heo Jun and first published in 1613, created an enduring synthesis of medical theory, materia medica, prescriptions, diet and health preservation. Its 25 volumes are now recognised by UNESCO’s Memory of the World programme.

This parallel record became especially valuable after wars, political upheaval and the Cultural Revolution damaged particular archives and lines of medical transmission in China. Chinese medicine was not erased, but Korean and Japanese collections sometimes preserve different editions, prescriptions and methods that no longer survive in their original Chinese sources.

Korean medicine should therefore be understood both as an independent tradition and as an important witness to the wider history of East Asian medicine.

Korean food and medicine also developed a much broader meaning of the word cha. It can describe true green tea, but also roasted barley or rice water, powdered-grain drinks, medicinal roots and seeds, or fruits preserved in honey and stirred into hot water.

Roasted barley tea, or boricha, belongs principally to everyday food culture. It is served warm or chilled and often replaces plain water. Other preparations move closer to medicine.

Corn-silk tea has been used for the urinary system and fluid balance. Ginger tea is warming and digestive. Persimmon-leaf tea contains tannins, flavonoids and vitamin C. Omija, or schisandra tea, has traditional associations with the lungs, thirst, fatigue and the preservation of body fluids. Jujube, ginseng, balloon-flower root, goji, Job’s tears, roasted cassia seed, mugwort and lotus leaf may also be prepared in drink form.

There are also complex preparations such as ssanghwa-cha, which descends from a formal multi-herb decoction rather than an ordinary tea.

Korean tea culture therefore developed at the meeting point of hydration, nourishment, hospitality and medicine—but not every drink called cha comes from the tea plant, and not every traditional tea began as a medicine.

Tea in Japan

Tea was known in Japan by the early ninth century, but its wider cultivation and medical reputation developed gradually. A decisive figure was the monk Eisai, who returned from China with tea knowledge and seeds. His early thirteenth-century work, Kissa Yōjōki—usually translated as Drinking Tea for Health—presented tea as a means of nourishing life and preserving health.

Tea subsequently developed along several Japanese paths.

Steaming the freshly harvested leaves prevented extensive oxidation and preserved their fresh, green character. This eventually gave rise to teas such as sencha and gyokuro. Matcha followed a different process.Tea plants are shaded before harvest, changing the chemistry, colour and flavour of the developing leaf. Shading encourages a deeper green colour and helps create the characteristic balance of sweetness, savouriness and bitterness.

After harvesting, the leaves are steamed, dried to create tencha, stripped of coarse stems and veins, and finely ground. When we drink an ordinary infusion, most of the leaf is discarded. With matcha, the powdered leaf is suspended in water and consumed. It therefore delivers more total leaf material, but also potentially more caffeine and a more concentrated experience of the plant.

Matcha is not simply “strong green tea.” Its cultivation, processing and method of consumption make it a distinct form of tea.

Tea in India: an indigenous plant transformed by empire

India’s tea history is often told as though the British introduced an entirely foreign plant into the country. The real story is more complicated. Large-leaved tea plants grew naturally across Assam and neighbouring regions of Northeast India. Indigenous communities, particularly the Singpho, knew and used these leaves before British commercial cultivation began.

Their methods could involve roasting, drying or smoking the leaves before storing and boiling them. In 1823, the Singpho chief Bessa Gam showed Assam tea plants to the Scottish trader Robert Bruce. This encounter became part of the British narrative of the “discovery” of Indian tea—but the plant had not been discovered. Knowledge of it had been transferred from the people already using it to a colonial commercial system.

The Assam plant was eventually recognised as Camellia sinensis var. assamica. Its larger leaves and affinity for warm, humid conditions distinguished it from the smaller-leaved Chinese variety.

During the 1830s, the British began experimental planting and manufacture in Assam. The Assam Company was established in 1839, and the region developed into one of the world’s great centres of black-tea production.

This expansion created a vast international trade, but it was also built through colonial control of land and an often brutal plantation labour system. Workers were moved long distances under restrictive contracts, and women came to form a large proportion of the tea-garden workforce.

The history of Indian tea cannot be separated from their knowledge and labour.

Assam tea became known for its strength, depth, maltiness and ability to retain its character when combined with milk. These qualities later made it central to breakfast blends and Indian milk tea.

Darjeeling and the Himalayan leaf

Darjeeling followed a different path. During the 1840s, Chinese tea plants were introduced experimentally into the cool Himalayan foothills. At high altitude, slower growth, mist, marked changes in temperature and seasonal harvesting produced teas very different from those of the Assam plains.

The earliest spring harvests, known as first flush, are generally light, fresh and floral.

Second-flush Darjeeling is fuller and may develop the distinctive ripe-fruit or “muscatel” character for which the region became famous. Autumnal teas tend to be rounder, darker and softer.

Darjeeling demonstrates how profoundly landscape can change tea. Plant variety, harvest season, altitude and oxidation combine to create a drink that may bear little resemblance to a powerful low-grown Assam, even when both are sold as black tea.

India also developed important tea traditions in Nilgiri, Kangra, Dooars, Terai, Sikkim and other regions. Assam Orthodox, Darjeeling, Nilgiri Orthodox and Kangra are now recognised as distinct geographical indications.

From colonial export to the Indian cup

For much of the nineteenth century, Indian tea was grown principally as an export commodity. Large-scale domestic tea drinking developed later. Tea-industry campaigns during the twentieth century encouraged people to take tea at railway stations, factories, markets and roadside stalls. Indian households and tea sellers transformed the British style of milk-and-sugar tea by combining it with established Indian spices and preparation methods.

The result was not one fixed recipe, but an entire family of drinks now loosely called masala chai.

Chai simply means tea. Masala chai means spiced tea. Depending on region and household, it may contain fresh ginger, cardamom, cinnamon, clove, black pepper, fennel, nutmeg or other aromatics. The tea is generally simmered with water, milk and sugar rather than delicately infused and removed.

This produces a substantial drink in which the tannic strength of black tea is softened by milk, while the spices create warmth, aroma and digestive complexity.

Is masala chai an ancient Ayurvedic medicine?

This is frequently claimed, but the history is more interesting than the marketing. Ginger, cardamom, cinnamon, clove, fennel and black pepper all have long histories in Ayurveda. They are used to influence digestion, appetite, respiratory function and the handling of coldness, heaviness or stagnation. However, Camellia sinensis was not a central medicine in the foundational Ayurvedic texts. The familiar combination of black tea, milk, sugar and spices is not one ancient, standardised Ayurvedic prescription.

Masala chai is better understood as a comparatively modern tea drink constructed from much older Indian knowledge of spices. An Ayurvedic interpretation can still be useful. The spices may counter some of the cold, heavy qualities of milk, support digestion and alter the way the drink feels in the body. But the result depends upon the recipe.

A ginger- and black-pepper-rich chai is different from one dominated by cardamom and fennel. A lightly sweetened chai is metabolically different from a large drink containing several teaspoons of sugar. The medicinal intelligence lies in adapting the spices and preparation—not in assuming that every sweet masala chai is automatically therapeutic.

Tea in Nepal

Nepal’s tea history is closely connected with Darjeeling, but it should not be treated as an imitation of Indian tea. According to Nepal’s National Tea and Coffee Development Board, the first tea estate was established in Ilam in 1863, followed by a tea factory in 1878.

Commercial expansion remained slow for many decades, but tea gradually became an important crop across Nepal’s eastern hills. The high-growing districts of Ilam, Dhankuta, Panchthar and Terhathum lie close to Darjeeling but have their own soils, elevations, weather and communities of growers.

Nepal now produces two broad commercial styles. In the lower and warmer Terai, tea is frequently manufactured using the crush-tear-curl, or CTC, method. This produces small particles that infuse rapidly and create a strong liquor suitable for milk tea.

At higher elevations, producers make orthodox teas in which the leaves retain more of their structure. These include black, green, white and oolong styles, as well as increasingly experimental small-batch teas.

High-grown Nepali black teas can be floral, honeyed, fruity or gently muscatel. White and green teas may emphasise the tenderness of the young Himalayan leaf, while oolongs allow producers to explore different degrees of oxidation.

Nepal shows that tea categories are not permanently tied to one country. The same mountain garden can potentially produce white, green, oolong or black tea according to how the harvested leaf is handled.

Tea becomes a global drink

Tea reached European maritime traders during the sixteenth and seventeenth centuries. Dutch merchants helped establish it as a fashionable and expensive drink in Europe, while Portuguese connections influenced its arrival at the English court.

In Britain, tea moved from royal and aristocratic circles into coffee houses and eventually domestic life. Taxation made it valuable, smuggling made it widely available, and the East India Company turned it into a commodity of enormous political and economic importance.

The desire to control the tea trade helped drive British cultivation in India and contributed to the commercial conflicts surrounding opium and China.

Tea also continued travelling by land. It moved through Tibet, Mongolia, Central Asia, Persia and Russia, acquiring butter, salt, milk, sugar, jam, citrus and local herbs along the way. The plant remained Camellia sinensis, but every culture remade the drink.

How one leaf becomes many teas

Once a tea shoot is picked, enzymes inside the damaged leaf begin transforming its compounds through contact with oxygen. Tea makers control this process through withering, rolling, heating, drying, grinding, ageing and, in some teas, microbial fermentation.

White tea

White tea is gently withered and dried, with relatively little handling. It is usually delicate in flavour, although mature white teas can become deeper and more complex with age.

Green tea

Green tea is heated soon after harvesting to limit oxidation. Chinese green teas are commonly heated in pans, while Japanese green teas are generally steamed. This preserves their fresh character and more of the catechins found in the young leaf. Green teas range from light and floral to grassy, marine, toasted or gently bitter.

Yellow tea

Yellow tea is a relatively rare Chinese category. It begins rather like green tea but undergoes an additional controlled “yellowing” stage in which the warm leaves are wrapped or rested. This softens some of the grassy sharpness and produces a rounder, mellower character.

Oolong tea

Oolong is partially oxidised.

It covers an enormous range, from light, floral and almost green styles to darker, roasted teas with rich fruit, honey or woodland notes.

The category cannot be defined by one flavour or one level of oxidation. Some oolongs are closer to green tea, while others approach the depth of black tea.

Black tea

Black tea is allowed to oxidise extensively. During this process, many of the smaller catechins are transformed into theaflavins and other larger polyphenols that contribute to its amber-red colour, depth and astringency.

This transformation does not make black tea an inferior version of green tea. It gives black tea its own composition and biological activity. In Chinese terminology, what English speakers call black tea is generally called red tea because of the colour of the prepared liquid.

Dark tea and pu-erh

Dark teas are aged and transformed with the involvement of microorganisms. Pu-erh is the best-known example. Their earthy flavour and distinctive composition develop through microbial activity and continued ageing. Some are pressed into cakes or bricks and may continue changing for years.

Matcha

Matcha is produced from shaded green-tea leaves. The leaves are steamed, dried into tencha, stripped of coarse stems and veins, and finely ground. Because the powdered leaf is suspended in water and consumed, matcha provides more total leaf material than an ordinary filtered infusion.

Black tea and oolong are often described as “fermented,” but their principal transformation is enzymatic oxidation. Pu-erh and other dark teas undergo genuine microbial fermentation.

Kombucha is different again: it is made by fermenting an already prepared tea infusion with yeasts and bacteria.

Why processing matters to health

Processing changes far more than taste:

Green tea retains more of the smaller polyphenols found in the fresh leaf. During black-tea production, many of these combine to form the larger compounds that give black tea its colour and characteristic structure.

Oolong occupies a broad territory between the two. Dark-tea fermentation introduces microbial transformations, while matcha provides both the soluble infusion and the powdered leaf.

This is why it is misleading to ask which tea is universally “healthiest.” The more useful question is: what do we want from the tea, and when are we drinking it?

Tea for calm concentration

Tea naturally contains caffeine together with L-theanine, an amino acid strongly associated with the tea plant.

Caffeine promotes wakefulness. L-theanine appears to modify the quality of that stimulation, helping to explain why tea can support attention while feeling different from coffee. The result is often described as calm alertness: awake and attentive, but not necessarily overstimulated.

A recent analysis of controlled trials found that tea, L-theanine and the combination of L-theanine with caffeine can influence particular aspects of attention, mood and sleep. The response depends upon the preparation, dose, timing and individual sensitivity.

Green tea or a moderate serving of matcha may therefore be particularly suited to the morning or to periods of focused work. Matcha can contain a meaningful amount of caffeine and is not automatically gentle simply because it is green. A small traditionally prepared serving may be very different from a large café drink containing several teaspoons of powder.

Tea for cardiovascular and metabolic health

Habitual tea consumption has been associated with favourable cardiovascular patterns in large population studies from China and Japan. Researchers are examining how tea influences vascular function, blood pressure, cholesterol, glucose handling and inflammatory activity.

Tea polyphenols may interact with the cells lining the blood vessels, the metabolism of lipids and glucose, and the intestinal microorganisms that transform tea compounds after they are consumed.

This is less about expecting one cup to behave like a drug and more about understanding the possible value of a daily practice maintained over many years. Green tea is the most intensively researched, but black tea also contains biologically active polyphenols. The transformation of green-tea catechins during oxidation gives black tea a different chemical profile rather than removing its potential value.

How tea is served also matters. A regularly consumed infusion is different from a highly sweetened bottled tea or a large chai containing a considerable amount of sugar.

Tea, digestion and the microbiome

Tea has long been taken after food, particularly rich or oily meals. Its bitterness, astringency, aroma and warmth all contribute to the digestive experience. Contemporary research is examining how tea compounds interact with intestinal microorganisms and the gut barrier.

Not everything in tea is absorbed in the small intestine. Some polyphenols travel onwards to the colon, where the microbiota transform them into smaller metabolites.

The relationship works in both directions: tea can influence microbial activity, while the individual microbiome determines which tea-derived compounds become available to the body.

A small controlled study in Japan found that matcha consumption altered aspects of the faecal microbiota, including a reduction in Fusobacterium and an increase in Coprococcus. This is an emerging area that connects traditional digestive observations with modern microbial research.

Strong green tea, however, is not soothing for every stomach. Its caffeine and astringency can provoke nausea or aggravate reflux when it is highly concentrated or taken on an empty stomach.

A lighter infusion, a roasted green tea such as hojicha, a gently prepared oolong or tea taken with food may be better tolerated.

Tea and healthy ageing

Tea research increasingly extends beyond the simple idea of “antioxidants.” Scientists are examining how tea compounds influence inflammatory signalling, vascular ageing, glucose regulation, cellular stress responses and preservation of cognitive function.

A recent analysis of observational studies involving nearly 59,000 people found that higher green-tea consumption was associated with a lower occurrence of cognitive impairment.

This does not make tea a treatment for dementia. It does, however, support continued investigation of tea as one component of a long-term, health-supporting diet.

The most interesting question may not be whether tea can reverse ageing. It is whether decades of regular tea drinking can help create a metabolic, vascular and neurological environment in which healthier ageing is more likely.

Tea and the skin

Tea has repeatedly crossed between the cup and the dressing table. Green tea and tea extracts now appear in preparations intended for oily or blemish-prone skin, redness, scalp care and protection from environmental stress.

Tea polyphenols are being studied for their influence on inflammatory pathways, sebum, skin microorganisms and ultraviolet damage. In a controlled human trial, oral green-tea catechins provided specific protection to one component of the skin’s elastic-fibre network following an acute ultraviolet challenge.

Tea is not a substitute for sunscreen, but this finding helps explain why it has become relevant to research into photoageing and dermal resilience.

China, Korea and Japan also have histories of using tea infusions, tea powders and tea-derived residues in washing, bathing and topical preparations.

Modern cosmetic formulations may use green-tea extracts, tea-seed oil, fermented tea filtrates or purified tea compounds. These are not identical materials and should not be credited automatically with the same effects.

A later part of this series will examine tea on the skin in its own right—from historical washes and powdered preparations to modern research on inflammation, pigmentation, sebum and photoageing.

What happens when tea becomes kombucha?

Kombucha begins with tea, but it does not remain simply tea. Yeasts begin breaking down the added sugar, while acetic-acid bacteria transform fermentation products into organic acids. The microorganisms also build the floating cellulose-rich culture commonly called the “tea mushroom” or SCOBY.

During fermentation, the sugar concentration changes, new organic acids and microbial metabolites appear, tea polyphenols are transformed and the flavour becomes sharper and more complex.

Small amounts of alcohol may be produced. Caffeine usually remains, although its concentration can change.

Kombucha therefore becomes a new fermented preparation with properties determined by the original tea, the quantity of sugar, the microorganisms present, the temperature and the length of fermentation.

Its effects cannot simply be assumed from the original tea. Human research is beginning to investigate kombucha in relation to metabolism and intestinal health, but the composition of one kombucha can differ substantially from another.

Kombucha deserves its own article because it leads directly into our wider exploration of botanical and grain fermentation.

Rooibos: tea without the tea plant

Rooibos belongs in this series, but botanically it is not tea. It is made from Aspalathus linearis, a South African leguminous shrub. Rooibos is naturally caffeine-free and contains a different family of polyphenols, including aspalathin.

Its smooth, gently sweet character makes it particularly useful in the evening and for people who do not tolerate caffeine. Green rooibos is dried with minimal oxidation, while the familiar red rooibos develops its colour and flavour through oxidation.

Rooibos should not be described simply as a caffeine-free version of green tea. It is a separate medicinal and nutritional plant with its own cultural history, composition and developing field of research.

Choosing tea according to the moment

There is no need to identify one perfect tea. A thoughtfully chosen tea cabinet can serve several different purposes.

Morning or focused work

Green tea or matcha can support alertness with a more composed quality than many people experience with coffee.

Matcha is generally the more concentrated choice. A traditionally infused green tea offers greater control over strength and may feel gentler.

With breakfast

Black tea provides a fuller, more robust infusion. Tea is best separated from iron-rich meals or iron supplements when iron status is low because its polyphenols can reduce the absorption of non-haem iron.

After a rich meal

Oolong, pu-erh or another dark tea may provide a satisfying, gently bitter conclusion to a meal.

Individual digestive tolerance remains important, especially where reflux is present.

For a gentler afternoon cup

White tea or a lightly brewed green tea may offer a softer infusion, although white tea still contains caffeine.

When less caffeine is wanted

Roasted green teas such as hojicha are often lower in caffeine than matcha or teas made predominantly from young buds. Later infusions made from the same leaves may also be gentler, although caffeine extraction is variable.

In the evening

Naturally caffeine-free rooibos or a true herbal infusion is generally more appropriate than Camellia sinensis for people whose sleep is easily disturbed.

As a fermented drink

Kombucha should be understood as its own preparation rather than as a simple replacement for tea. Its residual sugar, acidity, alcohol content and microbial composition depend upon how it has been produced and stored.

Brewing changes the tea

The same leaves can produce a very different drink depending on how they are prepared.

More leaf, hotter water and a longer infusion generally extract more caffeine and more astringent compounds.

Green and white teas often benefit from cooler water and shorter brewing. Black and many dark teas tolerate higher temperatures and longer contact with water.

A tea that causes nausea or feels overly stimulating may not need to be abandoned completely. Using fewer leaves, cooler water or a shorter infusion can substantially change the experience.

Quality also matters. Loose whole-leaf tea may be infused more than once, with each infusion revealing a different part of the leaf’s character.

Tea is familiar—but never ordinary

Tea began at the meeting point of medicine, nourishment and ritual. It travelled through imperial courts, monasteries, pharmacies, mountain paths, caravan routes, colonial plantations, railway stations and domestic kitchens before becoming one of the most widely consumed drinks in the world. Every culture changed it.

China turned tea into a cultivated art. Korea preserved and transformed its medical and domestic uses. Japan developed matcha and its own disciplined tea traditions. Indigenous Assamese knowledge became the foundation of an enormous Indian industry. India combined strong black tea with milk and its ancient pharmacy of spices. Nepal created a distinctive new Himalayan tea landscape.

The familiarity of tea can make it seem insignificant. In reality, it offers a rare combination: a medicinal plant that can become part of ordinary life without losing its cultural depth or biological complexity.

The next parts of this series will examine the individual teas more closely: how white, green, yellow, oolong, black, matcha and fermented teas differ; what research is uncovering in China, Korea, Japan, India and beyond; how tea interacts with digestion and the microbiome; and how the leaf moved from the teacup into modern skincare.

Tea may be an everyday drink. It is also one of the world’s longest-running experiments in how a plant, taken regularly and intelligently, can become part of a healthier life.

References

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Lu Yu. The Classic of Tea. Eighth century.

Benn JA. Tea in China: A Religious and Cultural History. University of Hawai‘i Press; 2015.

UNESCO. Donguibogam: Principles and Practice of Eastern Medicine.

Academy of Korean Studies. Hyangyak jipseongbang.

Korea Heritage Service. Uibang yuchwi: Classified Collection of Medical Prescriptions.

Eisai. Kissa Yōjōki: Drinking Tea for Health. Thirteenth century.

Tea Board India. Tea-growing regions, geographical indications and the history of the Indian tea industry.

National Tea and Coffee Development Board Nepal. History of tea cultivation in Nepal.

Camfield DA, et al. Effects of tea, L-theanine and L-theanine with caffeine on cognition, sleep and mood in healthy participants: systematic review and meta-analysis of randomised controlled trials. 2025.

Zhou S, et al. The association between green tea consumption and cognitive function: a meta-analysis of current evidence. Neuroepidemiology. Published online 2025.

Teramoto M, et al. Green tea and coffee consumption and all-cause mortality among persons with and without stroke or myocardial infarction. Stroke. 2021;52:957–965.

Abe SK, et al. Green tea consumption and mortality in Japanese adults: the Japan Public Health Center-based prospective study. Annals of Epidemiology. 2015.

Wang X, et al. Tea consumption and the risk of atherosclerotic cardiovascular disease and all-cause mortality: the China-PAR project. European Journal of Preventive Cardiology. 2020;27:1956–1963.

Unno K, et al. A randomised, double-blinded study evaluating the effect of matcha green tea on human faecal microbiota. Journal of Clinical Biochemistry and Nutrition. 2023.

Charoenchon N, et al. Ultraviolet radiation-induced degradation of dermal extracellular matrix and protection by green tea catechins: a randomised controlled trial. Clinical and Experimental Dermatology. 2022;47:1314–1323.

Clinical note

Tea is a food and traditional medicinal beverage, not a replacement for medical treatment.

Caffeine sensitivity, reflux, pregnancy, iron deficiency and medication use can affect which tea, preparation and serving size are appropriate.

Concentrated green-tea extracts are not equivalent to traditionally prepared tea and require separate safety consideration.