Bruce Ginsberg can recall many life-changing cups of tea. There were the ones he had as a boy on his father's farm on the South African Cape where Rooibos, the world's only vitalising, caffeine-free tea was first discovered and cultivated. There were the ones he drank in the Daitoku-ji monastery in Kyoto where he went as an 18-year-old to study Zen Buddhism alongside monks and Beat poets. And there was the cup - perhaps the sharpest and brightest he has ever tasted - he had early one spring morning in the back room of an antiquarian bookseller in Bloomsbury. It was a green tea with an unlikely, straggly-looking leaf that had been bought by the excited proprietor from a Swiss dealer. The dealer, it turned out, had found it by chance in a remote Chinese village whose name, despite Ginsberg's subsequent prompting, he would not, for anything, disclose.

It is those kinds of discovery that Ginsberg himself dreams of. He is an 18th-century plantsman, intrepid and curious and always grinning, transported into the future. Tea - its culture, its variety, its possibilities - is what infuses him with his great appetite for life, and for adventure. It is why he comes to China each year, and travels up into the hills in search of new leaves to bring back to the English market. And it is why he was sitting opposite me in early May in Hangzhou, China's heavenly city, where the sun was slowly dipping below the mountains that surround the West Lake, which has been the principal inspiration for Chinese poets and artists for a thousand years.

Hangzhou was, for Marco Polo, who visited in the 13th century, without any question 'the most noble city and the best that is in the world'. It was then a place of canals and stone bridges, a hundred willow-pattern plates come to life. A single narrow man-made causeway crossed the lake, punctuated by temples and tea houses and ornamental gardens, the originals of all garden landscapes in the world. On the lake itself there were gondola-like pleasure boats, with tables set for elaborate dinner; courtesans would drift by the shore, singing siren-songs to the young men of the city. At that time no other place on earth had such a concentration of wealth. The Sung dynasty had chosen Hangzhou as its imperial capital and the merchants and scholar-gentlemen and hermit poets who lived around the lakeside had days of cultivated ease.

A good deal of that wealth was based in tea. Zen Buddhist monks in the region's monasteries had first used tea as an aid to meditation. The Hangzhou poet Lu Yu brought tea drinking and its attendant ceremonies into the mainstream of culture in the eighth century. Marco Polo took tea in the afternoons with the emperor and talked about the rival beauties of Venice as he gazed out across the West Lake. For a long time after his visit, however, Westerners were not encouraged to visit the walled city. When the traveller Robert Fortune came in the 19th century, it was in disguise. Dressed as a merchant, he was carried into the town on a sedan chair, and was served tea by monks without giving himself away, marvelling at the opulence and beauty of the place.

In the previous couple of days, spent exploring the city, I'd had a strong sense that in these days of the 'Chinese miracle' a lot of that opulence was about to return. Hangzhou, which suffered as a place of decadence during the long years of the Cultural Revolution, was recently ranked in a business survey as the most dynamic city in the world. A bullet train will soon link it with Shanghai, cutting the journey time from two hours to 40 minutes. One side of the lake is now forested by skyscrapers, but the causeway, the gardens, the pleasure boats and some of the tea houses remain.

While in Hangzhou I had taken to getting up at five in the morning, brewing a quick cup of the local green tea and then walking along the lakeshore with the mist hanging low in the cool morning air. The walkways that surrounded the lake were at that time thronging with people doing their own thing. Some were walking backwards, to strengthen different muscles and offer a change of perspective; occasionally they bumped into each other and laughed. Many hundreds were doing tai chi, and a few more solitary types were energetically shadow boxing or practising martial arts on the islands of the lake. Older people in ones and twos walked together slapping life into their shoulders and their thighs, barking out sudden raucous cries, creating an unlikely dawn chorus. Around one bend I came upon a riverside square in which maybe 200 couples were serenely waltzing to Strauss on a CD player. Almost all of these people had a flask of green tea with them or somewhere beside them. They tended to keep that tea going all day, refreshing the same bright green leaves with hot water.

The local tea, Lungching, improves, gets lighter and more brisk, after the first cup. Yu Lu, in his manual The Classic of Tea, suggested the first cup was for smell, the second for flavour. People in Hangzhou do not talk about drinking tea, but about eating it; it is both sustenance and comfort. Some people in the early morning sat in the shade by the shore playing mahjong or Chinese checkers, slurping occasionally at their tea in which the Lungching leaves floated. Others contemplated the lake over the rim of their cup, waiting for the long, slender leaves with their single attached bud to settle in the hot water.

As Bruce Ginsberg drank in this same view, and we sipped our tea on that late afternoon, he explained how he got here. His grandfather came from an old Russian tea family, he said, with an import company that had been trading since 1830. Benjamin Ginsberg had a wanderlust, however, that seems genetic. As a young man he took himself off to a remote part of the Cape to make his fortune.

Rooibos was a wild plant growing in the Wilderness Mountains with which the farmers made a rough brew out in the fields. Ginsberg's grandfather became fascinated with this plant, which looked and tasted like normal tea but was attributed locally with wide-ranging health-giving properties (later it was discovered to be extremely rich in antioxidants, useful in protecting against cancer and heart disease). He carried some down from the mountains on the back of a donkey and developed curing techniques for it, based on old Chinese methods and some of his family knowledge. He then set about finding a way to propagate it and encouraged some local farmers to start growing it. He launched his brand successfully on the local market. Ginsberg's father thus inherited a little tea company, and started the first dedicated plantation with the aim of turning Rooibos into an international drink.

Bruce Ginsberg was born into this dynasty, but like his grandfather - and unlike his father who was rooted in the local soil, a boxer and a rugby player in the Cape - he wanted to see something of the world. He took himself off to Asia, imagining he would become a painter. Zen was a buzz word and Gary Snyder, one of the original Beat poets, was living in one of the monasteries in Kyoto, so Ginsberg pitched up there, washing floors and cleaning lavatories, hoping for artistic enlightenment. The Japanese, he recalls, were quite perplexed why there was this sudden interest in what they did, particularly given it was such an unbelievably rigorous physical regime.

'Beginning meditation is like being a hunting dog having a bad dream,' he said. 'You sit still hour after hour. You follow your life breath by breath and hang in there as best you can.' The novice monks on retreat would endure this sitting for maybe 17 hours a day. If they moved, they would be beaten by a master with a long stick. The only thing that sustained them in this time would be the cups of tea that were served every hour or so. Ginsberg himself quickly ended up with very sore knees but a renewed interest in the qualities of tea.

'I always had a close relationship with plants,' he said. 'As a result of my years in Asia, I began to think I learned how to achieve some sort of rapture by being properly engaged with nature. Tea was very much a part of that.' The tea culture had been imported to the Japanese monastery from the hills near Hangzhou. Bodhidharma, the first patriarch of Zen, faced a wall there in meditation for nine years. The legend is that he spent such a long time staring at that wall that his eyelashes fell out and tea bushes sprouted from them.

Whatever the truth, Ginsberg says, it was an intimate part of the life he had immersed himself in. The slight caffeine kept you alert while the tea also had a soothing effect, the two principles of meditation. 'It is the same, you might say, for those Brits who sat in bomb shelters brewing their tea during the war,' he suggested. 'There is something about tea that gets you ready for action but also keeps you calm.' As Gary Snyder, Ginsberg's fellow Zen novitiate, wrote:

There are those who love to get dirty and fix things,
They drink coffee at dawn, beer after work.
And those who stay clean, just appreciate things,
At breakfast they have milk and juice at night.
There are those who do both, they drink tea.

With some of that idea in mind Ginsberg returned to South Africa, where he set about helping to run the family farm, hoping to bring Rooibos to the world. After six years of this, the old desire to wander returned, however, and he agreed with his father that he would go to London and spread the word in England. He placed himself under the discipline of a Zen teacher in St John's Wood and tried to get the British to start drinking the family brew. On one occasion he and his wife served 17,000 cups of Rooibos over a couple of days at a Buddhist gathering in London.

When the Rooibos started to take off, and after his father had sold some of his interest in the farm, Ginsberg sought to develop a new range of interesting teas, based on all the things he knew. 'I hesitate to use the word evangelical,' he says, 'but I thought it might be a way of bringing a bit more fun into the world; make people a little bit more relaxed. However bad the tea is that people are currently drinking, they still feel a bit of that. A housewife will tell you, or a builder, that a cup of tea represents a space where they can have some little bit of quiet to themselves. I wanted, in a small way, to see if I could extend that feeling, with quality teas.'

The tea village of Meijia lies a few miles outside Hangzhou. Chou En-lai lived here as a young man. The tea fields rise in steps from the valley and workers in coolie hats fan out from dawn to pick painstakingly the green tips of the bushes. On his way down from the fields one morning we met a man here on a bicycle with two panniers of tea leaves. Strapped to the back of the bike was a songbird in an ornate cage; the bird, he explained, kept him company while he worked. Further down the hill I talked to Zhao, who was 63 and was picking tea alongside her daughter. These few fields belonged to her family. She would work maybe 10 hours a day here, depending on the season, alongside the other pickers. In a day in high spring season each of them might pick a kilo of tea, for which they would be paid the equivalent of £4.

The tea here is organic, almost by default, since few of the farmers use pesticides. The prices for the best first flush of Lungching in the markets can reach £1,000 a kilo. The expanding middle class in China means there is more demand than ever for high-quality teas, and Lungching is considered among the finest. Twenty kilos of leaves, roasted by hand in a large, very hot wok, produces one kilo of tea.

On his open porch in the village, the tea master, Mei, who is Zhao's husband, sits on a stool by his wok. He has sat by that wok for 50 years, and his hands know exactly how to move the tea to establish its optimum flavour. In the spring season Mei produces 50 kilos in this way, each kilo of leaves having being hand-roasted for a couple of hours. Mei sells the tea to the market for maybe £200 a kilo. When I shook his hand it was hard and smooth and warmed by the wok, like sun-baked leather.

We sat outside his little house, after a while, drinking his wonderful tea in the sunshine. As a young man, Mei had met his wife in the fields here, he said. When I asked him, through a translator, what he made of the changes in China in recent years, he seemed to have no understanding of the question. Eventually he said, 'tea stays the same', and laughed. His daughter and son-in-law lived in his house and helped at harvest time. For the rest of the year Xie, the son-in-law, worked in Shanghai on the building sites that are everywhere in that city. I wondered of him if he imagined his own son to be roasting tea in the future like his father-in-law. He said no, he would like his son to graduate from a top university, perhaps in America. He would like him to see the world beyond these fields.

In cities like Shanghai we had seen the clash of these two versions of China even more dramatically. Tea culture in that city is under threat from the advance of Western coffee franchises. There are now 47 Starbucks in Shanghai. Even so, at the tea market on the Nanking Road, business was pretty much as it had always been. Over the road, squatters in tin shacks were protesting their rights while their homes were being demolished around them to build yet more skyscrapers, but the tea traders continued unaffected. The market stretched for 300 yards and, on each side of a narrow passage, traders in tiny stalls were hand-rolling jasmine or scooping oolong and Lungching and tiny rolled pellets of 'gunpowder' brought in from farms like the one we had seen at Meijia and all around eastern China. Each village has a different tea in the way that each hamlet of Burgundy will have its own wine; the array is dizzying and so are some of the prices: up to £100 for a little packet of leaves (That sounds a lot, perhaps, until you think of the story from one auction last year. Lungching means 'Dragon well'; the original dragon well is up in the hills outside Hangzhou, where there are 300-year-old tea bushes once reserved for the use of the Emperor Qianlong. Last year half a kilo of leaves from these plants was bought for £52,000; presumably they made no ordinary cuppa).

Zheijiang University in Hangzhou is, I was told, quite modest by Chinese standards. It has 50,000 students and a campus-like small city. Professor Shuying Gong arrived one morning on her bike, straight-backed as Mary Poppins, outside the department of tea sciences and led us into her laboratory. Having walked down the Nanking Road it was hard to imagine anyone knowing all the tea in China, but Professor Gong is someone who does. In her lab, first things first, she put the kettle on. On one wall was a series of metal cabinets full of tea caddies, and pots, like a Damien Hirst installation.

Professor Gong accepts 50 or more students each year on a four-year masters course in tea. For this morning's lesson, along one bench she had set up a long row of metal tins. She picked one up, batch 403, and shook it with a circular motion. The tea magically graded itself: big leaves to the centre, smaller ones to the outside. Professor Gong peered at it, looking for the curl and shape of the leaves, assessing the colour, pulling at particular tea grains with a long pair of tweezers and holding them up to the light. The leaves made little shapes like Chinese characters on the metal tray, and she tried to read them.

There are, she suggested to me, about 8,000 tea varieties in China, and she could identify most of them - if not their grower, then at least their geography - by taste and appearance. She had become a tea expert by accident. Students were simply assigned a course when she started university, but she developed a taste for it.

She then measured out three grams of each tea in her sample, warmed her cup with thimblefuls of boiling water, then added water at 85 degrees, the optimum temperature, letting the tea steep for four minutes before straining each cup to leave a row of liquids ranging in colour from palest green to light brown. She went along the row smelling them. 'Lungching, last year's crop,' she said of one, 'the old smell is coming out now.' Or 'char-smoked lapsang'. After this she slurped each tea off a Chinese spoon, drawing it through her teeth to get the range of flavours, letting it settle on different parts of her tongue. Tasters are not allowed to wear perfume; if she has a cold, she can't work. 'This one,' she says of an oolong, 'feels like ants crawling on your skin.'

I wondered if she kept in her head the best cup of tea she had ever tasted. 'There have been a few,' she said. One time, she was a judge in the national tea tasting, in which each province of China submits its three finest teas. 'Although we are not allowed to have personal preferences as tasters, we should always be objective; one of the winners, an oolong, has always stayed with me in my head,' she said; and she laughed giddily at her little act of rebellion.

In the tea museum of Hangzhou there are many tales of gunpowder, tea trees and pots. There are also some of the many folkloric claims that the Chinese make for tea. Lu Yu said tea had five functions: refreshing, keeping the head cool, relaxing, detoxifying and curing boils. Traditionally, according to ancient custom, there are 'seven matters related to the starting of family life: firewood, rice, salt, oil, soy sauce, vinegar and tea'. Tea was used as a drug before it entered Chinese life: 'No Emperor Wei Di's drug pills are needed if one drinks seven cups of Lu Tong's tea.' And, this is one you hear often in Hangzhou: 'If you have a problem, solve it in a tea house.'

Bruce Ginsberg would go along with a lot of that, even if he despairs a little of the way tea drinking in Britain has gone since the invention of the teabag, and the imperatives of supermarkets. 'The average tea bag spends 14 seconds in the pot,' he explained, surrounded by the paraphernalia of Chinese tea drinking in a cool tea house in Hangzhou, where the tea menu ran to a dozen pages, on my last night in the city. 'Black tea has become highly mechanised at every stage of production,' he went on, studying the green leaves in his glass of Lungching. 'The essential interaction between the grower and the roaster is lost. If you look at the records of 18th-century England it seems likely that half the tea that was drunk was green tea and half was semi-fermented tea which we might have called black tea but which would not have been anything like as astringent as the teas that we now have. All tea would have looked green in the cup. Tate & Lyle for one, however, realised that tea might be an excellent carrier for vast amounts of sugar, so they encouraged tea with a strong bitter taste.'

In the 1800s Britain had 100,000 licensed tea dealers. There are now probably 5,000 supermarkets and a limited number of corner shops. Even 50 years ago large town grocers would do their own blending, and take pride in particular combinations. Even though all the big tea companies now produce speciality teas, the quality, Ginsberg believes, is still diminishing. 'Supermarkets require tighter and tighter margins, so some of the flavour is inevitably lost as companies look for cheaper blends. We require milk and sugar because the tea is so bitter but that should never be the case, and that is far removed from the drink that is understood in parts of the world where tea is still revered. We need,' he said, sitting by the West Lake where it all began, 'to find a way of going back to the spirit when the whole act of drinking tea was a ritual based on the elaborate arrangement of utensils.' He set some of these out between us: 'You listened to the water boiling, you opened your tea caddy, you spooned the tea into your China pot, you added the water at the perfect temperature, and so on. You waited. And while you waited you talked, and you had a jolly good time. Tea is the princess of all plants. We need to go back to treating it with reverence.'

I wondered if he thought that his own company, Dragonfly Tea, could make the British start to think about tea again in the way that the Chinese still do. He said he was not sure whether the company will grow that large, though he will continue to do his bit, without ever forgetting quite why he is doing it.

'But you know,' he said, 'I'm 60 this year. I'd love to spend say a month thinking about the colour green...' In the meantime, until that month came along, he would content himself trying to find more perfect teas of all colours: green, yellow, black and white. The following morning he was off early to search for a rare Keemun tea high in the mystical Huangshan mountains, which he believed was the secret of the original Victorian English Breakfast. 'The thing about me is that I am still into the childish excitement of it all,' he said, draining his Lungching. 'I just can't wait.'

· Tim Adams stayed at the Pudong Shangri-La and Shangri-La Hotel, Hangzhou, www.shangri-la.com. For details of Dragonfly tea, go to www.dragonflyteas.com