Through a glass, darkly: Can vintage port appeal to a new generation?

The exuberant young Portuguese woman in front of me is, er – how best to put this? – shaking her booty vigorously, urging me to join her and her companions in a dancing conga line, the music is loud and the yelps and shouts of the dancers around me fill the humid air in an intoxicating late-night mix.

Our ability to perform the conga, which is followed by a slightly lewd version of the Birdie Song, is only partially inhibited by the fact we are all up to our knees – and in the case of my diminutive dancing companion, thighs – in crushed grape pulp, a sticky, inky mess that gets everywhere, as can be seen from the palm prints all over our T-shirts. It is both smooth and scratchy – from the stalks and pips – at the same time.

It is vendimia "harvest time" at the Quinta de Vargellas, the prime vineyard of the Taylor's Port company in the upper Douro Valley in northern Portugal. I'm taking part in probably the oldest tradition in wine-making – treading the grapes, a typical port mix of six grapes but mainly tinto nacional, tinto roriz and tinto franca. The winery has a wooden ceiling, is lined with traditional tiles, and as the music from a tinny little organ pounds out and the young dancers become more uninhibited, I feel the presence of Bacchus – God of both wine-making and ritual frenzy – very closely.

The treaders, mostly students and a few local vineyard workers, have already spent a long day picking in the baking heat on the steep, Douro hillsides and, for the last two hours, working to a rhythmic beat in arms linked, line formation, have been carefully and slowly treading the grapes in the lagare – rectangular granite vats – to ensure they all are crushed evenly. Then, at the sound of a whistle, they are released from their line, the organist starts and the dancing begins and, in another tradition, any visitors such as myself are obliged to join in.

It is a remarkable thought that these young students, earning just €20 a night, might have grown up and retired before some of the wine being trod on this warm September night actually gets drunk, on the plush dinner tables of London, Paris or Beijing, maybe 40 years from now, under the label of a Taylor's port. For treading is only reserved for the finest ports, which are allowed to age for many years before consumption.

But why treading? And why does it have to be done immediately after picking, I ask Alistair Robertson, 74, chairman of Taylor's, as, late on this sultry September evening, under a clear and starry night sky, he leads the party of visitors down the steep hill to the winery: "Quite simply because it is the best way of getting the colour and flavours out of the grapes in the shortest possible time. And it has to be done as soon as possible after picking to stop any immediate fermentation.'' When the clear grape spirit is added to the wine after two to three days' treading it swiftly arrests fermentation but preserves the tannic structure of the wine, a key act in allowing the intense, sweet flavours to develop in the years to come, says Robertson. You can drink a bottle of port from the same vintage every year for 20 years, and it will taste different every time.

Practices such as treading – although now only used in a small proportion of production – and long ageing, help make port, made only in Portugal in the world's oldest officially designated wine region, such a singular drink, surrounded by tradition and ritual.

Drinking port is not simple: while elsewhere in the wine trade, each harvest is termed a vintage, whether its good or bad, in port only certain years are "declared" a vintage – always on 23 April, St George's Day.

Its unique taste derives mostly from a combination of some of the 20 port grapes, ripened in the sunshine of the almost vertical Douro hillsides, which gives an intense, rich sweetness to the fruit; some have thick skins containing the tannins that help give port its long ageing potential.

Port blenders take wines from different years and vineyards to create the different styles. But time is all-important with fine wines: no one can say for certain, until probably some time next spring when the wine has developed a little, whether tonight's grapes are going to become part of a single quinta, a tawny or even a vintage year.

Port is also unusual in that most of the major brands are controlled by two companies – The Fladgate Partnership which owns Taylor's and Symington Family Estates – still run by the descendents of the British founders of the port trade, created in the 16th century when Britain developed a taste for Portuguese wine fortified with brandy. In an extraordinary demonstration of proprietorial grandeur, the Douro hillsides are emblazoned with large signs bearing names familiar from supermarket shelves and drinks cabinets: Cockburn's, Graham's, Dow's.

In Britain, consumption is split between those who buy one bottle of ruby or LBV each Christmas, enjoyed with the Stilton and walnuts – and more discerning individual drinkers, who buy a regular bottle or even a case of vintage or tawny port for their dinner tables. Premium port remains the drink of the upper classes and the landed gentry.

It is a tightly knit world. Robertson, born in Portugal to an English port trade family, inherited the Taylor business from his uncle, a descendent of the original 17th-century founders, in 1966. In 2000, he handed it over to his son-in-law, Adrian Bridge. His wife, Natasha, Robertson's eldest daughter, is head blender. Head winemaker is David Guimaraens, whose father, Bruce, was also a key figure in the company. Even the organist inherited the job from his father more than 20 years ago.

Over at the Symington estate, seven family members run the company, most members of the 13th generation in the port trade. When they bought Graham's and Smith Woodhouse in the 1970s, they were re-acquiring companies of which their ancestors had once been part. They have their own Vargellas: the Quinta do Vesuvio.

That sense of generational custody applies also to some of the most carefully tended vineyards in the world. "We pick the grapes our parents and grandparents planted and we plant the vines our children and grandchildren will pick,'' said Antonio Magalhaes, Taylor's head of viticulture.

Yet amid all this continuity and tradition, there are growing pressures on port producers, although sales overall are holding up. Portugal's economy is in turmoil, costs are rising everywhere and EU subsidies favour table wines, which has prompted many Douro producers to start making table wines. At the same time, a long-running subsidy that has kept clear spirit prices down is soon to end, putting further pressure on costs. In Britain, the after dinner digestif is less popular, there is a health-based bias against high-alcohol wines – most ports are about 20 per cent – and port remains largely the preserve of an older, diminishing generation, not quite fashionable with the young, like vodka, or with foodies, in the same way sherry has become.

Simon Field, of up-market wine merchants Berry Bros and Rudd, says: "Port is struggling a little bit. Vintage ports hold up well, particularly when there is a declaration, such as 2009, but the rest of the market is under threat. It is a wonderful product of course, but is still only being bought by the same loyal buyers – and any younger ones coming to our tastings tend to be their children.''

And almost always their sons. Although Waitrose reports an increase in sales for white and tawny ports among younger consumers, port remains a middle class, middle-aged, male preserve. In an effort to tap into a younger, more female market, Croft, founded in 1588, has launched Croft Pink, and although it has not grabbed public attention, it is popular as a cocktail mixer.

Back at Quinta de Vargellas, the customs continue.

It's midnight and Robertson's guests are drifting off to bed before he suddenly remembers something – after treading, he says, we should have drunk our port by the house pool, soaking our purple-stained feet. "Come on,'' he says, grabbing the decanter. "It's a tradition....''

Port styles

Tawny port

Blended from different vintages and vineyards, tawnys are aged in wooden barrels, transforming them into a golden brown hue and a mellow, nutty flavour. The official ages are 10, 20, 30 and "over 40" years. Can command very high prices.

Vintage Port

A vintage is "declared" every few years when it is deemed that the grapes have produced exceptional quality wine and bottle aged for up to 40 years or longer. Vintage ports are only around two per cent of total production. The prime after-dinner port or to accompany cheese, preferably stilton. A single quinta vintage port comes from one named vineyard. A crusted port is blended from several vintages and bottle-aged.

Late Bottled Vintage

Made from vintage port left for four to six years in the barrel, rather than the minimum two and a half years. A relatively recent addition to port styles, first sold in the Sixties. Lighter bodied and designed to be drunk young, although some can age further in the bottle.

Ruby port

The cheapest and most widely produced type of port, from lesser vineyards or years, not usually given a year of production. Sold and drunk relatively young because it will not normallyimprove with age. A reserve port is a slightly more refined ruby, from a better producer or vineyard.

White Port

Medium dry to sweet and made from white grapes. Drunk chilled over ice, with tonic and accompanied by local almonds, white port is the traditional aperitif of the Douro.

Pink/Rose Port

The newest port style, first produced by Croft in 2008; other producers have followed suit. Made like rosé table wine, with the red grape skins removed early in fermentation. Lighter and drunk chilled, it is aimed at a younger market and can form the base of a wide varietyof cocktails.