Drinking: Bumper harvest puts fair wind in the sails of port

Port producers in Portugal's Douro valley are smiling with relief at the prospect of a good vintage, which ends in the next few days. While Spanish sherry flounders, port is shedding its fusty image to win new enthusiasts. Elizabeth Nash treads the grapes to investigate a success story.

Some 35 of us stood in a vast granite tank, thigh deep in pungent purple glop, rhythmically stamping the day's cut of grapes into a spongy fluid that oozed between our toes and clung to our limbs like primeval slime.

Timing is vital for making port. You have less than 48 hours before the fermenting grape juice hits its optimum balance between alcohol and sugar, when you add brandy to stop the process, and settle the new port in vats. In that time the maximum colour and texture characteristic of Portugal's best known export must be extracted from the skins. And science has come up with no better method than the pressure of the human foot.

"Treading is still the best way of crushing the grapes while leaving the pips undamaged. It mixes up the skins with the juice and the body heat speeds the fermentation process," says Dominic Symington, sales director of his family's empire, that includes Graham's, Dow's and Warre's port. Only two family firms remain in a trade founded by 19th century British merchants, now dominated by multinational conglomerates. "For top quality vintage port, there is no substitute for treading."

Vesuvio estate, at the eastern end of the Douro more than 100 miles up river from Porto, is the jewel in the Symingtons' crown, dedicated to the production of vintage port, which forms a fraction of the region's output. The vines are perched on steep ravines of slatey soil that you would think too barren to support a blade of grass. But conditions here are perfect for port grapes.

"We are sheltered by mountains from the westerly winds and rain, so have hot dry summers that ripen the grapes and frosty winters that kill off diseases. The stony soil produces high sugar content and tough skins," Mr Symington says. An early heatwave followed by frosts threatened disaster, but a fine late August has saved this year's vintage.

The sun beats down on a gang of pickers moving along vines laden with fruit. Some have been coming for years to Vesuvio every autumn for the three-week vintage, from a village down the valley. The women cut the bunches and drop them into skips which the men load on to a truck. Amid murmured conversation and occasional gentle singing, the pace seems leisurely. A golden eagle wheels and wheels high in the still air, before heading off in slow motion to the mountains of Spain.

But the women's clippers move swiftly, and they fill their buckets in a blink. The men balance the heavy skips with a makeshift strap and a fibrous roll to protect their shoulders. They work from dawn to 6pm, stopping for breakfast and lunch. Then they tread from 8pm to 11pm. Sometimes they will be roused from their dormitories on the early 19th century estate to tread through the night.

By the time we clambered into the fragrant ooze to join them, they had been at it for three hours, regimented by a gang leader shouting out the rhythm as if orchestrating oarsmen in a trireme. Those on the end tapped advancing knees with a stick to keep the lines straight as they moved evenly across the tank or "lagar". Faces were weary by now, weatherbeaten compared to their creamy bare legs.

Only in the last hour - of "liberdade", or freedom - did the treaders break ranks to plunge and dance at will. I was taken into a lively churning two-step. The accordionist who traditionally provides the accompaniment had overslept and missed the truck rounding up the gang from their village, so we clapped and sang instead. In the old days the men (women used never to tread) were kept on their feet by copious supplies of alcohol. Today they are offered cups of grapejuice and cigarettes.

Vesuvio, like every port estate or "quinta", is limited to a strict quota it may produce, and for every one of the 120m bottles Portugal sells each year, the equivalent of three must be kept in reserve. Government-backed regulatory bodies rein back any temptation to overproduce, so demand constantly outstrips supply, keeping prices and quality high.

Port producers learned the lesson of Spanish sherry, whose overproduction prompted a catastrophic downward spiral of prices and quality. They realised that long-term prosperity lay in meticulous control of output year by year.

Next spring, barrels of this year's vintage will be taken to the ancient lodges in Porto's southern quarter of Vila Nova de Gaia, no longer by special boats piloted down river, but by lorry. Porto may seem trapped in the last century, with its crumbling waterfront slums and its art- nouveau coffee houses that would make Charles Rennie Macintosh weep for joy, but the wine to which it gave its name is forging ahead to the millennium.

"Business is going very well at the moment. We're going through a very successful period," Dominic Symington says. Breaking the stereotypes of gouty colonels and fusty Oxbridge colleges, nearly half Britain's port drinkers are under 44, and 47 per cent are women, he says. France remains the mass market for cheap port drunk chilled as an aperitif, but the big money is with the vintage quality sold overwhelmingly in Britain and increasingly in the US.

Port weathered the long Nineties recession with scarcely a blip - sales suffered more in the swinging Sixties - and economic revival is expected to encourage prosperous youngsters to pay the high price for the good stuff. The grape treaders of Vesuvio are likely to be plying their ancient trade for some years to come.