It’s early in the afternoon, bright sunshine is filling the green valley and the river is gently flowing by. In between contented sighs, we savour delicious bacon bread and sip at fresh, cooling glasses of port. Hang on, something’s wrong here. Summer, daytime and port? Surely that sweet drink is something we’d only have once a year at Christmas, and after we’re stuffed to the gills at that. But out here in north Portugal’s Douro Valley, our group is discovering that if port – in this case white port – is a special occasion drink, there’s no reason why any time or day can’t be special.

This rugged yet beautiful valley, with its Mediterranean microclimate, is the birthplace and centre of global port production. As we sip away, basking in the sun that ripens all those grapes, and cooled by the gentle breeze that prevents the fruit becoming overripe, we quickly become grateful for the love/hate relationship between the English and the French. If not for their habit of bickering like two brothers over the TV remote, port would never have been invented, and this wine region – the world’s first demarcated and controlled by law – would probably not exist.

The drink arose more or less by accident in the 1600s, after the nations on either side of the English Channel became embroiled in yet another spat. Like the Freedom Fries eaters of modern America, the English authorities decided to strike a culinary blow against their opponents, introducing heavy taxes on French wines. The wine-guzzling English had a well-developed thirst for the stuff, however, and merchants eager to quench it were soon looking south to their old continental allies, Portugal. Experiments showed a touch of brandy helped the wine survive the journey north and, that by adding it before all the sugar had fermented, a delicious and unique sweet fortified wine was the result. Today, the English are still the world’s biggest consumers of premium port.

We enjoy white, ruby, vintage and late-bottled vintage ports while Rodrigo, from the Wine Academy at the Vintage House Hotel in Pinhão, explains the significance of each (see breakout). If we had any reservations as to why the drink from this corner of Portugal was so special, Rodrigo leaves us with little doubt. As he insists, port not from the Douro is simply not the same. We had a group from the US and they said they had drunk port before – the stuff they make in their country,” he says. “But as soon as they drank it here, they could tell the real port was superior. They do not have the soil and the environment is unique to this area.”

After lunch, and pleasantly relaxed after our crash course in port, we travel further back down along the Douro River. As we take in our surroundings, it becomes easy to appreciate just how impressed those merchants must have been by their early encounters with the small-scale wine being produced in north Portugal. For a start, the 17th century Douro River was untamed, punctuated by numerous difficult rapids and every shipment was at risk. Nor was, or is, this valley a gentle rolling countryside – although green, the hillsides are steep and rugged and hardly inviting to would-be growers.

A pleasant trip on the train from Pinhão to Porto reveals how one nation’s thirst for liquor transformed a rugged valley. Vineyards now cover the hills in all directions, at seemingly impossible inclines. Terraces have been hewn into the steep slopes, leaving the rugged hills looking like giant staircases. The heavy slate soil has been broken up, whether by hand or dynamite, leaving powdery, yellow dirt. Fortunately, as Rodrigo was keen to point out, all this effort creates perfect growing conditions – the slate soil is superb at retaining the rainfall and the dry stone terrace walls reflect maximum heat from the sun, promoting bumper crops.

Come harvest, between September 15 and October 15, the whole region comes alive with furious activity. Visitors can come and stay in the port house estates or quintas, and help with the hand picking of the grapes. Traditional ways are carefully followed throughout the process, so the mounds of ripened fruit are laid out in traditional lazares (stone troughs) and crushed by foot.

Our journey downriver finally ends when we reach Porto, the industrial centre of Portugal’s north, and the namesake for the fortified wine. It’s here that the Douro meets the Atlantic and splits the northern capital from Vila Nova de Gaia. As we take a short cruise out along the river, the view of Porto perched on top of a hill and soaking up the sun is priceless. Gaia faces it across the water with its collection of brazen wine company hoardings looking something like offspring of the Hollywood sign.

Naturally sheltered from the sun, Gaia is the perfect cool location for the port wine to sit and undergo the maturation process before export. Indeed, until 1987, port wasn’t port unless it first took time to sit and breathe at this one location.

Many of the wine storehouses offer tours of their cellars, and our group takes a look around Burmester, a company which has been exporting the wine for more than 250 years. Massive barrels, some more than 50 years old, bulge from holding the drink for so long. The ceiling of the cellar is stained a dark brown, which our guide explains, is the result of evaporation over many years. So much is lost ‘to the angels’ that the barrels can become half empty. But as we retire to the shop room for yet another tasting, my glass is definitely half full. Down here, deep in the cellar, and whatever time it is, it seems ripe for a delicious glass of port.”