Margaux, France | The architectural superstar Norman Foster has designed a farm shed and he is rather proud of it. But this is not just any old barn. It is the first building to be added to Chateau Margaux -- one of France's most venerable wine houses -- in two centuries.

The famous facade of the neo-Palladian mansion even adorns the label of its mythic red wines, some of the most prized and expensive in the world.

But unlike so many of the flashy signature buildings star architects like Foster are commissioned to design, you are not meant to notice the winery he has tucked so delicately under the eves of a barn.

"From a distance, it does not stand out. It is a background building. The counterpoint of the old and new is only revealed on closer inspection," Foster said. "It does not compete with the chateau."

As well it might. Such is the grandeur of the colonnaded Chateau Margaux that it is known as the "Versailles of the Medoc" after the Sun King Louis XIV's vast palace near Paris.

Nestling in the vineyards within a stone's throw of the Gironde estuary, the chateau and its cluster of pretty honey-coloured farm buildings was declared an historic monument in 1946.

- Space-age winery - 

With such architectural heritage at stake, its owner Corinne Mentzelopoulos, whose family have run Chateau Margaux for 35 years, described the project as "an unprecedented gamble". 

"The domain has never been expanded (since it was built in 1815). My father never dared. The only thing that was added was a cellar in 1982," she said.

But faced with having to adapt to new winemaking technology, Mentzelopoulos had no other choice but to expand if they were to keep producing 300,000 bottles a year -- more than a third of that the sought-after "premier grand cru" reds.

"We needed more (fermentation) tanks with different capacities that could cope with our different parcels of vines so we could experiment and make comparisons," Mentzelopoulos said.

The result is part barn, part pavilion with a traditional roof of orange-hued recycled local tiles held up by 12 stylised white steel "trees", inspired by the low, open-sided barns of the region.

Beset by similar problems,  other  legendary estates around Bordeaux in southwest France have also turned to star architects. 

Cheval Blanc, the most famous of the Saint-Emilions, began the trend by hiring the French architect Christian de Portzamparc to create a spectacular new winery that juts from the chateau like hand reaching out into the vines.

Beneath it's rippling space-age roof, the architect even designed the curved concrete tanks in which the wine is fermented.

Before Foster put pencil to paper, he spent a weekend walking around Chateau Margaux, absorbing what the French call the terroir. "I watched him soak up the existing architecture right down to the smallest detail," Mentzelopoulos said.

- 'No better Bordeaux' - 

Five years later, the barn which houses a new laboratory and 10 stainless steel wine tanks, is up and running, with a huge underground "vinotheque" of storage cellars dug alongside it.

"Yet you get the feeling that it was always there," said Mentzelopoulos, even though the design allows for the building to be easily adapted to cope with changes in wine-making technology.

Function must always trump both design and good looks in a winery, Mentzelopoulos insisted. It is all about producing wine that lives up to and even betters the vintages of which the future American president Thomas Jefferson sang the praises in the 1780s. 

For the polymath and wine loving Jefferson, Chateau Margaux was the best claret of all -- "there is no better bottle of Bordeaux," he declared. 

No matter how lovely the architecture, it can only be "a homage to the wine", said Mentzelopoulos. "The extraordinary thing here is our tradition, our know-how -- wine has been made here for 500 years and we are only a link in the chain."