Wine connoisseurs may turn up their noses in disgust but, according to analytical chemists in Spain, producers of Rioja should abandon their age-old tradition of using barrels made from French and US oak, and try Spanish oak instead.

The researchers, led by Estrella Cadahia from the Centro de Investigacion Forestal in Madrid, want to find a new use for wood from Spanish forests and so set out to show that wine aged in Spanish oak is just as good as that aged in French oak. After all, they note, Spanish oak comes from the same species of tree as the French oak, Quercus robur or Quercus petraea .

Rioja is generally aged in barrels made from French oak but US oak is also used, especially for ageing cheaper ranges of the wine, according to Pascal Chatonnet, a French wine consultant. The US exports Quercus alba for wine barrels.

The researchers matured Rioja wine in a series of barrels for a couple of years, occasionally taking samples for analysis. After nine months in barrels, the wines shared a similar chemical composition. After almost two years, however, strong flavour differences emerged. As the researchers expected, wine from the Spanish and French oak barrels tasted similar but that from the US oak barrel, whose chemical composition had changed markedly, did not.

The researchers found that one particular compound, b -methyl- g -octalactone, which was not present in the original wine, developed as the wine matured. The compound's cis and trans isomers have very different sensory properties; the cis isomer smells and tastes of fresh oak while the trans isomer has more of a coconut flavour.

Wines aged in US oak developed more of the cis isomer than those aged in French or Spanish oaks, a finding that leads the researchers to suggest that measuring levels of the isomers could be a good way to differentiate between the barrel types. Manufacturers should think twice before choosing US oak, warn Cadahia and her team, because it can give wines an 'excessive woody character', or a 'resinous smell', which they say can mask the fruity character of the wine and spoil its bouquet.

But it could still be a long time before the Spanish wine industry accepts home-grown oak for its Rioja barrels. According to Chatonnet, the main problem is the lack of high quality wood. 

Emma Davies