(Decanter) - The broad spectrum of flavours and aromas that toasted new oak can impart to wine is more than familiar, from vanilla and caramel to rich mocha and baking spices. But costing as much as £700 a piece, it would be hard to justify purchasing new oak barrels for their flavour alone. So what exactly is the role these expensive vessels play?

What is the role of oak barrels?

Oak fermentation for white wines

Many of the world’s greatest white wines ferment and mature in oak casks. It’s labour intensive, but for many winemakers, the benefits amply justify the trouble.

The barrels establish intimate contact between the wine and the yeasts that carry out fermentation. As sugar is transformed into alcohol, those yeasts die, sinking to the bottom of the barrel to form a layer of lees.

‘They scavenge oxygen, protecting the wine through fermentation and maturation,’ explains Pierre Boisson, rising star of Meursault.

As yeast cells in the lees break down – a process known as autolysis – they release desirable substances into the wine, including amino acids and polysaccharides, which improve flavour and texture, as well as glutathione, an important antioxidant