It’s common in whisky to discuss the previous contents of casks used in maturation.

You’ll have seen it on bottles – ‘bourbon cask’, ‘sherry cask’, ‘port cask’, ‘red wine cask’ and so on. And certainly the flavours of those previous constituents are extracted by maturing spirit and make a difference to the profile of the final whisky.

That being said, we feel that the type, the provenance, of the oak cask is every bit as important, and is, sadly, rather underdiscussed. So today let’s talk about France.

France’s oak forests are a marvel. There are an astonishing 34,000 square miles of them, as opposed to around 4,000 in the UK and less than 2,000 in Ireland. Their staggering extent is largely thanks to the Royal Navy, and you can read how that came about here.

Today many of those forests provide the French wine industry with oak for their thousands of barrels. But in fact French oak is coveted by winemakers around the world, from Rioja to Chile to Tuscany to Australia. Indeed despite America’s own vast forests of oak and significant coopering industry, many of the great estates of California choose French oak to house their best wines.

There are several reasons for this, but the first is simply that French and American oak are not simply from different countries, but are different species entirely. American white oak is Quercus Alba, whereas French oak is a mixture of Quercus Petraea and Quercus Robur.

The chemical and physical differences are significant. American oak is far higher in lactones than French oak – volatile, highly aromatic compounds which impart strong, sweet notes such as coconut and vanilla. French oak, meanwhile, has far higher concentrations of elagitannins – compounds which contribute structure and mouthfeel to a drink.

Most significantly, American oak is far, far higher in tyloses than its French cousin. Tyloses are the outgrowths of plant cells that protrude through the xylem and restrict water movement. The result being that American oak is far denser and less porous than Quercus Robur or Petraea.

To the American cooper this is a great boon. It means that logs of Quercus Alba can be sawn, rather than split, with the result that coopering in America became mechanisable on a vast scale. The French oak, meanwhile, is a far more troublesome creature to work with. Logs of Robur or Petraea cannot be sawn, but must be split along their grain; skilled and heavily involved work which allows the cooper to use no more than around twenty to twenty five per cent of the tree.

By its very nature this has two repercussions. Firstly, it significantly increases the price of a French oak barrel as opposed to an American. Secondly, it imposes an artisanal approach upon the cooper. There are no shortcuts – were the staves to be treated differently, the barrel would lose its water tightness.

This enforced attention to detail and care for craft feeds into the next, most vital stage of the coopering process, which is the seasoning of the staves. Seasoning is the practice of treating the freshly-cut oak such that it loses excess humidity and unpleasant aldehydes and softens the more astringent character of its elagitannins.

This can be done artificially and quickly by heating the oak in a kiln at fifty degrees celsius for a month, and at the more industrial American cooperages this is exactly what takes place. The disadvantage is that those harsher aldehydes are not fully broken down, tannins remain more astringent and bitter coumarin remains in higher concentration.

The best form of seasoning is to leave those fresh staves outside, exposed to the elements, for two, three, even as many as five years. During that time, not only are the harsher, more astringent and less pleasant compounds almost literally washed away through hydrolysis, but the slow process of air-drying breaks down lignin and methyloctalactone in the oak, reducing the more overt ‘woody’ aromas and increasing aromatic compounds such as eugenol (think cloves and toasty spice) and vanillin.

Our French oak barrels, having been allowed to season for years, are then toasted, rather than charred. This isn’t merely semantics. Toasting is a slower, gentler process of heating the barrel over an open flame for between five minutes (for a light toast) and fifteen minutes (for a heavier toast). Charring, meanwhile, blasts the oak with a far more furious flame for a matter of seconds.

The toasting process allows the fire to penetrate more deeply into the wood, further breaking down the lignin, increasing the lactones and the phenolics associated with toastiness and spice. The forcefulness of charring caramelises the wood sugars within oak, meaning far more impactful sweetness and caramel flavour when a drink is aged in them.

The best châteaus choose barrels made from split, long-seasoned, toasted French oak to mature their wines in. The character of the oak, and the way it has been treated, imparts a complex, gentle toasty spice without over-imposing on the natural character of the wine. Crucially, so far as we’re concerned, the toasting allows the wine to penetrate deep into the stave.

These are the casks to which we are referring when we talk about our Premium French Oak. Grown in the most scrupulously-tended forests of Europe, seasoned and toasted to the specifications of the world’s greatest wineries, with character always prioritised over efficiency.

The most expensive oak of all, but with casks as with spirit, if quality and flavour are the object, corners simply cannot be cut.