“Red wine casks, such as cabernet sauvignon, syrah and barolo give more body to a whisky, and a lovely, silky, velvety, fruit note for example that comes through in the whisky. White wine has to have an extra dimension, such as sweetness, otherwise it can be difficult to get the influence in the whisky,” says Richard Paterson, Whyte & Mackay’s master blender.
So, what are the selection criteria?
“A light white wine will not have any impact, it must have enough body, and the wine should not be too thin or sharp. White wine casks contribute more sweetness, less dryness and a lower level of tannins than red wine casks. There is also some tartness, which is one step away from acidity,” says Graham Coull, Glen Moray’s distillery manager.
Being able to choose between varying styles of white wine means that master blenders also play the role of match-maker. “You have to think of the style of your malt whisky, whether light, medium or rich, and adjust your choice of wine cask accordingly. It’s how your individual malt will react with that particular cask,” says Richard.
But how does a master blender assess what a cask has to offer? Sampling the previous occupant, and nosing the cask provide opportunities, but to what extent can this predict the result of the rendezvous?
“It’s quite hard to correlate the impact of a wine cask on whisky, it’s not just the flavour of the wine in relation to the character of the whisky. It may not be a favourite wine when you taste it, but it can still have a positive influence on the whisky,” says Graham.
Glen Moray’s history of using white wine casks dates from a Chardonnay finish released in 1999.
“We use first fill Chardonnay casks for all finishes, with the malt initially aged in first fill Bourbon barrels. Chardonnay casks add layers of flavour including tropical fruits with ice-cream, on top of the creamy, vanilla, toffee notes from the Bourbon cask, and the two work well together,” says Graham.
“White wine casks may not give a huge influence, it’s a case of fine tuning, unless you’re using a dessert style such as Sauternes or Tokaji. The taste profile of Sauternes is the most sublime wine in the world to me, and an ideal partner for the classic profile of Glenmorangie. You’re relying on the influence of the tiny residue of wine within the staves, but this can add an ethereal quality to the whisky,” says Dr Bill Lumsden, director of distilling, whisky creation and whisky stocks, Glenmorangie.
This asset has established Sauternes casks as a classic choice for finishing malt whisky.
“Sauternes casks impart very nice citrus notes: lemons, oranges and lime, with hints of tropical fruit and creaminess, which enhances Tullibardine’s delicate floral, cereal character. This is a gradual change when finishing a mature malt, evident after about 9-12 months,” says Keith Geddes, master blender, Tullibardine.
However, ageing malts entirely in Sauternes casks remains a rarity.
“I wanted the honeyed sweetness and richness of Sauternes to marry with the Kilchoman character of citrus, sweetness and smoke. Of all the experimental casks, Sauternes was the most nerve-racking. It changed so much between three to five years, and was all over the place without structure or balance. I kept being told to be patient, but I’m not very patient. I’m very glad I waited, and it came round,” says Anthony Wills, founder, Kilchoman.
Casks with a provenance add to the production story, but how much more could be gained by stipulating the original winery?
“Most of us are now saying that unless we can use the owner’s name it doesn’t give full credit.
"Whisky lovers want to know the origin of the casks, and we only work with wineries who will let us use their name,” says Richard.
Cask selection is driving innovation, which naturally highlights the wood supply chain.
“Having a good relationship with cask suppliers is vital.
"A cask supplier can be commissioned to locate and supply specific cask types, such as white wine," says Keith Geddes.
"In terms of experimenting with a particular cask type, it’s difficult to source just one or two casks, and anyway, an experiment needs a certain number of casks in order to get a conclusive result,” Keith explains further.
White wine casks are usually 225 litres, with the interior toasted to varying degrees in order to ‘activate’ flavour compounds within the oak.
“The most important factor is the residue wine held in the pores of the wood, with the second being the level of toasting, as heavy toasting can give ‘carpenter’s shed’ notes,” says Richard.
Graham continues, “Using freshly emptied wine casks, which are still damp, is vital.
"If the cask dries out you won’t get even half the influence.
"That’s why it’s so important to have a third party to co-ordinate collection and shipping of casks so that they are fresh on arrival.”