Small Fortunes: Could a technique from the Cognac-makers' playbook help make whiskies taste better?

From petites eaux to slow dilution, taking a lead from Cognac production is an interesting proposition when it
comes to whisky
By Millie Milliken
Louis XIII cellar master Baptiste Loiseau
Louis XIII cellar master Baptiste Loiseau
During a crisp day back in January, I headed up to Derbyshire the day before White Peak Distillery launched its inaugural Wire Works single malt whisky. Co-founders Max and Claire Vaughan and distillery manager Dave Symes were hosting a small group of journalists in their unassuming and beautiful distillery to unveil its first bottling. It was a momentous occasion – and one which came with a side serving of intrigue.

On our walk towards the warehouse, we came across a barrel that the team were starting to do some experimenting with. It turns out that Max, Claire and the team were in the very formative stages of playing around with petites eaux – French for ‘small waters’ – a spirit-dilution practice historically associated with Cognac. “In 2021, we had some discussion around the practice of using petites eaux in Cognac and thought it would be interesting to trial some similar concepts in whisky as part of a vatting," said Max.

There isn’t much literature surrounding the use of petites eaux. In his book Cognac (1986), Nicholas Faith wrote that petites eaux is made by putting water into an old cask, pulling some of the alcohol out of the wood and ending up at around 20–30% ABV after six months. Others describe petites eaux simply as a mix of Cognac and water, or even as a mix of water and very old eau de vie that has already dropped below the 40% ABV minimum strength.

Either way, this 'Cognac-flavoured water' is then used to dilute still-maturing spirit , as part of an ongoing process that sees a gradual increase in volume and reduction in strength of spirit in the cask.

The fundamental idea behind petites eaux is that complexity can be added to a maturing spirit by introducing some (albeit diluted) characteristics from the old cask and its previous (usually old and richly flavoured) contents. Meanwhile, the slow, in-cask dilution both allows the spirit to unlock elements in the oak that are better extracted at lower ABVs, while also minimising the chance of 'shocking' the spirit with a significant dilution at time of bottling. Adding water to any spirit creates an exothermic reaction and the theory goes that significant jumps in dilution can lead to the loss of delicate and desirable volatile aromatics. Conversely, slow dilution can lead to more complex spirits in the long run.

Interestingly, petites eaux aren't used by all Cognac houses (Hine, Louis XIII and Camus, for example, don’t use the method) and, when they are utilised, it is something that is done on a case-by-case basis. “It really depends on the vision, needs and style of every house and whether they choose to use these petites eaux or not,” explained Louis XIII cellar master Baptiste Loiseau. For Camus, demineralised water, distilled water and reverse osmosis water is preferred for dilution, and the latter is the choice at Hine, too.

Though Cognac and whisky have a growing relationship – countless distilleries, such as Glenfarclas, The Glenlivet and Mackmyra, have been using ex-Cognac casks on a growing scale for ageing and finishing whiskies – mirroring the use of petites eaux isn’t common. A more involved but comparable process (using heat, water and agitation) is practised in the US to extract spirit from used casks for proofing down products like Jim Beam Devil's Cut. However, the aim of the US method is to recoup alcohol that would otherwise be lost to boost production output, rather than to impart additional complexity. Importantly, those extracted 'waters' are blended with barrel proof whiskey at time of vatting, rather than added to maturing casks.

Indeed, it's the practice of slow dilution in the cask that is often seen as most valuable to Cognac producers, and cellar masters often reduce the ABV a couple of degrees at a time. Frédéric Dezauzier, global brand ambassador for Camus Cognac, explained the merits of diluting gradually: “The development of very high-end products requires a practice of gradual reduction with distilled, osmose, or demineralised water carried out over several decades. This practice is generally carried out in small structures such as family houses… [and] only offers advantages over time, maturation and [with] regular tastings.”

This is the part of the process that the White Peak team are most interested in. "We have been casking at varying ABVs since we started out to better understand oak extract and the interaction with our spirit, so the petites eaux trial is essentially an extension of an area we’ve been investigating for some time," Max continued.

To this end, the White Peak team disgorged aged spirit that was originally casked in first-fill oak over three years ago and then added demineralised water to obtain a resulting lower ABV before re-casking in first-fill oak. “The plan is this lower ABV spirit will spend a period of time in cask to extract some different oak characteristics,” Max added. In the future, the plan will be to use petites eaux as part of a vatting and build in the nuances of flavour and aroma. As it stands, White Peak is the only UK distillery I’ve heard of that's doing this.

In particular, slow dilution is something that Vaughan is hoping to roll out across all of White Peak’s Wire Works whisky range. “For every release of Wire Works Whisky where we dilute to a bottled ABV below cask strength, we always do so gradually over an extended period of time, typically over one to two weeks. The theory behind slow proofing has been well covered by others and we do think that reducing any ‘spirit shock’ benefits the final bottled whisky.”

Adoption of techniques used in France is something that distilleries like White Peak can use to stand out from the pack. With innovation in whisky getting more and more nuanced, it’s certainly a talking point, and I can't wait to taste the result.