Hamish Smith explores the distilling world in search of Angel’s Treasure.

I’m going to assume, with some degree of confidence, that you’ve heard of the Angel’s Share. Such a romantic notion the first time you hear it, so ear-witheringly boring by the hundredth. But within this yarn of divine evaporation is a little detail rarely aired. And that is the make-up of what evaporates through the barrels’ pores into the atmosphere.

You see, given the right conditions – such as at Metaxa’s cellars in Greece – air can be choosy. “That’s the Angels’ [sic] Treasure,” Huity Konstantinidou, global communications director of Metaxa, points out as we snake around the Greek spirit’s cellars, pausing at one particular barrel. “The angels are very generous – they leave behind blends that are very concentrated.”

She’s referring to the effect by which a dry atmosphere causes water to evaporate from the barrel at a faster rate than usual, creating a more concentrated liquid. The Metaxa master Costas Raptis (pictured) has been observing the phenomenon here for many years – on tasting the liquid, he had the idea to capture it, naming the expression Metaxa Angels’ Treasure.

At the Metaxa warehouse in Attica, Greece, the humidity in certain corners of the cellar can be lower than 50%. Raptis’ deputy Konstantinos Kalpaxidis explains: “Because the humidity is low, there is a tendency for the water in the barrel to go through the staves and replace the missing humidity. Because there is a lack of water on one side and an abundance on the other, there is an osmatic pressure.”

He compares this osmatic effect to that of drying clothes – they dry quicker in dry, rather than humid, conditions. The evaporation of spirits is, of course, impacted by a number of other conditions – temperature, air movement and the particulars of the barrel and its contents – but there is a rule of thumb when it comes to humidity.

Andrea Wilson, Michter’s master of maturation in Kentucky, wrestles with hot and humid summers and cold and dry winters, so is in tune with the effects. “In general, in highly humid environments the alcohol evaporates and the whiskey strength decreases, but in drier environments the water evaporates first, so what we see is concentration of the whiskey over time and a higher strength as the product ages.”

The concentration of flavours and aromas sounds like a good thing. But you don’t need to take my word for it. One barrel of Metaxa Angels’ Treasure was released in 2019, producing 3,500 decanters of the spirit. Coming in at an abv of 42.2%, it’s available for £160 a bottle online which, in the world of spirits, feels like a price that doesn’t match the richness of the story. A further barrel of Angels’ Treasure will be bottled and released in 2024. The bottling is described as “unique” and in the sense that no other spirit has been created under exactly the same conditions, it is. But the Angel’s Treasure phenomenon can’t be unique to this little corner of Attica.

Pulling force

To understand the impact of humidity, our next stop is the tropical climate of the Seychelles and the lush location of La Plaine St. André where Takamaka rum is made and aged. “Our cellar humidity is around 80-90% which acts as an external pulling force, absorbing more of the hydrophilic (water-loving) compounds (ethanol) and leaves behind the hydrophobic (water-phobic) compounds,” says Steven Rioux, cellar master at Takamaka. “In a high humidity environment like ours it is typical to observe alcohol by volume decrease over time due to this cycle. As an example, we can observe a loss of up to 0.8% abv in a year, combined with a physical volume loss of 5:7%.” Indeed, this cycle of evaporation, with the alcohol reducing at a faster pace, is, to some, preferred.

“The liquid that is lost to evaporation is always replaced by oxygen, which then triggers other chemical reactions to help with esterification, among others,” says Rioux. “The drop in abv allows for the liquid to extract additional aromas from the oak that otherwise would not come to be extracted at a higher abv.”

Even in a dry cellar, the concentrating effect caused by increased rates of water loss might not always be the aim. Which takes us to my next stop: Norway and a visit to Anora aquavit – producer of Linie, OP Anderson and Larsen – near Oslo. Here the warehouse is dry at around 55% humidity and a temperature of 15°C. Morten Paulsen, senior product developer at Anora Group, confirms the occurrence of increased water loss and abv creep. “Over a five-year period the abv increases around 2-3%,” he says.

Anora’s aquavits are typically aged for between six months and five years, so the impact is less pronounced. “For liquids with a longer maturation time (our oldest commercial aquavit, Gilde Non Plus Ultra, is matured 12 years),” says Paulsen, “we need to re-rack the aquavit from one cask to another and adjust the abv with water typically every five years in order to avoid over-extraction of certain oak components such as tannins, which are extracted from the wood at higher abvs.”

So, if the Angel’s Treasure effect isn’t always the objective, in some cases, such as at Scotland’s rum company Dark Matter Distillers, it was a complete – and happy – accident. “We filled a virgin oak cask with our rum at 63.5% and then left it in our own little warehouse – six years later and it’s gone up to 66.3%,” says co-founder Jim Ewan. A limited-edition series called The Dark Matter Physicist Series was released, the nine bottles selling at auction for £40k. When the rum is older, Ewan says more releases could follow, although isn’t convinced the abv will rise further.

There are likely many more examples of Angel’s Treasure out there. For some, it is an anomaly to be blended out or water-corrected. Harnessed and marketed, as Metaxa has, it’s most certainly something to treasure.