Chemists and bioscientists from the University of Glasgow developed the test, which harnesses a unique property of cask-aged whisky to measure its maturity.

Each variety of whisky gains some of its color flavor profile from being stored in wooden casks while it matures over a period of months or years. The flavor of the final product is created by a complex mix of factors known as “congeners”—chemicals left in the spirit after it is distilled and other chemicals absorbed from the wood casks, which react with oxygen over time.

The unpredictable interactions of congeners, along with other factors like the size and shape of the cask and the number of times it has been used before, mean that each cask matures in its own way, and in its own time.

To ensure the consistency of their products, distillers employ highly experienced master blenders. They regularly sample the casks to check the whisky’s readiness for blending, bottling and sale as either a single malt or a mixed blend—a laborious and expensive task.

The researchers set out to develop a test which could do some of the work of the master blenders by using chemical reactions to determine the maturity or “age” of whisky samples.

They built their test on a reaction which occurs when samples of whisky are mixed with a solution containing small quantities of a special type of gold. A chemical reaction in the whisky causes distinctively-colored gold nanoparticles to form in the sample over a short period of time at room temperature.

The researchers mixed the gold solution with samples from 15 different whiskies distilled in Scotland, Japan and the U.S. They also tested multiple samples taken at regular intervals from a single cask over a period of six years, which were supplied by the Scotch Whisky Research Institute.

By measuring a property of each sample known as its localized surface plasmon resonance, they found that the unique chemical composition of the whiskies resulted in the creation of gold nanoparticles with distinctly different shapes, sizes and colors in each sample.

They also discovered that the speed of the production of the nanoparticles was connected with its maturity—the faster the nanoparticles formed, the more mature the whisky was.

The results suggest that the process could be used to develop a quick, reliable test for distillers to measure the maturity of their whiskies, reducing the need for master blenders to be involved in every step of the process.

Dr. Will Peveler, of the University of Glasgow’s School of Chemistry, is the paper’s lead author. Dr. Peveler said, “Age is more than just a number when it comes to whisky—the complex chemical reactions which occur in each cask make it impossible to estimate whisky’s maturity of flavor simply based on how long it’s been aging.

“For as long as there’s been a whisky industry, distillers have been trying to find better ways to measure the maturity of individual casks to help them understand when they will be ready to use in a single malt or a mixed blend.

“What we’ve been able to do for the first time is show that the aging-related chemistry of the whisky controls the formation of gold nanoparticles. That has allowed us to develop a unique ‘fingerprint’ not just for types of whisky we tested but also for how whiskies mature over time.

Co-author Dr. Jenny Gracie, also of the School of Chemistry, added, “Currently, there are a number of other tests available to measure whisky maturity, which use specialist processes like chromatography and mass spectrometry. However, they are rarely available on the warehouse floor, and if samples have to be sent offsite for analysis, this slows everything down.

“We hope that in the future we can develop this initial finding into a quick, easy and portable kit that distillers can use to measure the maturity of their whiskies without having to send samples for time-consuming tests with specialist equipment.”

The team’s paper, titled “Growth of Plasmonic Nanoparticles for Aging Cask-Matured Whisky,” is published in ACS Applied Nano Materials.

Sukhinder Singh and his brother Rajbir were pioneers of online retail in the sector, starting The Whisky Exchange in 1999. The pair sold the company to Chivas Regal brand owner Pernod Ricard in 2021 and are now expanding into production — in addition to retailing — through their Elixir Distillers business. The brothers are building a distillery on Islay, the Hebridean island already famous for its whisky, and buying the Speyside Tormore brand from the French company. “More and more people are falling in love with whisky,” said Sukhinder, but it will be years before the increased capacity catches up with demand, he added, because “you can’t just turn the tap on”. Artisanal Spirits Company is the listed Scotch producer that owns the more than 35,000-member Scotch Malt Whisky Society. Managing director David Ridley said the high end of the market could be worth as much as $4.3bn.

In July, the company reported a “standout” 50 per cent rise in sales in China at its interim results. “The desirability of what we have to offer surmounts the current situation in terms of the economy,” Ridley said. Graeme Littlejohn, strategy and communications director at the SWA, said the long-term nature of the industry meant it was able to defy short-term economic volatility, noting that at the height of the financial crisis in 2008-11, exports rose by 40 per cent. While it was “not immune to the global situation, the long-term vision means some of the bumps in the road are lessened”.

The spirit’s tasting notes on its aroma say: “Brazil nuts in toffee fill the nose, followed by linseed oil, a suggestion of flowering blackcurrants, sweet, aromatic peat smoke and a hint of tobacco”.

Ardbeg chief executive Thomas Moradpour said: “This sale is a source of pride for everyone in the Ardbeg community who has made our journey possible.

“Just 25 years ago, Ardbeg was on the brink of extinction, but today it is one of the most sought-after whiskies in the world.”

Andrew Shirley, editor of the Knight Frank Wealth Report, said that the cask sale had “set a very interesting new benchmark”.

Whisky expert Charles MacLean added: “This truly unique whisky is a remarkable piece of liquid history – an evocative taste of what Ardbeg was like when it malted its own barley.”