Gold Nanoparticles Key to Lab Test for Whiskey Agedness

As a woman of a certain age, I’ve often tried to convince myself that I’ve gotten better as I have gotten older. My intellect and life experiences are vastly greater than when I was 20, as is the balance in my bank account. Certain things arguably get better with age: cheese, wine, denim jeans, cast-iron skillets, and a staple in my household, whiskey.

When it comes to whiskey, older is usually better. A Macallan Fine and Rare bottle sold for $1.9 million at Sotheby’s in October 2019. Six bottles from the same cask, #263, made of European oak and matured for 60 years, hold the Guinness record for “The World’s Most Expensive Spirit.”¹

Until now, knowing when a whiskey has been aged to its peak has been a somewhat subjective, labor-intensive, and expensive process. But a research team from the University of Glasgow in Scotland, in a six-year study, has developed a way to use tiny amounts of gold to determine whether maturing whiskeys are ready to bottle or blend.

The basics of whiskey production

While whiskey comes in several variants, the ingredient list is quite simple: water, grain, and yeast. The most commonly used grains are barley, corn, rye, and wheat. Some whiskeys are regulated. For example, Scotch whiskey must be made with malted barley, and to be called a bourbon, the product must be made from at least 51 percent corn.²

The grain is germinated in water, creating sugars, and then yeast is added to convert the sugars to alcohol. The mixture is then repeatedly distilled until the result contains upwards of 70 percent ethanol, some water, and the unique chemical composition, known as congeners, that stemmed from the process.

The final step is to transfer the distillate to oak barrels, or casks, for aging. These barrels are first dried, heated, and charred to allow the whiskey to absorb the natural sugars and flavors of the wood, introducing the sweetness of vanilla or spicy, smoky notes. The charred layer also helps remove the spirit’s unwanted flavors, like sulfur.

What defines whiskey maturity?

The age or maturity of a whiskey isn’t just defined by how long it has been sitting in a barrel. Agedness is the subjective measure of how much flavor the spirit has taken in. Numerous factors influence the whiskey’s aging process, including the initial composition, the source of the wood, the production of the cask (i.e., size, shape, density, length of charring treatment), the number of times the cask has been used, the fill level, and the temperature and environment in which the barrel is stored.

Some of the most coveted whiskeys are aged in casks for decades, increasing the complex flavor profile and enhancing the deep amber color. But knowing the age of the barrel is not enough to know how the contents have chemically aged. In warmer climates, barrels can release their flavor more quickly. It might only take a whiskey five years to reach a flavor quality equal to another barrel that has been aging for 10 years in a cooler environment.

Each cask matures in its own way. And while older is usually better, it is possible to over-age whiskey, making it taste almost completely like wood and lose the flavor of the original ingredients.

Current tests for whiskey agedness

To ensure the consistency of their product, many whiskey distillers employ master blenders to regularly conduct tasting sessions to gauge agedness. This process can be labor intensive and expensive, as there is not an infinite supply of experts in this field, and the process ultimately relies on one person’s nose and pallet to determine each cask’s maturity.

Gold Nanoparticles Key to Lab Test for Whiskey Agedness

Alternatively, laboratory assays can measure agedness using mass spectrometry and chromatography, but most distillers do not have on-site labs capable of these specialized testing processes. So samples must be sent offsite, which adds to the cost and timeframe to know the results.

New research: Formation of gold nanoparticles decodes agedness

Inspired by the need to make maturity testing easier and more affordable, a group of chemists and bioscientists from the University of Glasgow’s School of Chemistry discovered that adding an aqueous solution of gold (Au3+) to a sample of whiskey caused the formation of gold nanoparticles. These tiny colored nuggets were visible to the naked eye in minutes and at room temperature.

Using samples from 15 types of whiskeys distilled in the US, Japan, and Scotland, and testing samples obtained at regular intervals from single casks over six years from the Scotch Whisky Research Institute, the laboratory team found that older whiskeys formed colored nanoparticles with a more intense shade of blue, whereas unaged, younger spirits were generally towards the redder end of the spectrum and had less intensity. They also discovered that the faster the nanoparticles formed, the more mature the whiskey was, essentially creating a fingerprint for how whiskeys mature over time.

While using gold might not seem like a cost-saving option, the amount of gold ion needed is small and requires only a 50 microliter sample of whiskey. When compared to the value of a single cask, it makes the test worthwhile. However, in an attempt to lessen the cost, the team at the University did try using silver ions. The end result was that a higher quantity was needed to yield similar results and the reaction time was much slower.

Real-life implications for whiskey distillers

The researchers at the University of Glasgow plan to further investigate how gold nanoparticles grow alongside alcohols and sugars in whiskeys to develop an even more comprehensive test for agedness and compare their correlations with master blenders to connect the chemical and sensory definitions of whiskey maturity.

The test could soon develop into a portable, rapid testing kit for distillers to be used on the warehouse floor, without the need for a full in-house laboratory or having to send the samples off-site for time-consuming tests. A portable UV–visible spectrometer for measuring a few samples at once could also be developed based on a smartphone or other similar technology.

Manage samples (yes, even whiskey samples) with a LIMS

No matter if you’re testing cell samples for cancer research or product samples, like whiskey, to ensure quality and consistency, managing your samples and test results with a laboratory information management system (LIMS), like the LabLynx ELab LIMS, is more efficient than paper or spreadsheets.

Get samples entered quickly and accurately; keep tabs on all of your results by producing plotting, graphing, and trending charts for quality control; and create customized reporting with the LabLynx ELab LIMS.

LabLynx works with many companies and independent laboratories in the food and beverage industry and can create a LIMS software solution tailored to your needs that is flexible, scalable, and secure.

Contact [email protected] or visit our website www.lablynx.com for more information or to schedule a demo of the ELab LIMS.