It was a blindingly bright summer day in Islay—a remote, windswept Scottish island synonymous with smoky scotch—when American writer Aaron Goldfarb learned about cold fingering. What sounded like hot high school gossip was actually a solution to a problem Goldfarb had had since he started writing his book, Hacking Whiskey, a collection of DIY ways to take your whiskey to the next level at home.
Goldfarb was tired of bourbon distilleries releasing products at 80 proof, the lowest alcohol content a spirit can legally have to still be called bourbon (most bourbon in the barrel is 110+ proof). Bottling a lower-proof bourbon means a distillery can sell more inventory per barrel, and the lighter flavor can be more palatable for the general public. “I was constantly trying these 80-proof bourbons that smelled great, but when you sipped them they were like bourbon-flavored water,” Goldfarb says. “I could tell a great flavor was hidden underneath, it had just been ruined by being watered down.”
He embarked on a mission to find a way to raise the proof of commercial whiskey, not sure if such a way even existed. “What I wanted to see if I could remove the water from an 80-proof bourbon and get it closer to its natural strength, mouthfeel, and taste,” says Goldfarb.
Goldfarb went to Islay to see the more than 200-year-old Ardbeg distillery during his book research and writing. He toured the seaside distillery with its highly-acclaimed director of whisky creation, distilling, and whisky stocks, Dr. Bill Lumsden, a guy who also holds a PhD in biochemistry. “One of the brightest minds in whiskey,” Goldfarb notes.
In the distillery’s barrel warehouse, Lumsden mentioned that sometimes a barrel’s contents can fall below the 80-proof legal minimum briefly due to climate, and that there were two ways of rectifying the problem. One was legal: to blend under-proof scotch with a higher proof one. The illegal second way was something called cold fingering.
Goldfarb thought he’d found the answer to his bourbon problem. “Except—he wouldn't tell me what exactly cold fingering was,” Goldfarb says. “He just said the words and walked away to continue giving the tour, leaving me stunned, and still left with so many questions.”
After his Islay visit, Goldfarb would go on to ask more whiskey experts about cold fingering, but no one had heard about the term before. He was confused, thinking maybe Lumsden was fucking with him. Not only was the name ridiculous, but it was coming from a man with an infamous sense of humor.
“Besides being brilliant, [Lumsden] is one of the biggest jokesters in the industry,” says Goldfarb. “He might have loved the idea that some naive American writer was going around asking any distiller he could find: ‘Hey, do you know how to cold finger?’ ‘Do I know how to WHAT?!’”
Back in New York, Goldfarb finally found someone who knew about the unfortunately-named proof-raising process. “It would take the equally brilliant Dave Arnold to finally tell me about cold fingering,” he says.
Goldfarb describes Arnold as “the world’s maddest scientist of alcohol, a chef, a bar owner (formerly of the brilliant Booker & Dax), an inventor, and even an author of the unbelievable Liquid Intelligence.”
Arnold shared that the cold finger is a device (shaped like a finger, hence the name) you can use as a condenser on a rotary evaporator. It can cool alcohol down to −78°C and eliminate its water. The result: a higher-proof liquid.
Costing more than $10,000, a rotary evaporator (or rotovap) is impractical as hell for the everyman. Arnold advised Goldfarb not to waste his time on the cold finger method, and to try a much easier method with a more professional sounding name, cryo-concentration.
Arnold explained that cryo-concentration is when you chill a liquor below its crystallization point, then filter out the frozen crystals before they melt (he uses a French press). For an 80-proof liquor, that crystallization starts at about -23C. To get that cold ass temperature, all you need to do is put your whiskey into a styrofoam cooler with dry ice, and the magic will happen.
The pro tip came at the perfect time.
“This sounds like an apocryphal story, but the same day Dave Arnold told me about cryo-concentration I received one of those big holiday packages in the mail from my father-in-law (you know, fruit and cheese and charcuterie and shit) that was packed on dry ice in a styrofoam cooler,” Goldfarb says. “I had no excuse not to try it.”
The breakthrough was momentous for Goldfarb, although it might not be life changing for the general population.
“I don't see frat boys all of the sudden doing this just to make their alcohol more alcoholic,” Goldfarb says. “But, for geeks, this is a fun experiment to conduct to see if you can make a weaker bourbon have more body and flavor. Although, knock yourself out, frat boys.”
Aaron Goldfarb’s book is available for purchase online here.