As if understanding whiskey could get any more complex. You throw in the term “barrel-proof” and you’ve got a whole new set of questions. Whiskey is a spirit that is relatively simple, in terms of ingredients, but beyond the basic way that it’s made, that's where things can get complicated. To understand what barrel-proof whiskey is and why you should try it, first you have to understand the role of the barrel and the aging process.

What is barrel-proof whiskey?

Barrel-proof whiskey is whiskey that has had no additional water added before bottling. The term “barrel proof” was officially defined in 1979 by the Federal Bureau of Alcohol, Tobacco and Firearms as a way to establish guidelines for the use of the terms original proof, original barrel proof, entry proof and barrel proof on distilled spirits labels. The bureau defines original proof, original barrel proof and entry proof on a label as indicating the same thing: “that the proof of the spirits entered into the barrel and the proof of the bottled spirits are the same.” In layman's terms, barrel-proof means it’s an uncut, minimally filtered liquid. 

How barrel-proof affects the flavor 

Proof, which is the measure of alcohol content equal to twice the percentage of alcohol by volume (For example, a 100 proof spirit is 50 percent alcohol), changes during aging. In Scotland, proof typically stays the same or goes down because of the consistently cool climate. In Kentucky and Tennessee proof almost always goes up because the weather is warmer and only new barrels are used.

During the process of aging whiskey and due to the porous nature of wood barrels, a small percentage (roughly 2 percent) of every barreled whiskey batch is lost. Traditionally, it was believed that this whiskey evaporated up to the heavens and, thus, it was coined the “Angel’s Share.” In hot, dry climates, the whiskey’s strength increases over time because the barrel loses water at a faster rate than alcohol. The environment of the warehouse and a barrel’s specific location can also affect the whiskey’s final ABV (alcohol by volume). According to the Alcohol and Tobacco Tax and Trade Bureau’s rule, a whiskey that is bottled at no more than two degrees of proof lower than when it came out of the barrel may be labeled as “barrel proof.” The “two degrees” rule gives distillers leeway if proof drops slightly prior to bottling. But the intention is for the proof in the bottle to match that of the barrel. 

Why should you try barrel-proof whiskey

Whiskey connoisseurs demand this type of whiskey as it delivers big, bold aromas and flavors which for many whiskey drinkers, is as good as it gets. There are other reasons barrel-proof whiskey delivers an intense experience. Master taster, Jackie Zykan explains that it depends on the concentration of the ethanol in the glass, which allows your nose and palates to detect different aromas and flavors. “Different aromatic compounds will leave the solution, and be volatile and floating about in the air, right above your glass, at different proof points,” she says. “If you concentrate the liquid in the barrel, then yes, it’s going to have flavor. But it’s not necessarily just [due to] higher alcohol content that it has more flavor, it’s the fact that you’ve condensed the liquid volume.” 

She also says the humid environment plays a key role in maturation. “Water loves balance; osmosis is always leading the charge.” A porous barrel resting in a dry climate will cause the water molecules to balance. “They’re going to shoot out into the environment,” she says, “leaving a greater concentration of ethanol in the barrel, boosting the whiskey’s proof.” And at higher proof, flavors just get more concentrated. Be forewarned that barrel-proof spirits typically carry a higher price for premium whiskey. But you can make the case that since you’re not paying for added water, the increase in cost is an equal trade off for higher value or quality.