In Part 4 of our “What is Bourbon” series, dig into the final requirement for a spirit to be considered bourbon – the aging process – and how that can impact not only how a bourbon tastes, but also how it is labeled.

First, as a bit of a refresher, recall that the legal definition of bourbon whisky, according to the TTB, is:

Whisky produced in the U.S. at not exceeding 80% alcohol by volume (160 proof) from a fermented mash of not less than 51 percent corn and stored at not more than 62.5% alcohol by volume (125 proof) in charred new oak containers.

 

For those new to whisk(e)y or unfamiliar with the process, it’s often a surprise that it all comes off the still clear. It’s only through the aging process in a barrel that the spirit gains it’s familiar caramel or amber colors. The barrel also contributes many of the flavors and aromas we’ve come to expect from our favorite whiskies.

This portion of the definition really covers two details: the storage in a barrel and a limit on the alcohol by volume during said storage.

Before we jump into both details, it’s fair to ask: why is whisky barrel aged at all? The answer is a practical one. Back when whisky was first distilled, the best way to store and ship the finished product was in wooden casks. As we touched on in Part 1, Bourbon whisky, in particular, was shipped down the Ohio River to New Orleans in wooden barrels marked for Bourbon Street. Most spirits of the day would have been stored in barrels, but only over time did people realize the benefits of barrel aging.

American Oak must be used in the making of bourbon barrels. Oak has a unique physical and chemical nature that allows it to be manipulated into a barrel, but also has a tight enough grain that it will not leak while still allowing oxygen to move in and out of the spirit.

Beyond these physical characteristics, though, the oak offers three effects on an aging spirit:

1. It adds to the taste and aroma of the spirit, such as vanillins, lactones, and wood sugars
2. It acts as a filter, removing undesirable elements from the spirit such as sulfur compounds
3. It converts unpleasant compounds, such as acetic acid, into more organoleptically desirable elements, like fruity esters

 

Essentially, the chemical breakdown of the wood sugars contributes flavors that are desirable, while the wood and char combine to contribute spice and toast characteristics.

The second half of this section relates to the proof/abv during the aging process. The Standards of Identity from the TTB requires that the spirit enter the barrel at no higher than 125 proof or 62.5% alcohol by volume. One reason for this is tradition. Early distillery equipment likely didn’t distill the spirit to a very high proof.

The second reason to maintain an upper limit on proof is to keep the level of extraction from getting too out of hand. If you’ve tasted a lot of whiskies, chances are that you’ve run across a whisky that was “over-extracted”. By this, we mean too oaky and on the verge of tasting like a stale cigarette. The higher the proof of the spirit in the barrel, the more quickly it will pull flavors from the barrel and the less time it will have to mellow out and interact with the char, providing the filtering effect.

The length of time the spirits rests in a barrel impacts the final characteristics, too. In general, the longer a spirits rests, the more mellow it will become. Nearly all whisky that is aged less than two years requires a statement of age on the label. This gets into some of the different indicators you can look for on a bottle of bourbon. For example:

Straight Bourbon – must be aged a minimum of two years.

Bottled in Bond Bourbon – must be aged a minimum of four years, distilled in a single season, and bottled at 100 proof.

Finally, the size of the barrel has an impact on the aging process, flavors, aromas and finish of a whisky as well. The smaller the barrel, the greater the surface area-to-volume ratio there is between the wood barrel and the resting whisky. In turn, the smaller the barrel, the faster the aging process and the more flavor will be pulled from the wood. Many start-up distilleries will use 5, 10, or 15 gallon barrels to age their first-release whiskies more quickly, versus opting for a traditional 53 gallon barrel. While this does speed up the process, a distiller also runs the risk of overextraction of tannins, oak, and undesirable flavors, without allowing time for mellowing.

For the Wayfarer’s Whisky Series, our experimental line-up of whiskies, we used 30 gallon barrels with toasted staves and a #3 char from the Barrel Mill in Minnesota. Through careful monitoring and precise heads and tails cuts in the distillation process, our team is able to age our Wheat Whisky, Rye Whisky, Malt Whisky and Bourbon for 8 to 24 months and get a good idea of how the whisky will age over time in larger barrels. Then, once we settled on our mash bills (grain recipes), we started scaling all of our production up to large barrel whisky that we’ll age for 2-6+ years.