What Gives Whiskey Its Taste? (Part II)

In our last article, we discussed a couple of the primary factors that affect whiskey flavor development.

We discussed two major contributors: location (which lends whiskey climatory variations like temperature, pressure, and microflora) and fermentation (which affects what flavors develop from the grains). Here, we will discuss three more: distillation, maturation, and bottling.

Thank you to Jeremy DeWitt, Distiller for 10th Mountain Whiskey & Spirit Co. for his time in sharing this knowledge with us. They are distilling Colorado Whiskey that not only honors their craft but honors our Veterans through their philanthropic efforts.

Flavor Development in Whiskey – Part II

Distillation:

The type of still, the proof of the distillate collected, when the cuts are made, and the copper content of the still each lends their own contribution to the resulting flavor. Stills with a taller column allow for more separation in the vapor phase, meaning fewer flavor components such as esters and phenols will be able to tag along as the ethanol vapor rises, resulting in a lighter whiskey. Conversely, traditional pot stills with a shorter column allow less separation in the vapor phase, producing new-make whiskey with a heavier flavor. The proof of the distillate has a similar effect in that higher proof spirits coming from the still include fewer congeners contributing to taste. 

Choosing the cut points also contributes to the overall flavor profile of the whiskey. We want to eliminate the more volatile solvents like methanol and acetone that boil off first. Still, a slight overlap between the heads and hearts can provide some compounds that contribute to the complexity of flavor as it develops in the barrel. Similarly, as we look to make the cut from hearts to tails, a slight overlap can benefit the overall flavor of the resulting whiskey.

During distillation, copper reacts on a molecular level to remove sulfides produced during fermentation, improving the taste and allowing more pleasant aromas to present themselves in the finished product. For this reason, stills are traditionally constructed with copper, and some modern stainless steel variations use a copper mesh in the column.

The 10th Mountain Whiskey Difference: We use a 100% copper still, which helps to rid the alcohol vapors of sulfur during distillation, giving the whiskey a smoother palate. The slight overlap of heads and tails that we allow during distillation provides a complex flavor unique to our whiskey.

Maturation:

Perhaps the most critical factor contributing to the flavor of whiskey is the aging process. For American whiskey, we are required to use charred new oak barrels. Although the type of oak isn’t specified, white oak is the preferred choice for American whiskey distilleries because of the combination of chemicals essential to flavor development.

Toasting and charring the oak cask changes the chemical makeup of the wood by breaking down hemicellulose into simple wood sugars and converting lignin to vanillin, giving the whiskey its caramel, toffee, and vanilla flavors. In addition, the carbon produced during charring acts as a filter to remove sulfur and other unpleasant compounds remaining in the spirit after distillation. A darker char will also create cracks in the surface of the wood, giving it more surface area and making it easier for the spirit to penetrate the wood as it ages. Another factor that helps determine the flavors extracted during maturation is the proof of the new-make whiskey when it enters the barrel. Sugar is more soluble in water than ethanol, so a lower barrel entry proof allows the whiskey to extract more of those simple wood sugars in the barrel’s walls. 

As the whiskey ages, temperature fluctuations allow the barrel to “breathe,” meaning the liquid inside the barrel expands and contracts through the pores in the wood. As the barrel breathes, compounds extracted from the wood result in the creation of esters in the aging spirit. The pores in the wood also allow for some evaporation to occur over time, known as The Angel’s Share. When The Angel’s Share leaves the barrel, a small amount of air is pulled back in, allowing oxidation to assist with esterification. Remember that overlap from the heads and tails cuts? These headsy alcohols are converted into fruity flavors; the tails overlap and are converted to rooty, nutty flavors; this is also when the lignins and tannins turn to vanilla flavors.

The 10th Mountain Whiskey Difference: During aging, the alligator char of our barrels allows more surface area for the spirit to come in contact with, allowing for more extraction of sugars early on. As the temperatures fluctuate, more air is pulled into the barrel as it breathes, allowing more oxidation/esterification. Our barrel entry proof also allows the spirit to pull some sugars out of the wood early on without creating an overwhelming sweetness.

Bottling:

When we are ready to harvest barrels for bottling, we need to consider a few more contributing factors. Batching involves sampling and selecting barrels to combine for the desired flavor. Even if you keep everything mentioned above consistent, there will inevitably be some subtle flavor differences from barrel to barrel. Batching, or mingling, is a way to maintain a consistent flavor profile. Another consideration is the proof at which the whiskey is bottled. Cask strength whiskey straight out of the barrel will pack a punch. Bringing down the proof will make it more approachable by dialing back the harshness of alcohol content, allowing the more subtle flavors and aromas to present themselves as the whiskey opens up. The last contribution to flavor is the filtration process. Filtration removes leftover char from the barrel to improve the appearance, but it can be adjusted to highlight certain flavors while eliminating others. Filtration temperature, micron size and material of the filter, and pressure can all be changed to target the desired flavors.

The 10th Mountain Whiskey Difference: Our dry climate pulls more water than alcohol from the barrels resulting in a higher proof spirit after The Angel’s Share is extracted. While this concentrated, high-proof whiskey is full of flavor, we proof it down to allow some lighter flavors and aromas to shine through. We’ve found that 86P for our rye whiskey and 92P for our bourbon give the best results. However, if you ask one of our bartenders, they might have something higher proof for you to sample that you can only get at our two tasting rooms.