Is Barrel Entry Proof Really That Important?

Let me briefly go over some bourbon history for you to better understand how the concept of barrel entry proof came about. In the early 1800s, whiskey wasn’t sold by the bottle. Instead, it was sold straight from the barrel by the distiller. Customers would bring their own containers such as flasks or canteens to store the whiskey that they purchased. The proof of the whiskey varied slightly, depending on how or where these barrels were stored. Barrel entry proof was typically around 100 to 103 proof and sold around 95-105, depending on how the climate affected the barrels. After prohibition, consumers were no longer able to purchase bourbon from the barrel. Taxes and regulations on alcohol put an end to this.

Once the repeal of prohibition took place and American distillers were able to sell their whiskey again, they began to use glass bottles for storage and sales. Barrel entry proof became a more important component to the craft, and the manipulation of whiskey flavor began to vary more and more from distiller to distiller. Now that whiskey wasn’t sold straight from the barrel, distillers were able to fill their barrels with higher proof bourbon and water it down later, if need be. The legal barrel entry proof was later raised from 110 to 125 in 1962… but most distillers do not exceed 110.

How Barrel Entry Proof Affects Supply and Production Costs

When putting whiskey in barrels, the higher the proof is the fewer barrels you will need, because there is usually less product volume, allowing you to save storage space in the distillery. However, depending on the climate inside the storage area, lower proof bourbon can age much faster, depending on heat and humidity. As a result of the quicker aging process, small, start-up distilleries may want to take advantage of lower entry proof as it helps to create cash flow sooner. Either way, the production costs will vary based on what proof the whiskey is when entering the barrels, as well as the number of barrels required to meet your bottle quota. As you decide what proof to barrel at, keep three things in mind:

  1. Quicker aging process means quicker cash flow.
  2. Lower entry proof is typically deemed more palatable to a wider range of consumers.
  3. The older the whiskey, the bigger the price tag.

How Science and Climate Affect the Flavor of Barrel Aged Spirits

Artificial Heat Cycles vs. Natural Heat Cycles

Depending on the climate in which you store your casks, the proof and flavor are going to vary. Climate variations influence your whiskey’s water-to-alcohol concentration, meaning that in the cool, dryer climates, barrel proof doesn’t change too much. In warmer, more humid climates, barrel proof typically increases significantly.

Some states, such as Florida, experience relatively stable climate changes, while states like Kentucky have very hot summers and very cold winters. Craft distillers in these regions with extreme seasonal weather changes may choose to use temperature controlled warehouses, creating artificial heat cycles. This continues maturation during these chilly months so that they release their product on time. As the whiskey is warmed in the barrel, it will seep into the wood and extract color, flavors, and aromas. When cooled, whiskey flows out of the wood with all of those new elements (we’ll go into this further in the section below).

Extraction, Esterification, Transesterification, Oxidation/Evaporation, and Filtration

There are 5 significant chemical processes that occur during barrel aging:

1. Extraction

Extraction is the absorption of wood sugars from the barrel. Oak casks react depending on the alcohol-to-water ratio. Meaning that, with more water in the whiskey, wood sugars such as tannins and vanillins are dissolved faster. A higher proof allows the tannins to come across too strong, causing a harsh wood flavor and odor (something the guys here at StillDragon refer to as a “tooth-picky” finished product). Lower proof typically equates to a smoother finish.

2. Esterification

Esterification is a chemical transformation process that creates the floral and fruity notes in the distillate; by combining alcohol and carboxylic acids, a chemical compound called an ester is formed. The esters are responsible for both the floral and fruity notes, as well as some of the pungent smells. High acidity = more esters. Rum dunder and spent mash that remain in the kettle after the first distillation run are loaded with esters. Some distillers will repitch these remnants back into the kettle to be distilled with the rest of their alcohol. For whiskey, the mixture of spent mash with the first collection of distillate is often referred to as “sour mash”. These repitching techniques are often used because plenty of consumers enjoy the funky depth and diversity within these whiskies or rums.

3. Transesterification

Transesterification is a process in which newly formed esters within the barrel combine with alcohols creating a constantly evolving occurrence of ester formation. This happens at a very slow rate because a strong acid catalyst and/or heat is required to create and transform these chemical compounds at a rapid rate. This process happens more consistently in very hot, humid climates. Transesterification can, again, further the development of desirable flavors in your finished product.

4. Oxidation/Evaporation

During oxidation, ethanol will slowly evaporate. This gives:

  • Headsy alcohol (rubbing alcohol odor) —-> fruity aroma/ flavor
  • Tailsy alcohol (wet dog/ sweaty shoe odor) —> nutty aroma/ flavor
  • Tannins (wood sugars) —> vanilla aroma/ flavors

5. Filtration

Charring your barrels aids in the process of filtration. Fusel oil molecules (tails) are bigger and denser than ethanol molecules. They are caught and trapped in the charcoal layer before your spirit is absorbed into the oak, reducing the amount of tailsy odors and flavors.

Now, I am by no means saying that barrel aging will completely eradicate these flavors and odors, and you’ll be fine if your distillate is super headsy or tailsy. What I am saying is this: many distillers like to curate their own concoctions by mixing heads, hearts, and tails. If these components are tastefully added back into the hearts, it can actually create a far more desirable and diverse aged product.

(Note: If you would like to dive deeper into the chemical process of oak aging and how different factors affect activity, click here to read more. To read more on the process of esterification in regards to brewing / distillation, click here.)

There are so many different factors that play into the way your finished product tastes and feels in your mouth. When it comes to rum, whiskey, brandy, or tequila, barrel entry proof is not always the make or break. The climate and chemical processes that occur during aging can truly transform and/or enhance your spirit. These factors don’t necessarily make your spirit better or worse, they just make it different. Developing a product that you and your customers love is really what it’s all about.

> Interested in making barrel aged spirits? Give us a ring here at the office (561-903-4689) or shoot us an email at for advice.