Why Smaller Barrels Age Faster

Why do smaller barrels age faster?

If a different sized barrel is used then the dynamics change, and values like length of time in the barrel, the rate at which lignin and vanillins are extracted, etc are completely different. The reason for this is volume increases by a power of 3 relative to the dimensions, while surface area only increases by a power of 2 relative to the dimensions. That is to say, the amount of surface area of wood per gallon of spirit is greater in a smaller barrel and less in a bigger barrel.

How much faster do smaller barrels age spirits in the barrel?

I'm glad you asked. Our smallest barrel will age 6.31 times faster than a standard 53 gallon whiskey barrel. Our largest barrel will age 2.12 times faster than a standard 53 gallon whiskey barrel.

Is there anything else that will affect the aging process?

The type of oak: American White Oak is more dense than European/Fench Oak.
Prior use of the barrel: Flavor from the previous use can change the characteristics of your spirit.
The level of charring: Charring acts as an activated carbon filter.
The Angels Share: Either water or alcohol will evaporate depending on humidity and temprature.
Humidity level of the room: Higher humidity means alcohol will evaporate and lower humidity means more water will evaporate which will increase the ABV.
Temprature can affect aging too: Warmer tempratures activate the aging process where colder tempratures will cause the aging process to slow or even stop.

The following is a passage from an article written by the American Distilling Institute.

"It’s still a mystery as to how the barrel confers its lubricious effect on the aging spirit. We do know that aging is related to the chemical changes that take place as a result of reactions with the alcohol and congeners in the spirit through oxidation and extraction of chemicals from the oak. Factors affecting this aging process are: percent alcohol of the spirit; the level of charring of the oak; the temperature and humidity in the aging warehouse; the size of the barrel; and of course, the length of time the aging takes place.

Percent Alcohol of the Spirit: The level of lignin fractions, lignin derivatives, vanillins, and tannin extracted from the oak, as well as the amount of congeners formed, are dependent on the alcohol concentration.

While a high-alcohol concentration, such as 80%, extracts more of the beneficial compounds and color, it can also extract more tannin, which imparts too much astringency and harshness to the flavor. Additionally, the higher the alcohol content, the more water that has to be added to dilute it to bottling strength when the aging is finished. This also dilutes the barrel contribution. So, it has been determined that for whiskey aging in new barrels, 55 to 65% abv is the optimum strength to achieve a balance of barrel extraction and color, with lower tannins. It also reduces the dilution of the barrel compounds at bottling time. However, this lower alcohol concentration also results in slower aging as the rate of chemical change and barrel extraction is reduced. Barrels that are used more than once can age stronger spirits since the harsh tannins have been diminished by the previous contents.

At 55 to 65% abv, barrels were found to have a greater porosity for water, with the fusel alcohols, acids, esters, aldehydes, and furfural being retained. Further studies confirmed that these lower strengths result in an increase in alcohol content after aging, whereas a decrease in strength is found when spirits are aged at higher alcohol concentrations.

Temperature and Humidity: The humidity in the warehouse also plays a significant role. High humidity usually results in a decrease in alcohol strength, and dry warehouses usually have the opposite effect. Humidity also affects the character of the final spirit. It has been found that the extraction of vanillin is better at low humidity. Low-humidity aging does generally result in spirits that have a better sensory quality.

The temperatures in the warehouse affect the oxidation reactions that take place in the spirit, and higher temperatures accelerate these reactions. Since these are great contributors to the aging of the spirit, it’s obviously advantageous to age at higher temperatures. Acids and esters increase due partly to the oxidation of the ethanol to acetic acid via acetaldehyde which is then partially converted to ethyl acetate (an ester). Therefore, a consequence of aging is an increase in the concentration of acids, esters, furfural, tannins, and aromatic compounds as a result of oxidation, condensations, and other interactions with the wood.

Tropical temperatures, especially when there are variations between night and day, are ideal for faster aging, and it has been found that aging may not take place during the winter in temperate climates if the warehouse is not heated. Movement of barrels during the aging period will also help, but this is obviously not a practical approach."