Small oak barrels can be a great way to quickly age spirits, especially whiskey, rum, tequila and bourbon. Because they expose a greater surface area per volume of liquid to the wood, they can more quickly diffuse the woody flavor of oak – a product of lignin, vanillin, and small traces of tannins that are extracted from the cell walls of the wood – throughout the drink inside, resulting in a finely aged spirit, wine, or even beer in a fraction of the time that would be spent in an industry-standard 53 gallon barrel. The general cause of this is that the volume of small oak barrels increases by a power of three relative to dimensions, while surface area increases by a power of two.
How much faster is the aging process in small oak barrels?
The aging process in small oak barrels is dependent on several factors, including what exactly is being aged. The general rule is that the aging process can be sped up from about two to six times, depending on the size of the miniature barrel. As a result, aging for a year in small oak barrels could impart the same flavor as aging for two to six in an industry-standard barrel. While spirits may be aged much faster, the disadvantage is that they cannot be aged in large quantities.
There are many other factors that affect the aging process in small oak barrels, aside from those already mentioned. The type of oak is one of them; American white oak is considerably more dense than European oak, for example. The prior occupant of the small oak barrels may also change the characteristics of the spirit, whether that be a previous spirit or the fact that the barrel is unused. How charred the small oak barrels are on the inside can also affect the characteristics of a spirit, as the charring acts as a charcoal filter. The conditions in which the barrel is stored can affect the evaporation of water or alcohol, especially humidity. Temperature also affects the aging process, where warmer temperatures cause it to accelerate, and lower temperatures cause it to slow.
The chemistry of an aging spirit is extremely complex, yet straightforward, and does not take place any differently inside of small oak barrels. Aging is a purely chemical process, and it takes place due to the reactions between the alcohol of the spirit, the congeners (general substances produced during fermentation, such as esters, acetone, and other chemicals), oxidation, and the leeching of chemicals out of the wooden barrel into the substance housed within. These are affected by the alcohol content of the spirit, the level of charring in the oak barrel, the humidity and the temperature in the aging area, the size of the barrel, and the length of time that aging takes place.
The alcohol content of the spirit mainly affects how the chemicals of the barrel wood leech into the drink. This includes the level of lignins and their derivatives, vanillins , and tannins. It also affects the proportion of congeners formed during fermentation, and how many remain in the drink throughout the aging process.
A higher alcohol content – for example, 80% – extracts more of the desirable compounds and color from the wood of small oak barrels. However, it also extracts tannins, which impart a harsh, bitter astringency to the flavor. Additionally, a higher content of alcohol also means that more water must be added to dilute the substance down to its bottling strength once it has been aged, which also results in a diluted, watery flavor. As such, it would seem that the optimal cask strength is about 55% to 65% ABV, in order to achieve a balance of color and barrel extraction versus tannin production, without having to over-dilute the spirit at bottling time. Unfortunately, the lower alcohol content results in a longer, slower aging process, as the rate of chemical changes taking place and barrel extraction are reduced. This is especially important in new small oak barrels; previously used barrels may be used for stronger spirits, because a portion of the harsh tannins have been leeched out of the wood by the previous batch.
Another advantage to aging in small oak barrels at 55% to 65% is that barrels were found to have increased porosity at that level. This allows more water to escape, while retaining more of the alcohol and other compounds in the aged spirit. This actually results in the alcohol content increasing slightly while in the barrel.
Finally, temperature and humidity can also vastly affect the aging process, especially in small oak barrels. Oxidation is accelerated in higher temperatures, and acids, esters, tannins, furfural, and aromatic compounds are increased as a result. Tropical temperatures in areas where temperature varies between night and day are ideal for faster aging; the aging process may stop altogether during winter in more temperate climates. Slight movement of the barrels also helps to age the liquid within, which is yet another advantage of small oak barrels.
Bottom line – Small oak barrels age quicker. Since you are not aging your whiskey, rum, tequila, bourbon or whatever for the entire country and probably just for your personal use then you can consequently use your oak barrel at home to take your bottom shelf liquor and move it up a shelf or two in just a month or two. Enjoy your small oak barrel at home today.