Rum Aging Science American Oak Barrels
Rum Aging Science - Rum Central
Introduction
In our first 12-part series, published from January through December 2020, we explored the transformation of rum, while aging in an ex-whiskey barrel. We selected an ex-whiskey barrel for that initial series because the majority of the rum aged around the world employs this type of barrel. The reason for the popularity of this choice is the fact that whiskey producers are required to age their spirit in new oak barrels and, once emptied, they cannot re-fill the barrels, thus creating a surplus of barrels that many other spirits are happy to use in their aging programs.
During the course of the first series, we received a considerable number of inquiries, asking how the results presented would differ if we were using new barrels. This new 12-part series is devoted specifically to address this topic: we will be conducting the same type of research as we did previously, examining the month-to-month changes to the rum while it ages in a new barrel, but also presenting side-by-side comparisons to the corresponding results from the used barrels.
There are many different levels of heat treatment that can be applied to a new barrel. This series focuses exclusively on American Oak with a Char #1 (staves and heads), from Independent Stave Company/Missouri Cooperage. The future series will explore different Char and toast level combinations, as well as, barrels constructed using French Oak.
February’s Weather
Texas experienced one of the coldest February’s in recent memory, with millions of people suffering through it without electricity and water. A picture is worth a thousand words, and there is no easier way to explain how cold it was INSIDE the aging cellar than through this simple chart:
February temperature
As you can see, the temperature dropped significantly, as ice and snow accumulated on the roof and against the walls of the building.
As the snow and ice started to thaw, relative humidity inside the warehouse soared too, as recorded on the following chart:
February humidity
Fortunately, as we write these lines, the weather is returning to “normal” by Texas’ standards, so pretty soon we’ll be having barbeques and mojitos by the pool!
Low Temperature and Aging:
The solubility of many solids increases with temperature. The increase in kinetic energy that comes with higher temperatures allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions. What this means in the world of rum aging, is that the hotter the rum inside the barrel, the higher the extraction rate from the barrel will be. On the other hand, the colder the rum, the less barrel extraction will take place.
Given the extremely low temperature experienced by the rum during February, we expect a reduced quantity of tannins and lignin extracted from the barrels, compared to what the quantity would have been in a warmer month.
Color transformation of rum
Above: the color transformation of the rum in a new charred barrel. one month in a new barrel extracted more wood and tannins than 12 months in a used one. Two months later, the color has rich golden and red hues.
These are the pH readings, as recorded on the 1st day of each month, compared to the rum from the previous series, which was aged in an ex-Bourbon barrel:
ph level in ex bourbon barrels
And these are the changes in ABV % readings, also compared to the ex-Bourbon barrel:
ABV% in ex-bourbon barrels
Color: Even though a significant part of the month had temperatures near freezing, the darkening of the color indicates a noticeable increase in wood extractives.
Taste: Looks can be deceiving and, while the color is now suggesting deep, complex flavors, the reality is that the taste is very one-dimensional and astringent. The wood extractives need additional time, much of it, in order to oxidize and soften.
Join us again next month, as we continue to explore the fascinating world of rum aging!