Rum Aging Science American Oak Barrels
Rum Aging Science Oak barrels
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. Future series will explore different Char and toast level combinations, as well as, barrels constructed using French Oak.
July’s Weather
July and August are -historically- the two hottest months of the year in Central Texas, with average high temperatures usually hovering above 100F. This July, however, was a bit cooler than normal, with above-average precipitations during the first half of the month.
The daily temperature deltas (differences between highest and lowest temperatures) were quite significant too, as depicted by the graph below.
July Temperature
The humidity deltas closely followed their temperature counterparts (although inversely), showing the high relative humidity during the night and its decrease caused by the intense heat from the sun.
Humidity for July
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 readings in ex-bourbon barrel for July
As you can see, despite starting with the same pH, the rum in the new barrel has consistently developed more acidity than the one in the used (ex-Bourbon) barrel.
And these are the changes in ABV % readings (as of first day of each month), also compared to the ex-Bourbon barrel:
ABV reading in ex-bourbon barrel for July
Color
The monthly increase in color intensity continues to be significant, even to the naked eye. This color is a good indication of the amount of wood extractable material present in the rum. Since higher temperatures help dissolve these materials more than colder temperatures, we expect the extraction rate during the summer to be at its highest. Keep in mind, however, that the more we extract from the barrels now, the less there will be left for us to extract in the future, which explains why the ex-bourbon barrel imparted a much lower color level than the new barrel.
color transformation of the rum in a new charred barrel for July
Aroma and Taste
The rum now has a very well-defined fruitiness that comes across first on the nose and then on the palate. The fruity notes are reminiscent of young Armagnac/Brandy and are the result of aldehydes and esters forming inside the barrel. The oak dimension of the rum continues to build up, becoming fuller, softer and more complex with every passing month, but still harsh from fresh tannins that have not been oxidized (the extraction rate still exceeds the oxidation/reduction rate).
Join us again next month, as we continue to explore the fascinating world of rum aging!