Rum Aging Science - American Oak: New vs. Used Part V

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                        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.

                     April’s Weather

While the average temperature for the month of April may seem in line with historical records, a couple of weeks were considerably warmer and a couple were considerably colder.  The daily deltas (differences between highest and lowest temperatures) were quite significant too, as depicted by the graph below.

At the end of the month we saw a much-needed increase in precipitation, with a corresponding rise in relative humidity.

Heat’s Magic

The arrival of higher temperatures marks the beginning of higher extraction rates from the barrels.  Not only does solubility increase, but the volume of the rum increases inside the barrel, causing higher pressure which, in turn, forces the rum deeper into the staves.  The increased volume also results in higher evaporation losses and leakage.  The photograph above shows rum “bubbling” out of the barrel, through minuscule gaps between the silicone bung and the oak.

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:

And these are the changes in ABV % readings, also compared to the ex-Bourbon barrel:

Color: The monthly change in color continues to be significant, even to the naked eye.  The last sample retrieved from the barrel has deeper reddish-copper hues, that make it more appealing.

Taste: The rum’s flavor has a more pronounced oak dimension, as suggested by the color.  The majority of the extracted tannins are still “harsh,” meaning un-oxidized, but are nonetheless helping to make the rum more interesting and complex.  The reduced pH (increased acidity) is also starting to come across, with enhanced fruity notes starting to develop.

Join us again next month, as we continue to explore the fascinating world of rum aging!