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

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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.

                                    November’s Weather

November’s daily temperatures were all over the board, with cold mornings and warm afternoons, often times with 20+ degree swings.  The average low temperatures inside the cellar hovered in the high 50s and low 60s.  The daily highs were in the high 60s and low 70s. 

Relative humidity fluctuated quite a bit too, with lows in the 30% range and highs in the 80% range, as shown below.

As we reach the end of this series, the rum shows no sign of slowing down the extraction of tannins from the barrel, getting darker, richer and more complex.  This rum was darker and had more wood-extractives after one month in a new barrel than the rum we aged in an ex-bourbon barrel for a whole year.

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.  Notice the reduction in pH (increase in alkalinity):

The amount of wood extractives and the increased acidification gained in the new barrel show a clear difference when using new barrels over used ones.  Whether this difference is an advantage or not depends on the profile desired for the rum.

And these are the changes in ABV % readings (as of first day of each month), also compared to the ex-Bourbon barrel:

Color: The monthly change in color continues to be measurable through colorimetry and is definitely noticeable to the naked eye.

Aroma: The wet oak, almond and coconut/nutty notes characteristic of American Oak are in full display.  The aroma is enticing and very promising.

Taste: The organoleptic transformation continues, with all notes gaining in intensity after each passing month.  The oxidized tannins are becoming more noticeable, but fresh (un-oxidized tannins) are still present due to their continuous extraction from the staves. continued on next page

Conclusions

As expected, new barrels offer a higher quantity of wood-extractables than their used counterparts.  Think of it in terms of tea bags: the first cup of tea you brew with a new bag always produces a stronger, more flavorful, more aromatic tea than subsequent cups brewed with the same tea bag.

Why, then, would someone opt for used barrels?

There are several reasons, including:

  • Price.  Used barrels are less expensive than new ones.
  • Availability.  Whiskey producers are not allowed to re-use their barrels, which means there is -usually- a constant supply of used barrels.
  • Profile.  Many consumers prefer “milder” or “softer/gentler” oak dimensions in their rums, something that is not achievable when using new barrels.Which barrel you use depends on a combination of these factors, but savvy distillers/blenders know that they will have more flexibility to create new/different products when they employ a combination of these barrels in their aging programs.

Joins us next year as we explore aging rum in French Oak barrels!