Rum Aging Science Vol. 3: American Oak vs. French Oak Part 2

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                                          Introduction

In Volume 1 of Rum Aging Science (published from January through December of 2020), we explored the aging of rum in American Oak, ex-Whiskey barrels.  In Volume 2 (published from January through December of 2021) we explored the aging of rum in new American Oak barrels.  This year’s Volume explores the aging of rum in French Oak barrels.

The Rum: Just as we did in Volumes 1 and 2, this new series starts using a low-congener, column-distilled rum, made from fermented HT (High Test or “miel virgen”) molasses.  We use low-congener rum so that we can focus more on detecting the wood extractables and their impact on the rum’s profile.

The Barrel: For this series we selected a barrel made by Independent Stave Company (https://www.independentstavecompany.com), with toasted staves and Char #1 heads.

The Wood Extractives: The compositions of both American Oak and French Oak have a lot of things in common: they are, after all, both oaks.  But the proportions of the components that are extractable by alcohol differ between the two types of oak.  These extractives include:

  • Cellulose - is the most abundant natural polymer on earth.  It consists of linear chains of glucose units and remains relatively intact even after wood curing and toasting.
  • Hemicellulose - also known as a “wood sugar” is a two-dimensional polymer comprised of many simple sugars, including: Glucose, Xylose, Mannose, Arabinose, Galactose and Rhamnose.
  • Lignin - despite the fact that it is also one of the most abundant nature-produced materials on earth, lignin remains one of the least understood.  Oak ligning consists of two building blocks: guaiacyl and syringyl.  The former is responsible for producing coniferaldehyde, vanillin and vanillic acid, which -especially the vanillin- are easily recognized in cask-condition spirits.
  • Oak tannins - these plant polyphenols derive their name from the Latin word tannum, which means “crushed oak bark,” since in early times oak trees served as a major source of tannin for the leather-tannin industry.  Tannins improve aged rum’s character by increasing the perception of balance, complexity and roundness.

Scope of Study

Each month we will evaluate a sample of the rum collected from the barrel and will report its pH, ABV and color. We’ll compare these results against those obtained from the rums in Volumes 1 and 2.

Well, our rum has spent its first month inside the barrel at Rum Central’s aging cellar.  It was one of the coldest months of the year, but the rum nonetheless managed to interact with the barrel to extract tannins, ligning, cellulos, etc.  If we had filled the barrel in June, the first 30 days would have resulted in higher extraction levels due to the increased heat, but we’ll get to that later.  All of the previous Volumes of Rum Aging Science have been based on 12 months (Jan-Dec) and this one will not be an exemption.

                                        Organoleptic Changes

The aroma is very raw/fresh, meaning harsh and superficial.  The increased level of tannins present in French oak come across as having a spicy character, similar to cinnamon and clove.  The taste is definitely harsh, as the tannins have not had a chance to oxidize and there has been very little time for esterification.

Physical Changes

These are the pH readings, as recorded on the 1st day of each month, compared to the rums from the previous Volumes, which was aged in an ex-Bourbon barrel.  Notice how quickly the pH goes from neutral to acid:

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

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