Rum Aging Science Vol. 3: American Oak vs. French Oak Part 4

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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 agains those obtained from the rums in volumes 1 and 2.

Rum aged in a new, French oak barrel, after 3 months

Our rum has now spent three months inside its barrel at Rum Central’s aging cellar.  March was a month of extremes: colder than normal and also warmer than normal.  Some days in March saw extreme temperature fluctuations, with night-time temperatures in the 30s and afternoon temperatures in the 80s.  These deltas are great for wood extraction but are awful for planning your wardrobe!

                                    Organoleptic Changes

The rum’s aroma is still very “raw” (it has intense notes of fresh alcohol).  The increased level of tannins present in French oak comes across as having a spicy character, with aromas similar to cinnamon and clove.  The taste is definitely harsh, as the tannins have not had the opportunity 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 were aged in American Oak barrels. Notice the increased acidification (lower pH) in the new barrels versus the used one. 

And these are the changes in ABV % readings (as of first day of each month), also compared to the American Oak barrels:

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