Rum Aging Science Vol. 3
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.
French Oak barrel made by Independent Stave Company
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.
How French is French Oak?
One of the most common misconceptions about “French Oak” barrels is that they are made using wood from oak trees that grew in France or in French territories. The truth, however, is that it has nothing to do with where the tree grew, instead it is all about the particular species of oak tree.
By the same token, “American Oak” barrels are not defined as barrels made from oak trees that grew in the USA or in the American Continent, but rather refer to the species of oak tree used in their manufacture.
Barrels made from French oak (Quercus pedunculata) have always been more expensive than their American oak (Quercus alba) counterparts, leading (or misleading) people into thinking that the former are better. The reason for the price difference is basic economics:
An average American oak tree will yield twice the number of barrels as a French oak tree of identical size. Why?
As a tree reaches maturity, it undergoes a process known as duraminisation, when heartwood is formed. During this transformation, “parenchymal cells located near the large sap-conductive vessels excrete a membranous protuberance, known as a tylose, which partially blocks the vessels1.” It is this obstruction which gives American oak its water-tight characteristic, regardless of how the wood is milled, whereas the absence of tyloses in French oak result in the need to mill the wood in a more restrictive way to preserve its impermeability.
Both woods are great for aging spirits, but each type has advantages and disadvantages based on their characteristics:
French Oak has 10 times (or more) higher level of tannins than American Oak. Always select this oak type for your barrels when you seek to obtain a higher tannic concentration.
American Oak has a higher concentration of Oak Lactones than its French counterpart. Always select this oak type for your barrels when you seek to obtain traditional Whiskey/Bourbon notes, like toasted coconut, almond, etc.
Join us again next month as we explore the transformation of the rum during its first month inside the barrel.
1 Dr. J. A. Hueso, Tonelería Victoria