Lesson 4 of Rum University
Lesson 4: Chemical Properties of OakThis is lesson 4 of 12 of "The History and Science of the Barrel" available through The Rum University's website, www.RumUniversity.comLesson 4: Chemical Properties of Oak
Oak barrels and the source of their flavors
In addition to the physical properties of oak, which we described in Lesson 3, the major building blocks of oak wood also contribute greatly to the flavor of the rum aged in its barrels. The table in photo illustrates these components along with the flavors and aromas each influences.
The presence of these components (cellulose, hemicellulose, ligning, tannins and char) by themselves does not guarantee the rum will acquire the taste or aroma desired. One needs to look at the intensity/concentration of each one in connection with the wood curing process employed (Lesson 6) and the toasting or charring method selected for each barrel (Lesson 8).
The graph (see photo above) shows us the average makeup of oak in term of these components.
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.
Our special thanks to Independent Stave Company for their support in our research of oak.