Wooden Tannins
Tannins and their Contributions to Aged Rum
One of the flagship characteristics of traditionally-aged rum is the presence of oak tannins and their effect on the gustatory experience. Tannins are astringent components that derive their name from their ability to tan leather.
Oak tannins are hydrolyzable (or Pyrogallols) because they break down to smaller components (such as Ellagic Acid) in the presence of water. They are different from grape tannins (found in dark wines) which do not break down and for this reason are referred to as being condensed (or Catechols). Of the two types of tannins, the former are generally less astringent than the latter.
Oak tannins exist in trees as a form of self defense: their bitterness and astringency act as a defense against predators. They are formed when glucose is combined with ellagic or gallic acids.
Which oak variety has the strongest concentration of tannins? The answer is French Oak, with up to 10% of its weight being comprised by tannins, as opposed to American Oak, which has between 0.2% and 8% tannins by weight. Keep in mind, however, that tannins are destroyed by heat and are hydolyzable, so if you want the strongest concentration of tannins possible, you should use a barrel made of French Oak, un-toasted, with staves that have not been cured for a prolonged period of time (more on wood curing in Lesson 6).
Flavor contributions of tannins:
• Mouthfeel: oak tannins have an impact on the organoleptic qualities of rum, adding to its balance, structure and roundness.
• Color Fixation and Stability: wine research studies have demonstrated that tannins play an important role in stabilizing color in wines, further research is needed to confirm that this benefit extends to distilled beverages, but empirical practice seems to suggest it does.
• Antioxidation: tannins are able to reduce or eliminate the oxidation of other chemical compounds by bonding to the oxygen molecules present in the solution.