Maturation Chemistry: The Wood-Spirit Interaction
Extraction, Oxidation, and Congener Transformation
Many Alcoholic Spirits, such as whiskey, brandy, and aged rum, undergo maturation in oak barrels. This document details the three primary chemical mechanisms of aging:
Extractive: The ethanol acts as a solvent, pulling lignin, tannins, and vanillin from the wood staves.
Subtractive: The charred interior of the barrel acts as an activated carbon filter, absorbing harsh sulfur compounds (like dimethyl trisulfide).
Interactive: Micro-oxygenation occurs through the porous wood, facilitating the oxidation of alcohols into aldehydes and then into esters, which provide fruity and floral notes.
The document also quantifies the "Angel's Share"—the $2$% to $4$% annual loss of volume through evaporation, which concentrates the remaining spirit.
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