What is the primary mechanism by which barrel char level influences the development of vanillin notes in matured spirits?

The primary mechanism by which barrel char level influences the development of vanillin notes in matured spirits revolves around the thermal degradation of lignin within the oak wood. Lignin is a complex polymer that provides structural support to the wood. During the charring process, which involves exposing the interior of the barrel to high heat, lignin is broken down into various aromatic compounds, including vanillin. The char level directly correlates to the extent of lignin degradation. A higher char level means the barrel is exposed to higher temperatures for a longer duration, leading to more significant lignin breakdown and, consequently, a higher concentration of vanillin precursors in the charred layer. These precursors are extracted by the spirit as it matures within the barrel. The spirit acts as a solvent, gradually dissolving and extracting these aromatic compounds from the charred wood. The higher the char level, the more vanillin and related compounds are available for extraction. Additionally, the char layer acts as a filter, removing some undesirable compounds and further refining the flavor profile. So, a heavy char results in a richer, more intense vanillin flavor due to the increased thermal degradation of lignin and the greater availability of vanillin precursors.