The tannins of oak heartwood: Structure, properties, and their influence on wine flavor

Barrels used for the aging of wines and spirits are constructed from oak he artwood. Heartwood tannins (soluble polyphenols) are the most abundant of t he constituents of oak wood that are potentially extracted into the wine du ring aging. The structure and properties of these compounds are reviewed, a s are methods of analysis. Studies of the natural variation in the concentr ation of heartwood tannins are summarized and show that levels are highly v ariable within and between individual trees and especially between wood pro venance and species. Despite the abundance of heartwood tannins and their s olubility in the wines, the concentration in oak-aged wines is generally lo wer then expected and their influence on wine flavor remains uncertain, Dif ferent studies and hypotheses concerning the influence of oak tannins durin g wine aging are reviewed and conclusions drawn on our current understandin g of their role.