Comparative Study of the Characteristics of American White Oak (Quercus alba) and European Oak (Quercus petraea and Q. robur) for Production of Barrels Used in Barrel Aging of Wines

Abstract

Among the many species of the genus Quercus, only a few are of major technological interest for cooperage. In this work, the main structural and physical-chemical characteristics likely to affect the watertightness of the barrels and the quality of wines stored in oak wood were investigated for three different species in the Erythrobalanus section: American white oak (Quercus alba), sessile oak (Quercus petraea), and pedunculate oak (Quercus robur). Scanning electron microscope images showed that the fact that it is possible to saw-cut American white oak staves, without risking loss of watertightness, is principally due to the special structure of the thyllae in the heart wood of this species. On the other hand, European oak must always be split to avoid rupturing the vessels, as the thyllae of these species do not provide an adequate barrier against liquid seepage. Whereas European pedunculate oak has high quantities of extractable ellagic tannins, sessile oak releases much smaller quantities of polyphenols, and white oak even less. The American species have a greater aromatic potential than European oak due to their high content of cis/trans isomers of β-methyl-γ-octalactone. American white oak is easily identified by the low quantity of extractable polyphenols, the high methyl-octalactone content and the presence of two isomers of 3-oxo-retro-α-ionol. European sessile oak and American white oak are perfectly suitable for aging fine wine. Pedunculate oak, with its low aromatic potential and high ellagitannin content, is best suited to aging spirits. The quantity of extractable methyl-octalactones in American white oak is sometimes excessive and would be likely to have a negative influence on the wine's aroma. Proper control of toasting operations in barrel-making could facilitate the use of this type of oak, by modeling the release of volatile and odorous substances from the wood.