The Effect of Kiln-Drying on the Levels of Ellagitannins and Volatile Compounds of European Oak (Quercus petraea Liebl.) Stave Wood

Abstract

The study examines the effects of kiln-drying on the composition of ellagitannins and volatile compounds in different layers of sessile oak wood cut from staves destined for use in the fabrication of barrels. Four drying regimes are compared, two of which combine air-drying with kiln-drying at 40°C or 65°C, and two regimes which involve only kiln-drying at 40°C or 65°C. The level of ellagitannins either remains constant or declines only slightly during drying, depending on the quantity of free water in the staves and the physical state of the wood. It is the area of the bole from which the stave is cut, relating to the age of the wood, that has the greatest influence on the level of ellagitannins. Among the volatile compounds, one observes a sharp decline in the levels of ß-methyl-γ-octalactone (without any change in the isomer ratio), eugenol, 3-oxo-α-ionol, and linoleic acid. This decline is greater when the temperature of drying is raised. Kiln-drying at 65°C produces an increase in the levels of furfural and hydroxymethylfurfural which may be explained by a slight degradation of xylane and glucomannan fractions of hemicelluloses.