Influence of toasting technique on color and ellagitannins of oak wood in barrel making

The toasting of oak affects some of the most important flavors contributed by barrels to wine. The specific effects of some manual coopering techniques have not been well studied. In a preliminary investigation, we compared the effect of heat source, which also affected air supply, and the use of water in the toasting process. The temperature during toasting was monitored, and the wood was analyzed by colorimetry and for its content of gallic and ellagic acid and the tannins vescalagnin and castalagin. While water usage decreased toasting temperature and affected color inconsistently, it did not have a large effect on the content of the extractable phenolics. A limited air supply resulted in lighter oak color despite higher toasting temperatures and almost total loss of the original ellagitannins. These observations should be corroborated by additional studies to separate the effect of heat versus air supply as well as effect on oak aroma components and the resulting sensory effect.