Taste Thresholds of Phenolic Extracts of French and American Oakwood: The Influence of Oak Phenols on Wine Flavor

Abstract

The concentration of the total phenol fraction in extracts of both green and seasoned oakwood from Ohio in the USA and from the Limousin and Vosges regions and the Tronçais forest in France was measured by both UV absorbance at 280 nm and by the Folin-Ciocalteu reagent. The concentration of phenols in both white wine and model wines stored in barrels made from the same wood samples was also measured. Taste thresholds of the aroma-stripped extracts in a white wine and in a model wine were determined by duo-trio difference testing. The concentration of the phenolic fraction in the extracts varied with oak source, but not with seasoning (i.e., wood drying). Taste thresholds varied with both of these parameters. The concentration of phenols in the barrel-aged wines was near to or below their sensory thresholds, indicating that the contribution of oak polyphenols to the taste of a wine is likely to be no more than a subtle one and to depend on the training and sensory acuity of an individual observer. The sensory thresholds of extracts containing aroma volatiles were much lower than those of the aroma-stripped extracts, suggesting that it is the oak-derived volatiles that provide the primary sensory cue that a wine has received oak-treatment.