Impact of toasting oak barrels on the presence of polycyclic aromatic hydrocarbons in wine.

Toasting Quercus sp. oak wood is one of the key stages in manufacturing barrels intended for aging wines and spirits. During this operation, the increase in temperature causes variable modifications in the physical structure and, more importantly, the chemical composition of the wood. Polycyclic aromatic hydrocarbons (PAH) are high-risk molecules likely to be formed during toasting of the wood and later extracted by wine or spirits in direct contact with the barrel. In the context of an analysis of all potential sources of risk associated with the manufacture of barrels for winery use [prevention policy defined using a Hazard Analysis Critical Control Point (HACCP) approach], we carried out a preliminary study to provide a more accurate assessment of potential risks related to the presence of PAH in cooperage and winemaking. Wood toasted to different levels under different conditions, as well as wines aged in barrels made using different methods, was analyzed by gas chromatography and mass spectrometry (GC-MS) for the identification of the main PAH present, quantification of each of the molecules extracted, and estimation of any possible toxicological risks, via a comparison of values with those measured in other types of food. The results clearly showed that the heating processes associated with barrel production actually resulted in the formation of various molecules in the PAH family. However, only a minority of the target PAH presented high toxicity, particularly carcinogenic potential. Because of the specific toasting process used, benzo[a]pyrene, the best-known, and one of the most dangerous, contaminants, was not significantly present in toasted barrel wood. In view of the PAH concentrations in wood and the low solubility of these compounds, their extraction in wine is apparently relatively slow and limited. Finally, comparing the overall PAH concentrations, and particularly those of the most toxic compounds, with estimated absorption from food or the environment, we found it was obvious that the contribution of toasted barrels to the total amount was extremely low and should not, therefore, be considered a major health concern.