The effects of size, temperature and air contact on the outcome of heating oak fragments

The concentrations of the important oak aroma volatiles guaiacol, 4-methylguaiacol cis- and trans-oak lactone and vanillin in extracts of French and American oak heated under various conditions were measured using stable isotope dilution analyses coupled with gas chromatography-mass spectrometry. Heating resulted in marked increases in the concentrations of guaiacol, 4-methylguaiacol and vanillin, with more formed at higher temperature. Approximately twice as much guaiacol and 4-methylguaiacol and two to five times as much vanillin were formed by heating in the presence of air compared to heating under argon. Oak lactone concentration was less affected by heating. The effects of heating different sized oak pieces were investigated for French and American oak samples. Compared to heating larger oak pieces, heating smaller fragments of oak generated up to twice as much guaiacol and 4-methylguaiacol and two to four times as much vanillin at 235oC for both French and American oak. This effect is ascribed to the exposure of a greater surface area of oak to air when smaller fragments are heated. Variable effects were observed for cis- and trans-oak lactone. Variation in chip size, as well as heating time and temperature, is clearly one way of obtaining different aroma profiles from oak products.J.I. Campell, M. Sykes, M.A. Sefton and A.P. Pollnit

Changes in the concentration of volatile oak compounds and esters in red wine stored for 18 months in re-used French oak barrels

Studies were made of changes in concentration of oak-wood-derived volatiles and the evolution of esters in red wine during storage in twice-used French oak barrels. Wine samples were taken after 8, 10, 12, 15, and 18 months maturation in the barrels. Results showed that most of the volatile compounds extracted from the wood (furanic compounds, volatile phenols, lactones) reached maximum concentration between 10 and 12 months of barrel storage. After 18 months of maturation many of the compounds showed concentrations similar to those found after 10 to 12 months. However, the concentrations of furfural, 5-methyl furfural, furfuryl alcohol, coniferaldehyde, acetovanillone and phenol in wines aged for 18 months were lower than those reached after 10 to 12 months. The concentration of the ethylphenols increased right up to 18 months of ageing, which can only have a negative impact on the quality of the wine. There were few modifications in the concentration of esters, except for ethyl lactate which reached peak concentration after 12 months maturation and decreased thereafter