Vanillin is an important flavour compound in barrel-aged wines. It is formed in oak wood during barrel toasting and then extracted into wines during barrel maturation. Microbiological action in the oak barrel can then convert vanillin to the relatively flavourless derivative, vanillyl alcohol.
Previous analyses of these compounds by gas chromatography / mass spectrometry (GC/MS) have given poor accuracy. A new analytical method using GC/MS and a deuterated analogue of vanillin, d3-vanillin, as internal standard has been developed. The sample preparation requires minimal volumes of wine and is rapid. The detection limit for vanillin was 1 µg/L in red wine and the quantification curve showed excellent linearity throughout the range of 1 to 2000 µg/L with a correlation coefficient of 1.000.
The analysis has been applied to white, red and model wines stored in new oak barrels made from Vosges, Limousin, Troncais or American wood.
White and model wines were stored in oak barrels for 11 weeks. White wines completed fermentation and were stored on lees during this period. Two thirds of the vanillin extracted into white wines was removed by the fermentation and lees maturation processes. White wines were then racked off less and stored for a further 44 week maturation period. Comparison with model wine data showed that, following racking, no further microbiological transformation of vanillin took place, even though some malolactic fermentation took place during this period.
Red wines and model wines were matured in barrels for a 93 week period. Although red wines had completed alcoholic and malolactic fermentation prior to barrelling, further undefined microbiological activity in the red wines depleted the vanillin extracted from the wood by about 50%.