ANALYSIS OF LIGNIN FROM OAK CASKS USED FOR THE MATURATION OF SCOTCH WHISKEY

Wood from four types of casks used for the maturation of Scotch whisky was analysed for free vanillin, syringaldehyde, vanillic and syringic acids and for milled wood lignin. Degradation of wood lignin by acidolysis was used to estimate the proportion of intact beta-aryl ether linkages present. The yield of milled wood lignin was unaffected by repeated cask use. A comparison of acidolysis yields and the analysis of spirit matured for 3 years in each of the four types of cask indicated that the majority of beta-aryl ether linkages in oak lignin are resistant to spirit hydrolysis and that cask exhaustion was not accompanied by significant delignification. Significant reductions in the concentrations of free guaiacyl and syringyl compounds were recorded for used casks and proved the best indicator of cask exhaustion.