Vanillin, syringaldehyde, coniferaldehyde, sinapaldehyde, scopoletin, and ethanol lignin were found in both whiskey and neutral spirits aged in various types of white oak cooperage. Data obtained indicate that the mode of development of these congeners is similar for both whiskey and spirits, the amount formed depending upon the type of cooperage used and proof of distillate being aged. Experimental evidence was obtained which supports that from the literature in indicating that these aromatic congeners can arise from chemical reaction between the ethanol and components of the oak wood (charred or uncharred)-i.e., lignin-under the acidic conditions (pH 4 to 5) imposed by the barrel. The concentrations of other congener groups formed in both types of alcoholic products stored for 18 months in new charred barrels were similar.

A study was made to determine which congeners are derived from ethanol during maturation of whisky. Radioactive ethanol-1-14C was added to a barrel of new bourbon whisky and the radioactivity of the major individual congeners was determined during the maturation period. During 56 months of maturation, ethanol was transformed into acetic acid, acetaldehyde, ethyl acetate, and ethanol lignin as indicated by their radioactivity. No radioactivity was found in the solids, fusel oil alcohols, or the aromatic aldehydes derived from ethanol lignin. The chemistry of maturation is discussed.

The color intensity and congener concentration of bourbon whiskies matured for 12 years decreased as the entry proof increased from 109 to 155°, except for fusel oil content which remained approximately constant. The average annual cumulative evaporation loss rates, in per cent of original proof gallons/year, were approximately the same at all 6 proofs, i.e., 3.0%/year or 3 6% for the 12 year period. The relative rates of formation of total barrel-derived material, a newly proposed parameter defined as the sum of the increase in volatiles and nonvolatiles in an aged product, were quite similar for comparable time intervals regardless of entry proof. There was greater variation among the relative rates of formation of individual congeners at the different entry proofs. Although all congeners except esters attained at least 5 0% of their ultimate (twelfth year) value during the first 4 years, it appears that appreciable congener development continues at least through 12 years. Esters developed linearly over the 12 year period.

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