Differentiation of bourbon whiskies using gas chromatography and cluster analysis.

Abstract. -- The practice of counterfeiting liquors in drinking establishments is common today. In order for a forensic scientist to help prevent this from occurring, a database of chromatographs must be compiled of all the spirits available. In this study, five brands of bourbon were analyzed and cluster analysis was applied to the gas chromatographic data. The cluster analysis showed the least expensive brand and the most expensive brand to have the greatest differences, but the three other brands formed one large third group. These groupings showed that one can distinguish one brand of bourbon from another. This study should prove useful to consumers and distillers to help in the detection of counterfeit liquors.

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There have always been attempts to adulterate spirits, for instance by blending high-quality distillates with ethanol made from a cheaper raw material, by adding synthetic volatile components to natural alcohol or by misleading labeling of the variety and origin of the raw material used. The practice in drinking establishments of placing an inexpensive brand of liquor into a well-known expensive bottle is quite common. To prevent this, research must be performed and a database compiled of each of the varieties of liquors. Then, using a portable gas chromatograph, a forensic scientist could go to an establishment and test the sample on site. This counterfeiting seems minimal, but it is costly for the major distilleries. Thus chemists need a simple method for distinguishing among various types of aged whiskeys. One such aged whiskey is bourbon. Chemists over the years have been attempting to analyze the differences in brands of bourbons, using various methods.

Gas chromatography (GC) is generally the method of choice for alcoholic beverage analyses, but the complete profile is quite complex and difficult to interpret. The volatile components, other than ethanol, are contained in what is known as the fusel oil fraction. Fusel oil is a collective term applied to the alcoholic fraction of whiskey, or high wine, with a higher boiling point than the ethanol-water azeotrope. Fusel oil usually includes n-propanol, 2-methyl-1-propanol, 2-methyl-1-butanol and 3-methyl-1-butanol in various concentrations. Individual components of fusel oil are not usually used to distinguish bourbons. This study was carried out to distinguish among bourbons using GC analysis of the fusel oil components combined with hierarchical cluster analysis.

Capillary GC with a flame ionization detector has proven to be very effective in separating fusel oils and the resulting chromatograms show excellent separation of the …