Gas Chromatographic Determination of Ethyl Esters of Fatty Acids in Brandy or Wine Distillates

¹ Department of Viticulture and Enology, University of California, Davis, California 95616.

The ethyl esters of fatty acids containing even numbers of carbon atoms, particularly caproic, caprylic, capric, lauric, myristic, and palmitic acids, are characteristic components of distilled alcoholic beverages such as brandy, rum, and whisky. The most abundant esters in brandy are usually those of caprylic (C₈), capric (C₁₀), and lauric (C₁₂} acids. A method was developed for quantitative determination of these three esters by gas chromatography. Sample preparation consisted of taking 100 ml of sample, diluting with water to 20 vol % alcohol, extracting four times with methylene chloride, and removing solvent from the combined extracts. Two microliters of a known volume (5 ml) of the concentrated ester extract, with ethyl pelargonate added as an internal standard, was chromatographed on a 6-ft x 1/8-inch FFAP column programmed from 100 to 225°C at 7.5°C per minute. Ratios of individual esters to pelargonate peak height were compared with those for known standard ester solutions for quantitative determinations.

Typical continuous-still beverage brandies distilled from fresh wines with suspended yeast cells contain 2 to 3 mg of caprylate, 5 to 10 mg of caprate, and 5 to 8 mg of laurate per 100 ml. Comparable distillates obtained by continuous low-temperature (vacuum) distillation or by simple batch distillation contained less. The levels of these fatty acid esters in brandies were markedly reduced when yeast cells were removed from the wine prior to distillation. The formation of esters by yeasts during fermentation, possible distillation variables affecting the concentrations, and their probable significance in brandy are discussed.