acetaldehyde is an organic compound that is closely related chemically to ethanol, so called “drinking alcohol.” This relationship is reflected in the systemic name for acetaldehyde, which is ethanal. Although the compositional difference is slight, merely two hydrogen molecules, the impact on the way the compound smells, tastes, and feels is dramatic. Acetaldehyde smells and tastes solvent-like, with a distinct “green apple” note. In concentration, it is generally considered to be an off flavor in beer, wine, and spirits. In small amounts, however (roughly, less than 250 milligrams per liter), it is considered an important part of the flavor of some spirits, whiskies in particular, and is also thought to contribute positively to mouthfeel. It is one of the compounds whose concentration increases as a spirit ages in wood. See texture.
Acetaldehyde is an intermediate product of all alcoholic fermentations, formed in the yeast cells and then converted to ethanol by a facilitating enzyme called nicotinamide adenine dinucleotide (NAD+ or NADH). It will therefore be present in some amount in every alcoholic fermentation.
The concentration of acetaldehyde can be minimized during fermentation by providing yeast with the best possible environment to fully complete the fermentation process, which includes controlling the available nutrients, managing temperature, and selecting the appropriate duration for fermentation. Acetaldehyde is more volatile than ethanol and can therefore also be effectively removed by either a batch distillation process (with most of the acetaldehyde being removed in the “heads”) or by a continuous distillation process with a side stream that selectively removes acetaldehyde and other high-volatility compounds.
See also distillation.
Nykänen, Lalli, and Heikki Suomalainen. Aroma of Beer, Wine, and Distilled Alcoholic Beverages. Berlin: Akademie Verlag, 1983, 52–53.
Piggott, J. R. The Science and Technology of Whiskies. Harlow, UK: Longman Scientific & Technical, 1989.
White, Chris, and Jamil Zainasheff. Yeast: The Practical Guide to Beer Fermentation. Boulder, CO: Brewers Publications, 2010.
By: Nicole Austin