Aldehydes

aldehydes, a class of chemical compounds midway between the alcohols and the organic acids in their state of oxidation. They are formed during any phase of processing in which an alcoholic beverage is exposed to air. acetaldehyde is the aldehyde of most interest to wine producers. Some aldehydes have quite potent odours, even if they are usually present in only trace concentrations in wines and spirits. As such, aldehydes contribute harmoniously to the overall character.

Those aldehydes containing more than the two carbon atoms of acetaldehyde are in general much more palatable. Vanillin, for example, is a complex aromatic aldehyde present in the vanilla bean and in many other plants, including some grapes where it is present as a glycoside and is a flavour precursor. Vanillin also occurs as a component of the lignin structure of oak wood. If new oak casks are used for wine maturation, some of this vanillin is extracted from the wood into the wine, where it may add complexity to the flavour. (See also oak flavour.)