ketone is an organic compound characterized by a carbonyl group attached to alkyl or aryl groups. Ketones can be produced by the oxidation of secondary alcohols (such compounds include aldehydes, esters, and other flavoring and aromatic compounds). See oxidation. Some in Cognac believe that ketones are partly responsible for many characteristic aromas of rancio in cognac.
Particular ketones found primarily in very old aged cognacs are now linked to specific aromas and flavors such as green banana and fruitiness (2-butanone); coconut and herbs (2-nonanone); rose, iris, and pineapple (2-undecanone); and mushrooms, coconut, and chicken fat (2-tridecanone).
There is much that is not yet understood about these characteristics and even the sources of these ketones: current thinking is that fatty acids may be altered during fermentation to provide conditions for ketone development. There has been little comparable research among other aged spirit industries, though it may be that similar compounds develop in similar ways in other aged spirits such as whisky or rum.
American Chemical Society website. https://www.acs.org (accessed April 18, 2016).
By: Doug Frost