What Is Rancio and How To Detect The Flavor In Whisky

July 18, 2024 –––––– Jonny McCormick, , , ,

Rancio is an ephemeral and unusual aroma, and a complex constellation of flavors that have been described within a flavor spectrum that includes rather unpleasant terms like rancid butter, funkiness, mustiness, and old cheese, to more appealing ones such as woody, gamey, nutty, musty, and damp earthiness. Often there are elements of mushroom, walnut, soy sauce, truffle, tobacco, polished leather, candied fruit, and overripe tropical fruits in the mix as well. The term is borrowed from the Spanish word for stale, old, or rancid. But some of those most negative descriptors are better applied to old wine, because it’s a flavor note that most people find appealing in whisky.

Rancio is most often found in well-aged scotch whiskies, especially those at 40 years and older that have spent decades maturing in old refill sherry casks. It’s also possible to pick up hints of rancio in relatively old single malt whiskies matured in subtropical conditions, like the warehouses of southern India and Taiwan, where there is an annual angels’ share loss of 8-10%, high oxidation, and a lot of interaction with the oak.

A compound called 3-methyl-2,4-nonanedione, or MND for short, indicates the level of oxidation in red wine. Scientific analysis at Seguin Moreau, a leading cooperage in the Cognac region, found that levels of MND are higher in oxidized red wines, with their detectable MND above sensory thresholds. This might make the difference between a fruity, floral red wine and one that expresses notes of rancio.

Rancio can also be found in old tawny ports, ancient Madeiras, and aged cognacs matured for generations in damp, dark cellars. Analysis of the headspace aromas above cognac has identified other probable origins of rancio, including 2-heptanone and 2-nonanone, which slowly form from the long-chain fatty acids in oxidative environments, and may be further modified by reactions with some of the esters, as well as becoming more pronounced as other compounds evaporate. In scotch and other whiskies, however, there is little published research into the science of rancio. The organic chemistry might be similar, or it might not, but after all, what’s wrong with a little mystery in the glass?