XO , an abbreviation for “extra old,” is a designation used on the labels of cognac and other French brandies to indicate a very mature bottling. It was first used by Hennessy in 1870. The current official requirement for XO cognac, Armagnac, and calvados is that its youngest component must be aged in oak casks for no less than ten years. In practice, many XO brandies incorporate eaux-de-vie aged significantly longer. As with VS and VSOP brandies, XO-marked brandies produced in the United States are not restricted to minimum age requirements. See vsop and vs.
Bureau National Interprofessionnel du Cognac. L’encyclopédie du Cognac. https://www.pediacognac.com (accessed March 15, 2021).
By: David Mahoney