Deau Black X.O. is comprised of eaux-de-vie made from grapes that have grown in the Grande Champagne and Petite Champagne regions of Cognac. Deau mature this eaux-de-vie in new oak casks, which, being untouched virgin wood, would likely infuse the Cognac with heavy wood flavours. Deau then move the brandy to older casks, which impart less tannins into the Cognac but still serve to mature the spirit. Deau Black takes its name from the colour of the tasting glasses that were used during blind tastings of the Cognac, a practice which I can only imagine is used to ensure the tasters are not prejudiced by the colour of the Cognac and instead only rely on aroma and taste.