Dewar?s Double Double 21 Year is a blended scotch crafted by master blender Stephanie Macleod which is aged in a ?four stage aging process.? The first step involves single malts and single grains which have been aged separately at least 21 years. Next, the single malts are blended together and rested in exhausted casks. This process is also done for the single grains. Then, the blended single malts and blended single grains are blended together and again rested in exhausted casks. Finally, the blended scotch finishes its maturation in sherry casks. For the 21 year, it is finished in ex-oloroso sherry.