Dewar's is a pioneer in the process of "double aging," with all the blends in the series undergoing a secondary rest in oak barrels to combine the flavors and bring extra smoothness to the blend. With the new limited edition series "Double Double," this process has become an art form, with a "quadruple aging" process created by Dewar's master blender, Stephanie Macleod.

The process includes:

• The malt whiskies reach the required age and are blended, returning to an oak barrel.
• The grain whiskies follow the same process.
• Both types of whiskies are blended and returned to an oak barrel for a secondary double aging period.
• The blend is finished in an ex-Sherry cask.

This 21-year-old release was finished in Oloroso Sherry casks, offering "subtle notes of cinnamon and ripe vine fruits with a silky smooth finish."