Dewar's Double Double 21yr Blended Scotch - 375ml#2 Whisky Advocate Top 20 Whiskies of 2019 Dewars new series of blended Scotch whiskies was created using an innovative four step aging process named Dewars Double Double. The four step maturation process involves marrying single malts together in an exhausted Bourbon cask for up to six months. A selection of grain whiskies is also married together in separate exhausted casks, before all the whiskies are blended together and rested in more exhausted