Sunday’s Whisky is aged 3-9 years at cask strength in mostly ex-bourbon casks, with some whisky being aged in port, sherry, and wine casks to allow Yamaguchi-san to perfect the blend utilizing the varying flavors that each cask has imparted. The diurnal temperature shifts of Koriyama allow the casks to expand and contract to accelerate the process of aging. The whisky is then blended before adding the pristine, alkaline water from the nearby springs of Koriyama.