 One half remains in the bourbon barrels, while the other is transferred to exclusive 30 year old Gonzalez Byass Matusalem oloroso sherry butts before they are reunited to create this whisky.This vintage is initially matured for 12 years in American white oak ex-bourbon casks.The Dalmore 15 is then split equally between three different sherry woods; Amoroso, Apostoles and Matusalem oloroso for a further three years.