To create The Balvenie Portwood 21 Year Old, rare 21 Year Old Balvenie - which has been matured in traditional oak casks - is transferred to a port cask, or pipe, which has held fine port wines. Here it is sampled every month by The Balvenie Malt Master to ensure that just the right amount of character is imparted by the port casks, enhancing and developing the single malt, whilst preserving its original characteristics.