The Balvenie Single 21 years old malt. To create The Balvenie Portwood Year Old, rare 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.