To create The Balvenie PortWood Aged 21 Years, a marriage of rare Balvenie is transferred to port casks, or pipes, which have held fine port wines. Here it is sampled regularly 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. In duty free The Balvenie PortWood Aged 21 Years is non chill-filtered and bottled at a higher strength of 47.6% abv. - balvenie.com