The Knappogue Castle 21 Year Old Single Malt Irish Whiskey is a marriage of two single malts distilled in copper pot stills and then matured in ex-bourbon casks one for 23 years (put into barrel in 1994) and another for 21 years (put into barrel in 1996) before blending them together. This expression is bottled at 92 proof and is non-chill filtered.