Cask types Brazilian Amburana oak casks impart exotic notes to aged spirits, including tobacco, cedar and cinnamon. Rolling Fork uses responsibly harvested full Amburana oak casks for this aging (no Amburana oak chips or inserts!) Aging whiskey in Amburana casks can be a challenge. To preserve the character of the rum, Rolling Fork aged the rum for six months in Amburana casks and then racked the rum to hand-selected, low-char, heavy-toast bourbon and rye whiskey casks for additional aging.