Dark sour ale aged in Leopold Bros whiskey barrels A demonic dark sour, Nightmare on Brett takes on many facets during its transformation to the sour side. Initially aged in large oak foeders with our mixed culture of wild yeast and bacteria, this beer is then transferred to bourbon and whiskey barrels. The various spirit barrels bring on a new life to this beer as it conditions for months, while obtaining additional bourbon and whiskey characteristics. Dominated by dark fruit aromas and flavors, the underlying cacao notes meld with an acidic tart berry finish. With each batch release being a unique blend of barrels, the multiple variations of Nightmare on Brett released throughout the year prove that with creativity and experimentation, anything is possible.