Duff beer was a beer produced on Simpson's Planet that could cure llhrei'sian on Romulans. Its alcoholic content was 11 Proof (5.5% abv) and was rather brown in coloration. (RIS Bouteina) Vox'ula realized that Duff beer was a cure for the llhrei'sian induced by Krusty burgers, after drinking it. Also, Homer Simpson was fond of Duff beer and could tell between replicated and fresh Duff beer. ("What about some D'oh!")