An offensive aspect of a beverage, such as rotten egg (Hydrogen sulfide) odor, or an atypical aspect, such as a Cabernet-Sauvignon wine smelling or tasting more like a Pina Colada can be described as "off". Usually this is indicative of some kind of flaw or fault. (Wine,Beer,Spirits,Sake,Mead/Tasting Terms Chemistry & Flaws)