Ishu (off-odor)

Ishu (異臭), meaning "off-odor," refers to an unpleasant smell in sake that differs from its normal aroma. The term is used to describe disagreeable smells that are not found in properly made sake and that arise during fermentation or as a result of storage conditions. Off-odors can have a variety of causes and may take forms such as a putrid smell, a musty or moldy smell, or a chemical smell. These are regarded as signs that the quality of the sake has deteriorated. When enjoying sake, it is important that it be free of off-odors, and if you notice one, it is recommended that you avoid drinking that sake.