Rokashu (filtration odor)

Rokashuu (濾過臭), or filtration odor, refers to an unpleasant smell transferred to sake from the materials used during the filtration process. This odor can arise from the characteristics or condition of filter media such as filter paper and activated charcoal. For example, if the filter paper is old or not properly stored, impurities and off-odors from the paper can pass into the sake. Excessive use of activated charcoal can also allow the charcoal's own distinctive smell to affect the sake, producing an odor known as charcoal odor (tanshu). Because these filtration odors harm the quality of sake, they must be carefully managed during production.