Rubber smell

Simply the unpleasant smell deriving from rubber. It arises when heated sake is transported using new rubber hoses, or when sake is left in contact with rubber bungs or seals for a long period of time.

It is also thought that the sulphide-like smell caused by the decomposition of sulphur-containing amino acids (amino acids containing sulphur atoms) like methionine and cysteine may be a cause of  gomu-shu , and a rubber-like smell is sometimes found in shinshu which has fermented well. In some cases, too the odour of fusel and other oils may give a rubber-like impression.