- “Stuffy smell”; isovaleraldehyde smell
An unpleasant smell arising when unpasteurized sake is stored at room temperature. Its root components have been identified as isovaleraldehyde , ethyl isovalerate and iso-varelaldehyde diethyl acetal . The first of these is the primary cause of mure-ka, with the other two contributing compound aromas. Isovaleraldehyde is produced during maturation by the enzymatic oxidization of isoamyl alcohol.
The following prevention strategies can be given.
- Storage at sub-zero temperatures.
- Removal of enzymes by ultrafiltration and ori-sage (fining).
- Yeast selection (avoiding yeasts which produce isoamyl alcohol in large quantities).