PURPOSE: To improve the quality and yield of Japanese SAKE, by stirring the unrefined SAKE with a gas having a composition satisfying the stirring condition without causing the destruction of the unrefined SAKE, thereby carrying out the normal fermentation of SAKE.

CONSTITUTION: The stirring operation of unrefined SAKE in the fermentation process of Japanese SAKE is carries out as follows. The fermentation gas generated from the unrefined SAKE is collected in the chamber 1 above the surface of the unrefined SAKE, and excess fermentation gas is discharged. The residual gas is introduced to the compression pump 4, replenished with oxygen by mixing with fresh air supplied from the line 9, and recycled to the bottom of the fermentation tank through the closed loop circuit 5, 8. The unrefined SAKE is stirred by this procedure, and normal fermentation can be achieved. Since the gas generated in the fermentation process contains CO2 and ethanol as the main components, it can be recycled and used as an efficient stirring medium without causing the surplus of oxygen, and the ethanol which is an effective flavor component can be condensed and recovered resulting in the improvement in the quality and the yield of SAKE.