In Japanese sake the existence of diacetyl is a remarkable feature of its most common putrifaction so-called ‘Hi-o-chi’. By this reason alcohol for beverage use is required absolutely free from diacetyl in this country. The authers defined in this experiment the occurrence of this constituent is not induced by the normal action of yeast but the certain bacterial contamination and appointted that the careful preparation of the more microbiologically pure mash is essential for decreasing diacetyl content of the product.