SummaryThe glucose metabolism of Saccharomyces rouxii NRRLY—1096, the soy yeast, under aerobic and anaerobic conditions, was investigated. The study was carried out at pH 4.5 and 7.0 with cells previously grown at either pH. The pH at which the cells had been grown as well as the pH at which glucose was fermented were found to affect the pattern of fermentation. A typical yeast type fermentation was obtained with cells grown at pH 4.5 and fermenting glucose at the same acid pH. An ability to fix CO2 for formic acid synthesis was demonstrated by cells grown at neutral pH. Acetic acid was produced by cells fermenting glucose at neutral pH irrespective of the pH at which they had been grown. Various schemes of glucose fermentation were therefore proposed. From results of the present study, optimal conditions for the formation of the desired fermentation products, resulting in the flavour and bouquet of good quality soy sauce, are suggested.