To develop a new type of sake having a refreshing sour taste, non-lactic acid assimilating sake yeasts (MLA-12 and MLA-15) that were partially deficienct in malate dehydrogenase (MDH) were isolated from Saccharomyces cerevisiae Kyokai no.901 with treatment of ethyl methanesulfonate.It was found that MDH activities of the mutants were less susceptible to catabolite inactivation by glucose than that of the parental strain Kyokai no.901.The mutants produced a relatively large amount of lactic acid but a small amount of malic acid in static YNB 10 medium.However, the mutant MLA-12 produced large amount of malic acid (90 mg/ l ) than the parental strain (60 mg/ l ) and mutant MLA-15 (40 mg/ l ) in static YNB 10+10% ethanol medium.And malate synthase activity of the mutant MLA-12 was the highest.The result of the sake brewing with mutant MLA-12 on a laboratory-scale (300 g total rice) revealed that the amount of malic acid increased in proportion to the formation of ethanol during the moromi-mashing.The sake made with the mutant MLA-12 contained two times as high concentrations of lactic acid and malic acid as that made with strain Kyokai no.901 and had a refreshing sour and flavorous taste like wine.