Formic Acid Formation in Alcoholic Fermentation.

The possible occurrence, origin, and role of formic acid in alcoholic fermentation has been a particularly controversial subject. KRUIS and RAYMAN (26) observed formic acid in fermented liquids and attributed it to a direct action of air upon some constituent of the wort. The majority of the investigators who have observed the presence of this acid in fermented liquids, however, believed it to play some role in the fermentations of sugar by yeast. Among these were LIEBERAMANN (27), KITICSAN (23), DUCLAUX (5), KHOUDABACHIAN (22), THOMAS (37), FRANZEN and STEPPUHN (16, 17), KOSTYCHEV (25), ESAU (9), and JOSLYN and DUNN (20). Formic acid or formate utilization by yeasts has also been reported by DUCLAUX (5), THOMAS (37), FRANZEN and STEPPUHN (16, 17), FRANZEN (14), and NEUBERG and TIR (30). On the other hand, PAKES and JOLLYMAN (33) failed to detect any formate utilization by yeasts. Formate utilization by bacteria has been well established by OMELIANSKY (31), FRANZEN et al. (12, 13, 15), GREY (18), anid PAKES and JOLLYMAN (33). DUCLAUX (5) suggested that yeasts produced formic acid when grown under unfavorable environmuental conditions. Formic acid was considered as an intermediate in alcoholic fermentation according to a theory developed by WOHL (44) and extended by SCHADE (34). EHRLICH (7, 8) favored the WOHL-SCHADE hypothesis, although he suggested that formic acid could be obtained from amino acids, ammonia, and also an aldehyde of the next lower acid in the particular series being formed. L6IB (8) objected to SCHADE'S hypothesis on the basis that the latter's reactions occur under entirely different chemical conditions than are required for alcoholic fermentation. FRANZEN and STEPPUHN (16) reported that there was initially a slight accumulation of formic acid and subsequently a decrease in media containiingr formates. This, however, does not constitute evidence, as they believed, for its role as intermediate in alcoholic fermentation (10). NEUBERG and KERB (29) testing the SCHADE hypothesis, failed to obtain alcohol from mixtures of formates, acetaldehyde, and yeast. KOSTYCHEV (25) did not regard formic acid as a fermentation product, but rather as a product of endogenous metabolism of the cell. THOMAS (37) inclined toward the view that the production of formic acid is intimately bound up with the breakdown of sugar but OPPENHEIMER (32) did not believe that formic acid played any role in normal alcoholic fermentation.