AbstractA method is introduced which makes a continuous oxidation of glucose to glucose acid possible. This method is based on the auxiliary‐substrate concept and co‐metabolism, respectively. Micro‐organisms (e.g. Acinetobacter calcoaceticus), which cannot assimilate glucose, but merely oxidize it, are grown continuously on a heterotrophic substrate (e.g. acetate). While growing they simultaneously synthesize gluconic acid. The productivity of the gluconic acid synthesis with a given strain depends on the dilution rate and the mixing proportion.Since growth and product synthesis are closely connected and growth yield is very much higher due to an auxiliary substrate effect in the presence of glucose than on the heterotrophic substrate alone, this method is suitable for SCP production as well. The productivity of gluconic acid production is controlled at a certain dilution rate by the mixing proportion of the growth substrate and glucose.