The present invention relates to the field of fermentation technology. In particular the invention relates to fermentation processes for the production of a first and a second fermentation product by a single production organism wherein the first product is in a more reduced state than the substrate and the second fermentation product is in a more oxidised state than the substrate yet in a less oxidised state than the final oxidation product CO.sub.2, such that the concurrent synthesis of the first and second product in the organism allows recycling of reducing power and can be performed under (partially) anaerobic conditions. The invention also relates to such processes in which the first and second fermentation products are capable of forming a(n) (insoluble) complex or salt.