Enhanced substrate conversion efficiency of fermentation processes

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 less oxidised state than the final oxidation product CO2, 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 further relates to processes in which the first fermentation product is weak alkaline compound and the second fermentation product is a weak acidic compound. In such instances both products may be produced by a single organism in a single fermenter or each the first and second product may be produced by two different organisms that are co-fermented. Co-fermentation may be performed in two separate fermenters that are connected through micro-sieves that allow circulation of soluble medium components between the two fermenters but prevent circulation of the production organisms' cells. 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.