The process for producing amino acids from volatile fatty acid (VFA) molecules, termed precursors, produced by anaerobic fermentation from fermentable biomass, comprises at least the following steps: - a) extracting the volatile fatty acid (VFA) molecules, without interrupting the fermentation, using an extraction means chosen from means which are, at least, insoluble in the fermentation medium, - b) collecting, outside the fermentation reactor, the volatile fatty acids (VFA) molecules once extracted, - c) synthesizing a given α‑halogenated acid, by halogenation, from a type of volatile fatty acid (VFA) chosen from the volatile fatty acids collected in step b) and defined according to the type of amino acid desired, - d) synthesizing a defined amino acid from this α‑halogenated acid.