A process for the preparation of free carboxylic acids including: A) preparation of carboxylic acid by a biological cell located in an aqueous medium with addition of an amine of formula (I) where R1, R2 and R3, independently of one another, are identical or different, branched or unbranched, optionally substituted hydrocarbon radicals or H; B) for cases where the added amine A) is water-soluble, addition of a water-insoluble amine of formula (I), where, in A) or B), a multiphase system is obtained and the corresponding ammonium carboxylate is formed from the water-insoluble amine and the carboxylic acid; C) removal of the water-insoluble phase; and D) heating of the water-insoluble phase with release of free carboxylic acid.