A process for the solid-phase synthesis of salts of organic acids in a granular, free-flowing, and dust-free form particularly suited for use as animal feed additives. A mixture of liquid organic acids, including butyric acid, is applied to an inert, absorbent carrier. A solid base is then added during stirring. The acid is slowly released from the carrier preventing the fast reactions that lead to the formation of clumps. The exothermic reaction releases heat which assists in reducing the moisture content of the product. The addition of butyric acid results in a product which has an improved effect on animal growth over the animal feed additive without the addition of butyric acid.