Abstract: A process for producing sorbic acid is described, by first reacting crotonaldehyde with ketene to prepare a polyester, then decomposing the polyester with hydrochloric acid, separating the crude sorbic acid from the reaction solution, and purifying the separated sorbic acid, said purifying step comprising the following steps:(a) continuously dissolving the crude sorbic acid in petroleum at a temperature in the range of from 100.degree. to 140.degree. C. while evaporating the residual water and hydrochloric acid from the solution of the sorbic acid in petroleum;(b) separating the tar content from the petroleum solution in a separation column at a temperature in the range of from 100.degree. to 140.degree. C.; and(c) subjecting the mixture of sorbic acid and petroleum to flash evaporation in a film-type evaporator at a reduced pressure in the range of from 20 to 60 mmHg, with the evaporation residue being withdrawn from the bottom of the evaporator and recycled to step (a).