Frozen vegetables (Passover) Status: Q. Why do frozen vegetables require Pesach certification? A. Frozen vegetables sold as “raw” are in fact cooked for a few minutes, in a process known as “blanching”. Some of the factories which blanch vegetables also blanch pasta/chametz, and therefore frozen vegetables should only be used with Pesach hashgachah. This guarantees that the vegetables were not cooked on equipment which had been previously used for chametz.