Why does canned produce need a hechsher?🥫

Hey, Rabbi Gutterman, why does  canned produce need a hechsher? So, on my first day at the OU, I was  taken to a vegetable canning facility,   and they did canned green beans in this  big cooker called a retort, and out came   the green beans, and then came in pork and  beans, and after that came in canned corn.   And that's why I realized very quickly why canned   vegetables need certification because they can  share the same heated equipment, the same retort.