I used to make them. It was my job, on occassion, to trapse into the shipping department, collect expired meats, and drag them on a dolly back to the end of the plant.
Then I would take all this old meat, and dump it into a giant vat, at least twenty feet across in my imagination, where giant automatic rakes spun slowly around in this ex-meat goo. So gooey it was, that from there it was sucked up through giant pipes (12" diameter?) to an upper floor where I never ventured.