I'm not sure what material it's on to keep it heated. But something like coal I assume.
I would imagine this is what any industrial ice cream production that's making pints for grocery store freezers would look like.
Are perpetual stews sanitary? I'm probably misjudging, but the idea of anything being out in the open for that long makes me uneasy. I guess it's kept at a simmer, so bacteria can't grow?