At the moment, it’s a pea soup with pork and ham, but it happens every time I make a soup or boil meat. Someone I knew once told me that the scum is the hormones and antibiotics that are generously used in moden agribusiness, but that doesn’t seem likely to me. What the heck is that gross stuff?
Relatives? 
Seriously, I would guess proteins.
And fat, which melts out of the meat and floats to the top.
A former coworker at one of my jobs in high school maintained that the scum was made of hallucinogens placed there by higher-ups in the soup business. :rolleyes: In fact, the answer is much more mundane: it’s coagulated proteins and fat. Not too dissimilar to a fine spray of scrambled eggs on your soup Yechhh.
Yechh indeed! Still, I’m glad to know it’s not some weird chemicals. And as for your former coworker’s idea, I always thought you had to pay extra for them to put hallucinogens in your soup.