I'm making my first bone broth and am a little confused by the directions I've read that say to skim off the "scum" that collects on top of the broth while simmering. I have in fact skimmed some of this off, but I'm worried I'm actually skimming off the healthy fat, which I want to keep. Can anyone out there clarify for me whether I should be skimming and, if so, how to tell the difference between the "scum" and the fat? Thanks in advance.
The "scum" is excess blood/meat protein that coagulates once the water/meat juice heats up. The scum rises almost immediately after coming to a simmer - at which point you would skim it off.
The fat takes a while to render out - you won't find a thick layer of it this soon in the stock cooking time. So you don't need to worry that you'll be ladling it off.
The scum is skimmed off to produce a clear, not cloudy, stock. So if you don't care about looks, you don't need to skim.