In another thread (https://cheftalk.com/threads/xanthan-gum-sauce-white.95382/#post-569344) I was struggling with xanthan gum. Now the mystery is deeper and more serious. I made stock by roasting and then pressure-cooking a turkey carcass. Strained and chilled, it is medium-brown, mostly clear, and semi-gelatinous: it pours, but is definitely syrupy. If I heat this to a simmer, remove from heat, and start puréeing with an immersion blender, it foams up creamy white almost immediately. Once foamy, it doesn't settle out without lots of time and fine straining. Any theories?