Quick food science question, and yes, I *did* poke around a little before posting I promise. I had a clean out the fridge dinner-for-one last night and wanted to throw together a sauce for some frozen tortellinis. I had some fresh mushrooms and frozen peas/carrots etc.. so went "cream sauce" route rather than "red sauce" route. Alas... no cream! No half and half! So I could make a milk based bechamel foundation.. maybe go overboard on the butter component.. but HEY.. LOOOK! A fresh pint of buttermilk I hadn't used... and a hunk of Maytag blue cheese to melt into it! That's going to be tangy, creamy goodness!
Technique: Olive oil... saute some prosciutto scraps... add some garlic... then mushrooms and saute until they give off their liquid and the sauce tightens back up... then I add the frozen peas/carrots and get this warmed up...<smugly feel proud of my skillz> and here comes the buttermilk... and then... YUCK!! It separates immediately! The milk solids curdle up and I have a soupy, murky, gross looking mess. I try to re-constitute it with the blue cheese chunks melting in but it's a lost cause. It didn't taste much better than it looked.
So I assume that the acidic properties of the buttermilk caused the separation / curdling (anyone who has ever added cream to a wine-based sauce too aggressively knows what I'm talking about) but why is buttermilk "stable" in the fridge and yet separates with a bit of heat? If I had brought it to a boil, etc... I wouldn't question.. but this was immediate upon pouring into the pot.
Hopefully someone learns from my mistake!