What are the bubbles on the surface of cooking bacon? As you can see in the picture, this bacon is just about ready to be removed from the heat.

Just what are those bubbles/foam(?) on the surface of the bacon?
Note: this is fresh bacon from a butcher-- not processed or packaged-- if that makes a difference.
I'm pretty sure that's just steam and hot air bubbling in the layer of fat/grease that's all over the bacon.