With the cover on, a heavy insulator wrapped around it the steam will build up in the head space, as more steam at say 151 is added it condenses the steam cloud more, the molecules all of a similar temperature condensing will begin to raise the temperature in the headspace as they condense further (ie building pressure). Eventually the heat will transfer back into the grain bed (Think pressure cooker only not nearly as much pressure or heat, you heat it to boiling but the steam heats it beyond boiling)
I'm a bit tipsy but I think that explains it pretty decently
Yup,like I said it's all about thermodynamics. The coat also has an insulated hood on it. I put two pot holders down on the spread out inside of the coats' back,then pull the hood over the covered pot (BIAB),then wrap the sides around that & tie it off with the sleeves. It gets insulated really well. With the paint strainer bag wrapped over the lip of the kettle,the lid gets sealed a bit that way too.
Oh man,I can't wait till my son gets back from work with that vodka. My nerves need to be numbed a bit with these hurtin joints.