I'm planning a big barley wine and an undetermined small beer from the second runnings. I would like to maximize energy and water use and use the hottest chiller water from the barleywine to produce the second beer. Are there potential consequences for leaving the grain as is for the couple of hours it will take to get the water ready?
I recall an article in BYO that claimed tannins were extracted anytime the mash was exposed to air. The piece was savaged by batch spargers and supposedly some follow-up experiments were done, but I never saw any.