I cant see a problem with storing the runnings. I would just make sure they are well mixed before you boil the next day. also saving the runnings shouldnt be bad just as long as you dont have any husks left in there. I dont know what them sitting chilled would do but I would be worried about tannin extraction just like with boiling grain
I've gone as long as 24 hours without refiregating or freezing...just collect the runnings in a sanitized bucket with a sealing lid, and let them sit.
Not sure I'd push it much beyond that, though. Even though the subsequent boil will kill any nasties, it won't stop them from creating off-flavors in the meantime.
Storing mash runnings
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