Q) and how can I tell if my mash has gone bad?
A) As long as you use good cleaning and sanitization methods you should have no issues- Also I recommend fermenting the mash in a food grade fermenter with an airlock. If you see anything “funky” of if the smell is terrible those are two easy ways to spot a bad mash.
Q) How long can I keep the mash before I run it?
A) As long as you have an airlock on your fermenter you can keep it for a while. If you plan on leaving the mash for over a month I would recommend racking the mash to a secondary fermenter to get it off the yeast cake.
Thank you for this info Jimmy. When you stated to rack the mash to another fermenter to get it off the yeast cake.
I have a drain on the bottom of the fermenter, do you mean to drain the mash and discard whatever is floating on top?