If I were to mix a bunch of whey protein in the morning with milk, how long would it last? I think I read somewhere that whey will start to break down after mixing after X hours and then will not be useful to the body.
Well, seeing as it's extracted from milk in the first place, I doubt that mixing it with milk is going to do anything.
no, standard whey will be fine doing that... how long it would last (as in a reasonable amount of time before bacteria/germs would be significant) depends on the conditions though.
is it refrigerated? room temp? a lot of air in the bottle (more air = more oxidation = easier for bad stuff to grow)? etc
Yes refrigerated. I would probably fill half of my 32 oz. bottle.
You will be fine within any reasonable time (days).
Even creatine is surprisingly stable in an aqueous environment.
well if you have enough time you could freeze it then take it out and let it thaw until you want it...