I actually can't find the answer to this on google: I pumped milk, kept it in the fridge for 9 hours. Warmed it up, expecting baby to wake up, it was out for 3 hours, baby never touched it. Can I put it back in fridge and re-use or do I need to toss it? If I can put back in fridge, how long can I keep it in fridge?
I read somewhere (Dr. Sears website) that if your baby does not finish the bottle, the breast milk should still be good until the next feeding. In your case, considering since baby hasn't even touched it, it should be good until the next feeding.
After you warm it you should not refrigerate it again. It should be disgarded within an hour to two. It will breed bacteria...as hard as it is to throw milk out.
There is no recommendation from the la leche league, but many parents and dr.s agree that it might be fine since mothers milk has antibodies unlike formula which can spoil. I personally reuse it, if it smells okay and it wasn't out long.
Re: Breastmilk question
The Australian breastfeeding brochure