I am unsure about this. I know once LO starts drinking breast milk from a bottle that I've pumped, I should not put it back in the fridge for later use because bacteria could have gotten in....but what if (like today), i take a bottle out of the fridge and it is in my bag for 4 - 5 hours, but he never drank from it? (I ended up feeding him from my boob when we were out). Can I then put it back in the fridge and use it another day?