if you wanna know what spoiled breast milk
smells like, leave a bottle with some left over milk
on the counter a few hours (eww- not that i recommend it). also, my lactation consultant told me that a baby would refuse spoiled milk.
also, freshly pumped breast milk is good at room temp for several hours. for me, during the summer, it was good up to 5 hours. in the winter, up to 8 hours during the day.