"Breastmilk is not spoiled unless it smells really bad or tastes sour.
To thaw milk
Thaw slowly in the refrigerator (this takes about 12 hours – try putting it in the fridge the night before you need it). Avoid letting milk sit out at room temperature to thaw.
For quicker thawing, hold container under running water - start cool and gradually increase temperature.
Previously frozen milk may be kept in the refrigerator for up to 24 hours after it has finished thawing. Do not refreeze.
To warm milk
The cream will rise to the top of the milk during storage. Gently swirl milk (do not shake) to mix before checking temperature and offering to baby.
Heat water in a cup or other small container, then place frozen milk in the water to warm; or
Use a bottle warmer.
NEVER microwave human milk or heat it directly on the stove.
If baby does not finish milk at one feeding, it may be refrigerated and offered at the next feeding before it is discarded."