Store your breast milk in a glass or a BPA-free plastic container that's clear in color (so you're sure it's dye-free). Plastic storage bags work too, as long as they're made for breast-milk storage (regular plastic zipper bags can be weak and leak). Freshly pumped milk can stay at room temperature for up to six hours and will keep in your fridge for up to seven days. According to the Centers for Disease Control and Prevention, you can freeze breast milk for up to three to six months in a regular freezer, or up to 12 months in a freestanding deep freezer. Slow-thaw the milk in the fridge for 12 hours, or submerge the frozen milk in a cup of warm water to speed up the thawing process. Remember, never microwave a bottle—it can remove some of the milk's nutritional value or overheat the bottle, risking a burn to baby's mouth.