Many breastfeeding moms pump their breast milk to give to their baby when they are away. Here’s how to safely store, defrost, and warm your breast milk.

How Do I Store My Breast Milk?

You can freeze and/or refrigerate your pumped (or expressed) breast milk. Store it in clean bottles with screw caps, hard plastic cups that have tight caps, or nursing bags (pre-sterilized bags meant for breast milk). When freezing, it’s best to store breast milk in 2- to 4-ounce (59.1 to 118.2 milliliters) portions rather than larger portions so none goes to waste.

It's helpful to label each container with the date when the milk was pumped (and your baby's name if the milk is going to childcare providers). 

How Long Can I Store My Breast Milk?

For healthy full-term infants:

• You can store it at room temperature:
  • for up to 4 hours (at no warmer than 77°F, or 25°C)
• You can store it in the refrigerator:
  • for up to 4 days at 32°–39°F (0°–3.9°C)
• You can store it in the freezer (be sure to leave about an inch of space at the top of the container or bottle to allow for expansion of the milk when it freezes):
  • for up to 2 weeks in a freezer compartment located inside the refrigerator
  • for up to 6 months in a freezer that's self-contained and connected on top of or on the side of the refrigerator and is kept at 0°F (–18°C). Store the milk in the back of the freezer, not in the door.
  • for up to 12 months in a deep freezer that's always –4°F (–20°C)

You may find that different resources have different recommendations on how long you can store breast milk at room temperature, in the refrigerator, and in the freezer. Talk to your doctor if you have any concerns or questions.

How Should I Defrost Frozen Milk?

You can thaw frozen milk in a couple of ways:

• Put it in the fridge for a day (it takes 24 hours to thaw), then warm by running warm water over the bag or bottle of milk. Bottle warmers are also available to warm up milk. 
• Remove it from the freezer and place it in a bowl of warm water or run warm water over it until it's at room temperature or lukewarm. 

Never microwave breast milk. It can create "hot spots" in your breast milk, which can burn your baby’s mouth. The heat can also destroy important nutrients and proteins like antibodies, which help protect your baby from illness.

Once thawed, use the milk within 24 hours. Do not refreeze it. When your baby starts to drink from the bottle, use it within 2 hours.

My Thawed Milk Looks or Smells Different. Is This OK?

Breast milk that's been frozen or refrigerated may look a little different from fresh breast milk, but that’s OK. It's normal for early breast milk to look kind of orange and the mature milk to look slightly blue, yellow, or brown when refrigerated or frozen. And it may separate into a creamy looking layer and a lighter, more milk-like layer. If this happens, just swirl it gently to mix it up again.

Thawed milk may smell or taste soapy due to the breakdown of fats in the milk. The milk is still safe to drink, and most babies won't have a problem with it. If your baby doesn't like it, the milk can be heated to scalding (bubbles around the edges) right after it is pumped or expressed and then quickly cooled and frozen. This switches off the enzyme that breaks down the milk fats.

How Do I Clean Bottles And Pump Parts?

Before their first use, wash and then sterilize the nipples, bottles, and washable breast pump supplies (for example, the breast shields and any other part that touches your breasts or your milk) by boiling them for 5 to 10 minutes. Check the manufacturer's directions for how long to boil the parts.

You also can sterilize the parts with a countertop or microwaveable sterilizer, but boiling works just as well and costs nothing. After that, wash the bottles, nipples, and pump supplies in hot, soapy water (or run them through the dishwasher) after every use.