Once you’ve pumped or expressed that precious liquid gold, proper storage is crucial. If you store breastmilk correctly, it keeps all its nutrients in top-notch condition and stays completely food-safe. Improper storage or handling can damage the nutrients or even allow bacteria to grow in the milk.
Fortunately, breastmilk has strong antibacterial properties. It can be stored longer than formula.
How long can you store breastmilk?
It depends on how and where you store it. Past these deadlines, the milk is either no longer food-safe, or its nutrients start to deteriorate too much.
(These guidelines only apply to healthy, full-term infants. If your baby has any type of medical condition, consult your pediatrician or healthcare provider.)
For freshly expressed or pumped milk:
- 3-4 hours in a warm room (80-90°F)
- 4 hours at room temp (61-79°F)
- 24 hours in an insulated cooler with ice packs (59°F)
For refrigerated milk (32-39°F):
- Ideally 3 days, ok up to 8, if the milk is fresh
- 24 hours if the milk was previously frozen
Note: Store towards the back of the fridge, far away from the door—it’s colder and more consistent back there.
For frozen milk:
- 2 weeks in the back of the freezer compartment inside the fridge unit (temperature varies)
- 6 months in a freezer unit (<39°F)
- Ideally 6 months, ok up to 12 months, in a stand-alone deep freezer (0°F)
Note: After the breastmilk thaws, don’t refreeze it. If you can’t use it up in time, throw it away. Freezing kills the breastmilk’s antibodies, and double-freezing kills so many nutrients that it’s no longer a healthy choice.
How can you tell if breastmilk is spoiled?
Although you should follow the guidelines above, going past them doesn’t automatically mean the milk is spoiled. There are three big signs that breastmilk has gone bad:
- It smells terrible, like rotten milk.
- It tastes sour. (Yes, it’s ok to taste it—it isn’t weird to keep your baby safe.)
- It doesn’t mix when you swirl it.
If it smells fine, tastes like milk, and recombines easily, then it’s likely still safe to drink—but it might not be as nutritious. The longer it’s stored, the more vitamins and antioxidants are lost.
How do you thaw breastmilk?
There are two ways to thaw breastmilk: slowly and quickly.
To thaw milk slowly: Put it in the back of the refrigerator about 12 hours before you need it.
To thaw milk quickly: Put the breastmilk bag under cold running water. Slowly turn the water warmer until the milk is thawed. (Don’t use hot water, just warm.)
How NOT to thaw milk: Don’t thaw milk at room temperature. Although it might seem like a nice middle ground, it is less food-safe.
How long can you store thawed breastmilk?
It’s safe to keep thawed milk at room temp for 2 hours or in the refrigerator for 24 hours. (Start the clock once it has finished thawing.)
Don’t re-freeze breastmilk. This destroys some of the vital nutrients.
How do you warm cold or frozen breastmilk?
- Put the bag of milk in a cup or bowl of warm water and let it sit for a while.
- Use a bottle warmer.
- Use the quick-thaw method (put it under running water), just keep it under the warm water a little longer.
Don’t microwave the milk
This kills a lot of the nutrients. It also increases the risk of burning the baby’s mouth because it heats unevenly.
Don’t heat the milk in a pan
Again, too high heat risks killing the nutrients and burning the baby.
Don’t shake the milk
The milk will stratify in storage—the creamy fats rise to the top. It’s important to mix them back into the thinner liquid, but don’t shake the container. Surprisingly, shaking the milk may actually damage the protein structure of the large proteins in the milk. Baby needs those proteins!
Instead, wait until the milk is warm (it mixes better then) and gently swirl it until it looks combined.
To extend storage time, keep everything clean
If there are few bacteria in the milk to start with, then it takes a lot longer for bacteria to multiply and create unsafe conditions. So wash your hands carefully before pumping.
The breast pump, of course, should be thoroughly washed and dried between uses. Use hot, soapy water, wash in a dishwasher, or boil the pieces. If your infant is healthy, the breast pump doesn’t need to be sterilized.
(Don’t use chemical disinfectants. The chemicals aren’t good for the baby, and they’re not always as effective.)
How to store breastmilk
Store in small portions. They’re easier to thaw, and it means you’re less likely to waste any.
Write the date on the bag before you store it. Then you know whether it’s still safe and fully nutritional. (If you're sending your baby to daycare, write baby's name on the bag, too.)
Use food-grade glass baby bottles or breastmilk storage bags. Some types of plastic bottles are unsafe (especially bottles made with bisphenol A, also known as BPA—check for a number 3 or 7 in the recycling symbol). BPA-free plastic is safe, as is glass. Make sure the lid fits tightly.
Breastmilk storage bags—specifically made for storing human milk—are easy to store, easy to thaw, and easy to write the date on.
Don't use disposable bottle liners or other plastic bags. They aren't strong enough to store milk safely in the long term.
Leave about an inch empty at the top, for any storage container. Breastmilk expands when it freezes. You don’t want it oozing out! (If you do get an oozer, sadly you should throw it away. If it wasn’t fully sealed, it’s not fully safe.)
Pump directly into the storage container. The American Academy of Pediatrics explains this prevents the loss of fats and calories. They're more likely to cling to any container, so switching containers leaves some nutrition behind.
Other tips for breastmilk storage
Fresh first. The Academy of Breastfeeding Medicine suggests using fresh breastmilk before you use refrigerated or frozen milk, if both are available. Fresh milk is more nutritious than frozen milk. Frozen milk is still healthy, but some nutrients do burst when they freeze—especially IgA antibodies, which protect the baby against infection.
Fresh milk also has more antioxidants, fat, vitamins, probiotic bacteria, and protein than refrigerated or frozen milk.
For frozen milk, oldest first. The Centers for Disease Control and Prevention (CDC) recommends using your oldest stored milk first. Breastmilk slowly deteriorates, so if you leave some milk longer, it will be less nutritious.
Also, your body adjusts your milk over time to match your growing baby’s nutritional needs. The longer you store milk, the bigger the disconnect between his needs and your milk.
If the baby drank some of the milk but didn’t finish the bottle, you can save it for 2 hours.
Use the oldest date if you combine two bags of breastmilk. This ensures the whole bottle is safe and healthy.
Don’t mix warm milk and cold milk. Let the warm milk cool down before mixing.
Storing breastmilk means breastfeeding your baby longer
It might seem like there are a lot of rules, but most of them are pretty straightforward. You’ll get used to them over time until you know them backwards and forwards, and when you forget a detail, you can come back to this article for a refresher.
Storing expressed milk means you can use other childcare providers, go back to work, go on a trip, or just let other people take a turn feeding the baby. It’s a wonderful option.