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How to Store Breast Milk
February 6, 2024

How to Store Breast Milk

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How to Store Breast Milk.
How to Store Breast Milk

There’s a lot to think through when you’re pumping or expressing milk for your baby. Questions like how long fresh milk can stay out, how to freeze breast milk (and how to thaw it) and what to do with the leftover milk if your baby doesn’t finish their bottle are just a few things you might be confused about.

Feeling overwhelmed? Information overload is totally normal, especially considering all the other things you’re learning on the fly as a new parent. But knowing how to store breast milk is important, both for the safety of your baby and to maintain the quality of the milk you’ve spent so much time pumping. And the good news? Once you learn the basics and have a few weeks of pumping and storing milk under your belt, it will quickly start to feel like second nature.

How to Pump Breast Milk

Before you can store your breast milk, you’ll first need to pump it. How to Pump Breast Milk for Your Baby: Babylist’s Ultimate Guide walks you through all things pumping, including how to choose a breast pump, when to start pumping and how often to pump breast milk, how to feed your newborn pumped milk and more. Here are some tips to keep in mind as you pump:

  • There are four main categories of breast pumps: hospital-grade, electric, wearable and manual. For very infrequent pumping or occasional pumping on the go (think a night out with friends or a date night), a manual pump will get the job done; however, if you’re exclusively pumping, regularly pumping at work or pumping at least once or twice a day at home, you’ll want to invest in a high-quality double electric breast pump. If you have insurance, it’s possible to get your breast pump covered for free.
  • There’s no hard and fast rule around when to start pumping breast milk, but most lactation consultants recommend waiting about two to three weeks after birth to introduce a pump. (The exception is if your baby is in the NICU, in which case you’ll want to start pumping immediately after birth if your baby is unable to nurse.)
  • Pumping frequency and session durations look different for each person, but a good rule of thumb to keep in mind if you’re planning to both nurse and feed your baby pumped milk is to pump once or twice a day anywhere from 10-20 minutes each session.
  • Before pumping milk, always wash your hands well with soap and water, inspect your pump kit and tubing to make sure it’s clean and be sure that both your pump and the surface that you’re pumping on are clean.

Breast Milk Storage Guidelines

While there is a lot of science behind storing breast milk, there’s some nuance, too. That’s because there are a lot of factors involved; things like temperature fluctuations, room and storage temperatures and cleanliness all come into play.

These milk storage guidelines for healthy, full-term babies, based on guidance from the Centers for Disease Control and Prevention (CDC) are a good place to start.

Another easy-to-remember trick is the “rule of fours” from the American Academy of Pediatrics (AAP): four hours at room temperature and four days in the refrigerator.

Already overwhelmed? Pro tip: download, print and hang these guidelines on your fridge for quick, easy access.

Breast Milk Storage Options

According to CDC guidelines, you should store expressed breast milk in milk storage bags or clean, food-grade glass or plastic containers with tight-fitting lids. Avoid anything with the recycle symbol number seven; that indicates the container may be made with BPA-containing plastic.

Some common storage options include plastic or silicone milk storage bags plastic or glass bottles or containers and breast milk storage trays.

  • Pre-sterilized plastic breast milk storage bags are a popular milk storage choice among nursing and pumping parents. Pros: fairly inexpensive; freeze flat for compact storage; easy to transport. Cons: can leak; not eco-friendly.
  • Silicone milk storage bags are an option to consider if you’re looking for a greener, non-plastic alternative. Pros: reusable and eco-friendly; plastic-free. Cons: expensive; not as compact; time-consuming to clean.
  • Depending on the type of pump you’re using, it may be possible to pump directly into plastic or glass breast milk storage bottles. Pros: convenient, less to wash; eco-friendly; leakproof. Cons: expensive; bulky; longer thawing time if frozen; time-consuming to clean; breakable (if glass).
  • Breast milk storage trays are similar to ice cube trays—but made specifically to store frozen breast milk. They’re made from plastic or silicone, and each cube- or stick-shaped compartment usually holds about an ounce of milk. Pros: less waste as you can thaw the exact amount you need; reusable. Cons: expensive, especially if you’re storing large quantities of milk; bulky; time-consuming to clean.

How to Store Breast Milk in the Refrigerator

Per CDC guidelines, freshly pumped breast milk can be stored for up to four days in the refrigerator. Thawed milk can be stored in the fridge for up to 24 hours. Start counting the 24 hours when the breast milk is completely thawed, not from the time you took the milk out of the freezer.

Always store your milk in the back of your refrigerator where it’s the coldest. Never store it in the door—the milk may get too warm as your fridge door is opened and closed all day.

And remember, you can’t refreeze breast milk once it’s thawed, so be sure to only take out the amount you think your little one will drink to avoid waste.

How to Store Breast Milk in the Freezer

The CDC recommends storing breast milk in the freezer ideally for up to about six months, but up to 12 months is still deemed “acceptable.” That’s because although the freezer keeps food safe almost indefinitely, it’s best to follow storage time recommendations to ensure the best quality of your milk.

Like storing milk in your refrigerator, always place milk in the back of your freezer where it’s the coldest. Some parents, especially those who are exclusively pumping, may also choose to use a separate chest freezer that’s reserved just for pumped milk. Using a separate chest or deep freeze doesn’t change the storage recommendations, though; the CDC still advises the six to 12-month timeframe.

And keep in mind that breast milk expands when frozen. Never fill breast milk storage bags past the recommended amount (the maximum fill level for most bags is six ounces), and leave about an inch of room at the top if you’re storing your milk in a different type of container.

How to Store Breast Milk at Work

Pumping and storing milk at work presents its own separate set of challenges, but having some key supplies on hand and keeping a few guidelines in mind will make things go a lot smoother.

Freshly expressed breast milk can be stored at room temperature for about four hours or in an insulated cooler for up to 24 hours. After you pump at work, you have a handful of storage options:

  • If you have access to a refrigerator, you can store your milk in breast milk storage bags, bottles or containers. Look for all-in-one bags that you can both pump and feed from to save time and effort. And be sure to clearly label all of your milk using a permanent, waterproof marker.
  • If you don’t have access to a fridge (or don’t want to use the one at your place of work), you can store your milk in an insulated cooler with a few ice packs or a freezable cooler pack like a PackIt.
  • One more option: insulated breast milk coolers. These water bottle-like containers are made from stainless steel and designed to keep milk cool for 20+ hours. They’re a great choice if you don’t work in an office (think folks like teachers, healthcare workers, students or food service workers or if you’re employed in beauty or retail) or if you don’t have a refrigerator you can use to store your milk at work.

Breast Milk Storage Tips

Keep these other tips in mind when storing breast milk:

  • Whether you’re storing your milk in the refrigerator or the freezer, always clearly label it with the date, amount and your baby’s name if you’ll be bringing the milk to a daycare or sitter or if there are multiple children in your home who drink breast milk.
  • Squeeze any excess air out of breast milk storage bags before sealing them and freeze the bags flat. This makes for much more compact storage.
  • Freeze breast milk in small amounts, especially in the first few months when your baby isn’t taking a large bottle at every feeding. Storing milk in smaller quantities—about two to four ounces—will ensure less waste.

How to Thaw Breast Milk

The most important thing to remember when using frozen breast milk is always to thaw the oldest milk first. The quality of breast milk declines over time, so you want to be sure you’re using your thawed milk from oldest to newest. Want an easy way to remember this? Think “first in, first out.”

The CDC recommends a few ways to thaw breast milk:

  • In the refrigerator overnight.
  • In a container of warm or lukewarm water.
  • Under lukewarm running water.

The one thing to avoid when you’re thawing breast milk? The microwave. Microwaves create hot spots in milk that may burn your little one’s mouth and their heat can break down the nutrients in your breast milk.

A few other things to keep in mind:

  • Thawed milk can be used 24 hours from when it’s completely unfrozen. The 24-hour countdown starts when there are no longer any ice crystals in the milk, not from the time you take the milk out of your freezer
  • Once you’ve defrosted your milk, you’ll need to use it—you can’t refreeze it. The one exception is if your milk has started to thaw but still remains partially frozen. (Like in the case of a power outage, for example.) As long as there are still ice crystals present, it’s safe to refreeze your breast milk.

Another thing to remember: thawed milk can look, smell and taste different than freshly expressed breast milk. Sometimes there’s no cause for this, but other times it’s because of something called excessive lipase activity, also referred to as high lipase. (Lipases are enzymes found in all milk that support an infant’s ability to digest fats, protect against some infections and more.)

Milk with high lipase activity is completely safe for your baby to drink, but sometimes it smells and tastes soapy or fishy and a baby may reject it. There are a few things you can try, according to the La Leche League, like mixing thawed milk with freshly expressed milk or scalding the milk prior to freezing it. (This involves heating your milk to the point that it’s bubbling to the edges but not boiling.) Talk with a lactation consultant for more recommendations if you’re having this issue.

Pro tip: don’t wait until you have a freezer full of frozen milk to see if your baby will take it or not. Try thawing some frozen milk and giving it to your baby early on so you can head off any issues that may pop up.

How to Feed Your Baby Pumped Milk

Wondering if you need to heat your baby’s breast milk up to the perfect 98.6 degrees? Thankfully, no. (Collective phew.) Feeding your baby pumped milk is probably the easiest part of pumping and storing breast milk.

Breast milk can be served warm, at room temperature or even right out of the fridge and cold if your baby doesn’t mind.

  • If you do decide to warm your milk, place the sealed bag/container in a bowl of warm water or run it under running warm water for a few minutes. You can also use a bottle warmer if there’s a breast milk setting.
  • Always test the milk’s temperature on your wrist before giving it to your baby to be sure it isn’t too hot.

Since breast milk naturally separates into a milk layer and a cream layer when stored, you’ll probably need to mix your milk before serving. Go ahead and swirl, mix or shake it—it won’t damage the milk at all.

If your baby doesn’t finish the bottle, you can offer it again for up to two hours. After that, you’ll need to toss it.

Frequently Asked Questions

You’ve done your research and you still feel a little overwhelmed? That’s totally normal. Figuring out how to properly store and thaw breast milk is nothing if not a little confusing. Here are some of the most frequently asked questions you may come up with—and their answers.

My power went out! Now what?

A power outage is every pumping person’s worst nightmare if you have a freezer or fridge full of breast milk. But don’t panic, because your milk may be good for longer than you think.

Per the CDC, breast milk is safe to drink for about 48 hours if it’s being stored in a full freezer and about 24 hours if your freezer is about half full. If it’s in the fridge, you’ll get about four hours of safe storage time.

But remember: don’t open the door! Opening and closing your fridge or freezer door, even for a quick check, will bring down the inside temperature down faster. Resist the urge and keep everything shut tight.

And keep in mind that if your frozen breast milk is partially thawed but still has ice crystals, it’s safe to refreeze.

How do I store breast milk if I’m traveling?

Similar to if you’re storing pumped milk at work, it’s safe to keep your frozen breast milk in a cooler or other insulated container for up to 24 hours. Chilled breast milk that’s still within the 24-hour timeframe can then be either refrigerated or frozen.

If you plan to be away from your baby for an extended period of time, like a work trip or a vacation, check out Milk Stork. This breast milk shipping service offers domestic and international shipping for refrigerated or frozen milk. Some employers even cover the cost, so check with your human resources department beforehand.

Can I mix freshly pumped breast milk with milk that’s been in my refrigerator?

According to the CDC, you should not mix freshly pumped milk with already cooled or frozen milk. That’s because the warm milk can bring down the temperature of the stored milk. They recommend cooling fresh milk before combining it with any chilled milk that you’re storing.

Can I feed my baby expressed milk if I have thrush?

Thrush, a type of yeast infection, may grow on your nipple if you’re a nursing parent. It is safe to continue breastfeeding your baby and feed them expressed milk while being treated for thrush.

It’s also safe to give your baby milk frozen during thrush while you’re still being treated. Some sources recommend not freezing expressed milk while you have thrush for later use (because freezing milk does not kill yeast and there’s a risk of reinfection if you give the milk to your baby at a later date). There haven’t been a lot of studies on this, so it’s probably best to err on the side of caution here.


Jen LaBracio

Senior Gear Editor

Jen LaBracio is Babylist’s Senior Gear Editor, a role that perfectly combines her love of all things baby gear with her love of (obsessive) research. When she’s not testing out a new high chair or pushing the latest stroller model around her neighborhood, she likes to run, spin, listen to podcasts, read and spend time at the beach. In her past life, she worked for over a decade in children’s publishing. She lives outside of Chicago with her husband and their two boys, Will and Ben.

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