How to Store Breast Milk: Best Practices & Knowing What NOT to Do

We’ve all been there – rushing out of the grocery store, mom-bun disheveled with bags in tow, dashing through traffic, dreading every approaching traffic light, and running through the front door because the baby is up and hungry before your intricately timed 45-minute grocery trip is up.

Breastfeeding can be hard, and only a lucky few disagree with that sentiment.

The early weeks, especially, require 24/7 availability and there’s no knowing when the next bathroom break would be possible, let alone something as luxurious as a shower or – low and behold – coffee with friends to regain some semblance of sanity.

Having a stash of properly stored breastmilk is any breastfeeding mom’s dream. It definitely was mine.

Be it to go back to work as an exclusively expressing mom, or to gain a degree of precious freedom for a couple of hours, knowing that your baby can still benefit from your liquid gold when not attached to you is a great feeling.

But, here’s the thing: storing breastmilk requires some thought and great care. After all, there’s nothing sadder than having to throw away milk that you painstakingly pumped in between feeds.

This article will go through everything you need to know to about storing breastmilk properly, helping you ensure that your baby is only ever receiving safe and nutrient-rich milk.

The Best Way To Store Breastmilk

There are multiple ways to store breastmilk safely, depending on when you intend to use the expressed milk.

For starters, refrigeration is better than freezing if the plan is to use the milk in a couple of days. Frozen milk does lose some of its nutrients when frozen – but on the whole, it still remains more nutrient-rich than formula.

Authors of ABM Clinical Protocol #8: Human Milk Storage Information for Home Use for Full-Term Infants, Revised 2017 note that although some of the milk’s health properties change with storage, there is good evidence that storage can be safe and allows the child to be provided with optimal nutrition when breastfeeding or when immediately expressed milk is not possible.

In the hierarchy of best breastmilk, and as indicated by Stanford Children’s Health, fresh breast milk contains the most active anti-infective properties, followed by refrigerated and then frozen milk.

What you need to keep in mind here is that, while appropriate storage methods are very important, how the milk has been expressed and through which method is also key.

Studies have shown that milk that contains fewer bacteria at the time it is expressed, develops less bacterial growth during storage and actually has higher protein levels when compared to other milk that does contain bacteria.

Expressing Breastmilk For Storage

Whether your plan is to refrigerate or freeze, you should take utmost care when expressing milk.

As noted by Eglash, Simon and The Academy of Breastfeeding Medicine, as long as appropriate steps are followed, there isn’t much of a difference in terms of contamination between milk expression by hand and by a pump.

Here’s what to look out for when preparing to up your milk stash.

Doing It Safely

Here are the steps to follow once you’re ready to start expressing and want to do so safely:

Step #1: Wash your hands thoroughly with soap and water for 20 seconds. Dirty hands can transmit viruses and bacteria into the milk.

Step #2: Assemble the clean pump kit on a clean surface, taking good care to check for any soiling or mold.

Step #3: Check that pump dials and power switch are clean.

Step #4: Express milk.

Once you’ve finished expressing:

Step #1: Store milk safely (which we’ll be discussing in detail throughout this article).

Step #2: Clean pumping area.

Step #3: Take apart pump kit parts and inspect.

Step #4: Carefully clean, sanitize and store your pump equipment. Pump kits can be cleaned either by hand or in the dishwasher if recommended by your pump’s manufacturer.

Take care not to wet parts which should not come in contact with water. Air dry thoroughly on a clean surface. If you used a washbasin and bottle brush to clean your pump kit, wash these too.

The CDC recommends sanitizing pump parts at least once a day for extra protection, especially if your baby is still under three months of age, was born prematurely or has a weakened immune system.

The pump kit, washbasin, and bottle brush can be either steamed or boiled.

Always check the manufacturer’s instructions to be sure which parts can be sanitized.

Step #5: Once all pump parts are dry, wash hands thoroughly, reassemble and store in a clean area.

Should I Clean My Breast Pump Before Expressing?

Yes, your breast pump must be thoroughly clean.

Any breastmilk and breastmilk residue on your pump can quickly lead to germs. Any signs of mold in the tubing or other pump parts means that the tubing or part must be replaced.

It’s best to follow the manufacturer’s instructions when cleaning your breast pump – but, generally speaking, these are the steps to follow:

Step #1: Each part of your breast pump should be rinsed clean after use and washed with soap and water. Rinse with hot water.

Step #2: Sanitize the parts indicated as safe for sanitizing on the manufacturer’s instructions, if your baby is less than three months old, was born prematurely or has a compromised immune system.

Step #3: Allow to air dry on a clean surface, away from dust and before re-assembly and use.

Step #4: Only clean the tubing if it has been in contact with breastmilk.

Step #5: A thorough wipe down of the outside of the pump ensures that no nasty germs have made it their home.

How To Store Expressed Breastmilk Safely

Once you have your expressed liquid gold, store in breast milk storage bags, or clean glass or food-grade plastic containers with tight-fitting lids.

Label each container with the date it was expressed to make it easier for you later on when selecting which to use first.

If the milk is to be consumed at childcare or a babysitter’s, add your child’s name and any other details you need to add in to make sure no confusion whatsoever happens.

Also, include the name of any medication you might be taking. This is super important!

When filling up the containers, leave an inch of space on top, since breast milk expands as it freezes.

Protecting breast milk from temperature changes means that storing it in the door of the refrigerator or freezer is a big no-no. Due to all the constant opening and closing, that area of your fridge or freezer experiences the most temperature fluctuations.

It also helps to have a plan as to when you intend to use the expressed breast milk. If you don’t think you’ll be using it within four days, freeze immediately. This ensures that you are freezing quality milk.

There’s nothing worse than throwing away painstakingly expressed milk! Freezing in small containers of 2 to 4 ounces, or whichever amount that you know your baby usually drinks, helps to make the most of your precious stash.

As emphasized by Stanford Children’s Health, milk intended for a high-risk baby should not be frozen once it’s been refrigerated for more than 24 to 48 hours.

Containers For Storing Breast Milk

When it comes to storage container choice, interestingly – and as noted in the ABM Clinical Protocol #8 – the fat percentage reduces significantly and total protein and carbohydrate concentrations increase with either glass or polyethylene, polypropylene, polycarbonate, or polyethersulfone bottles and bags.

Still, as noted by Stanford Children’s Health, containers made of glass or hard plastic are the best for storing breast milk, especially if the intention is to freeze for use later on.

If you’re using breast milk storage bags instead, use two bags over each other to avoid ending up with any split seams from freezing. Squeeze out the air from the top of the bag before sealing tightly an inch away from the edge of the milk to allow for expansion. When done, place the bags upright in another container to avoid spillage.

Can I Store Breastmilk In Any Container I Find?

No. As noted by the Centers for Disease Control and Prevention (CDC), bottles with the recycle symbol number 7 should not be used for such purposes whatsoever. Such a marking indicates that the container may have been made with BPA-containing plastic.

Steer away from disposable bottle liners or plastic bags that are not specifically made for storing breastmilk, as these are more likely to rip or leak.

How Long Can I Store Breast Milk For?

The CDC has a general, sort of “one size fits all answer” timetable for the storage of breast milk.

Nonetheless, important factors such as milk volume, the room temperature at the time of expression, changes in refrigerator and freezer temperature and the level of cleanliness of the environment come into play and can affect the safety of the stored milk.

Breast Milk Storage Guidelines

Countertop, at room temperature

77°F or colder






0°F or colder

Freshly Expressed or Pumped Up to 4 hours Up to 4 days Ideal – within 6 months

Acceptable – up to 12 months

Thawed, previously frozen 1-2 hours Up to 1 day (24 hours) Do not, under any circumstance, refreeze breast milk that has already been thawed
Left over from a feed Use within two hours  


Adapted from “ABM Clinical Protocol #8: Human Milk Storage Information for Home Use for Full-Term Infants”, Revised 2017; as it appears on the Centers for Disease Control and Prevention Website.

Stanford Children’s Health goes a bit further in terms of guidelines for frozen milk.

If your freezer is a compartment within your refrigerator, milk should only be stored for two weeks. For freezers that are part of the refrigerator but have a separate door, you can leave milk in there for three to six months. Separate, deep freezers can keep milk in good condition for up to 12 months.

Is It Safe To Pump And Store When Away From Home?

If you’re pumping at work, on the road or while traveling, pack an insulated cooler bag with frozen ice packs. You can then store the expressed breastmilk for 24 hours in this bag.

Once you’re at home or arrive at your destination, use the milk immediately. If not, quickly store in the refrigerator or freezer.

Why is There A Time Limit On Freezer-Stored Breast Milk?

While freezing keeps food safe almost indefinitely, as the CDC notes, following these recommended storage timelines is imperative to ensure that you’re giving your little one milk of the best quality.

Pumping and Storing Breastmilk For a Premature or Sick Baby in Hospital

As noted by the CDC, if your baby was born prematurely or has specific health concerns, you should always discuss things with your healthcare provider first. Healthcare providers may provide more recommendations and instructions to ensure that your expressed milk is always pumped safely.

The Royal College of Nursing emphasizes that all health care professionals should promote, protect and support breastfeeding. Apart from professional and up-to-date advice and support, staff will also provide instructions on expressing and handling expressed breastmilk.

Moms who cannot breastfeed their babies because of prematurity or illness should express breastmilk between 8 to 10 times a day to establish a good supply and ensure that their infants are getting the best nutrition possible.

Hand expression, a manual pump or an electric pump are all good methods for expressing breastmilk for your premature or unwell baby.

Generally, hospitals suggest the use of a sterile collecting kit to use with a breast pump. Ideally, milk is expressed directly into sterile bottles and stored in the same bottles. If the quantity is too little, sterile syringes and occlusion caps are used for storage.

Each container should be labeled with the name of the baby, the name of the ward, date, and time of expression, as well as a note with required details if the mom is taking any medications.

What Not To Do When Storing Breastmilk

  1. Do not store milk that has been expressed with an unclean or moldy pump.
  2. Do not store milk in the freezer door or refrigerator door.
  3. Do not store breast milk in disposable bottle liners or plastic bags intended for general household use.
  4. Do not use containers that aren’t BPA-free.
  5. Do not add warm freshly expressed breastmilk to already chilled or frozen milk.
  6. Do not heat up frozen breast milk rapidly. Rapid heating affects the milk’s antibodies.
  7. Never refreeze thawed breast milk.

Can I Add Freshly Expressed Breast Milk to Already Stored Breast Milk?

According to the Mayoclinic, freshly expressed breast milk can be added to refrigerated or frozen milk that you expressed earlier on in the same day.

However, the fresh milk should be thoroughly cooled before being added to your existent stash. You can do this by placing the fresh milk in the refrigerator or a cooler with ice packs. Once it’s cool, you can then add it to previously chilled or frozen breast milk.

On the other hand, adding warm breast milk to already frozen milk is very bad practice. This may cause it to partially thaw, making it unsafe for your baby.

Does Refrigerated or Frozen Breast Milk Still Contain all of its Vitamin C?

Research undertaken by Buss, McGill, Darlow, and Winterboum shows that stored breast milk starts to lose out on Vitamin C after a certain period of time, and this only gets worse the longer its stored.

In a sample study, total vitamin C levels decreased on average by one-third when the milk was stored in the refrigerator or the freezer for one month.

After two months of freezing, the decrease was of two-thirds.

This led the authors of this study to recommend a change in human milk storage practices or the consideration of vitamin C supplementation if storage is a must.

How to Thaw Frozen Breast Milk

Use the oldest milk first. Always remember the rule that says: First in, first out.

Labels with clear dates on them should make this easy and leave any of the risky guesswork out of the equation.

The container that has frozen milk should be placed in the refrigerator overnight. According to CDC guidelines, breastmilk should be used within 24 hours of being thawed in the refrigerator – this means 24 hours starting from the time it is no longer frozen.

If this is not possible, warm the milk gently by placing it under warm running water or in a bowl of warm water. Ensure that the container remains properly sealed while warming.

Keep away from the microwave or a fast stove, as heating frozen breastmilk rapidly can affect its antibodies. Apart from this, heat spots in the milk can burn your baby.

Before feeding your baby, test its warmth first to make sure it’s good to go, and swirl it to mix the fat as it may have separated during storage.

It’s also interesting to note that, as indicated by the CDC, breast milk does not actually need to be warmed up. There is no rule set in stone that says babies need to drink warm breast milk.

It can be served at room temperature or even cold, as long as baby accepts it that way. But, that’s the thing – most babies won’t accept a bottle unless it’s warm.

Remember The 24 Hour Limit

We know it hurts to do this, but thawed milk that has not been used within 24 hours should be thrown away. Not doing so would be putting your baby’s health and wellbeing at risk.

Milk that has been brought to room temperature or warmed after storing in the refrigerator or freezer should be used within 2 hours at most. If not, it’s straight to the bin (as painful as this is).

What To Know About Differences In Color

You may notice that your thawed breastmilk looks different from your freshly expressed one.

As noted by the Mayoclinic, the color of breastmilk varies according to diet. Storage also gives it a different odor or consistency.

If your baby does not want anything to do with your thawed milk, shorten the storage time.

How Do I Know Whether Or Not My Stored Breast Milk is Still Good?

On this we can agree: throwing away expressed breastmilk that’s still good should be a crime. It’s only natural to want to be extremely sure that you’re not throwing away breast milk that is still great for baby, especially after everything you went through to make it.

Here are some eventualities and signs which should tell you that your liquid gold may no longer be a keeper and you should consider tossing it away:

  1. It has been stored for longer than the guidelines indicate.
  2. It has been inappropriately stored (either in refrigerator or freezer door or in containers that were inadequately sealed).
  3. Refrigerator or freezer was subject to temperature fluctuations.
  4. Pumping gear or storage container was unclean.
  5. Breast milk smells and tastes sour.
  6. When swirled, it does not return to one homogeneous consistency and fat solids float on top
  7. It has developed black or dark green mold
  8. Chunks appear in the thawed breastmilk
  9. Your baby is refusing it
  10. You’ve heated it once already
  11. It has been left on the counter more than three hours on a hot day
  12. It was expressed when you were on medication deemed unsafe for breastfeeding mothers
  13. It was expressed after alcohol consumption

What Should I Keep In Mind When Storing Breastmilk?

The longer breast milk is stored for, the more it loses out on its nutrients.

Added to this, breast milk expressed when your baby is still a newborn will not meet all their needs once he or she is older. So, if you’re thinking about putting together an impressive stash for years to come, it doesn’t exactly work like that.

As we’ve also seen in this article, storage guidelines for babies born prematurely or babies who are unwell may differ than those for babies living in normal circumstances. In such cases, you should follow your care provider’s specific instructions.

Properly Stored Breastmilk: A Unique Treasure Trove

There’s a certain unmatched pride that comes with a freezer stocked with your own milk – and an even greater level of satisfaction knowing that your little one is getting all the nutrients their body needs, thanks to yours.

For those who wish and successfully manage to breastfeed their babies, having a good stash in the freezer provides sweet peace of mind for times when life gets too hectic or you’re away from baby for a while – and a degree of independence that’s often quite hard to come by.

Following safe and proper storage guidelines and safe expressing methods ensures that your baby is still getting mom’s best! How’s that for a goal?

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Medically Reviewed By: Michelle Roth, BA, LCCE, IBCLC

Medically Reviewed By: Michelle Roth, BA, LCCE, IBCLC

Michelle Roth, BA, LCCE, IBCLC is a board-certified lactation consultant for two busy pediatric practices. She is a former La Leche League Leader, Lamaze Certified Childbirth Educator, and Certified Infant Massage Instructor. She has taught classes ranging from healthy pregnancy, to childbirth preparation, to parenting, and more.

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