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Everything you need to know about breast milk storage (but probably don’t). Learn to effectively express and store breast milk.

Whether you’re going back to work, need to leave your baby with a babysitter for a few hours, don’t want to do weighted feeds for a low weight-gain baby, or just want your partner to experience some of those night feeds and snuggles, at some point during your breastfeeding journey, you’ll probably need to learn to effectively express and carefully store your precious breast milk.

We’ve put together this article to help you figure out how!

13 Things You Should Probably Know About Breast Milk Storage (But Likely Don’t)

#1 – Breastmilk storage guidelines differ by source, so read guidelines with a critical eye 

The internet is full of advice about breastfed milk storage, but the quality of advice varies – and some of it’s a bit confusing. For example, some guidelines only include the “ideal” temperatures and storage times/conditions for breast milk storing, whereas others include “less than ideal, but still okay” temperatures and times/conditions as well. 

Add to that, different guidelines define “room temperature” differently. If you’re regularly expressing milk and keeping it at room temperature for several hours, make sure your version of room temperature (which will vary greatly based on geography and season where you live) is in line with the guidelines you’re following.

Storage times and conditions also vary for fresh milk vs frozen milk, so make sure you’re following the correct guidelines based on what type of milk you’re dealing with (fresh, previously frozen, etc).

Finally, guidelines depend on how healthy your baby is. If your baby is a full-term, healthy infant, the guidelines will be different than if your baby was born pre-term or has health conditions/concerns. 

When checking online sources, try to dig a bit deeper to see if they define how they came up with the guidelines and who they’re intended for! 

#2  – When in Doubt, Remember the Rule of Fours 

The rule of Fours is an easy way to remember some baseline guidelines about how to store breast milk. The fours include 4 hours at room temp and 4 days in the fridge. 

It’s more complicated than that, but this is a good start and is easy to remember.

Generally speaking, try to use freshly expressed breast milk sooner rather than later. If you’re out for the day and have expressed milk with you, consider using a stroller organizer with insulated cup holders to store the bottle, or bring a cooler/ice pack along.

#3 – If Your Stored Breast Milk Has Gone Bad, You’ll Probably Know Right Away

Breast milk that’s gone bad is quite obvious. You’ll probably be able to smell it as it thaws or once you take it out of the fridge, as it has a very sour or rancid smell and taste.

If your milk isn’t sour or rancid, it’s probably okay. 

When you store breast milk, it can result in a different taste and odor, but that doesn’t mean it’s gone off. Some mothers mention their milk smells or tastes a bit soapy with storage (due to the enzyme lipase), but this isn’t indicative of a problem. 

#4 – The First Drops are Fine

It’s a myth that you should discard the first few drops of freshly expressed milk! 

There’s no need to discard the first few drops of milk when expressing, as some believe. It’s not any more likely to have bacteria in it than other milk that’s expressed later in the session

#5 – Fresh is Best

It’s fine to express and store breastmilk, but it’s healthiest for your baby to have mostly freshly expressed milk. 

When you need to store it, it’s healthiest for your baby to make the fridge your main spot for breastmilk storage (rather than the freezer). That’s because many of the leukocytes / white cells in human milk are destroyed by freezing. Similarly, Vitamin C levels decrease over time with freezing

If possible, try to give mostly fresh, then refrigerated, then frozen breast milk 

Date and label everything, so you know when it expires.

#6 – You Don’t Need to Sterilize Bottles and Containers for Breast Milk 

If you’re feeding your baby formula, you need to sterilize baby bottles before every use. However, that’s not the case with containers for human breastmilk. While you need to ensure they’re clean, dismantling them and using hot water and baby dish soap to wash them, and then letting them air dry completely or using paper towel to dry them, is enough. Using a dishwasher with natural detergent to clean is also good.

#7 – Milk Shaking is Controversial – Seriously 

When storing breastmilk, the cream naturally rises to the top during storage, so you need to mix it somehow to distribute the fat before feeding your baby. 

Some breastmilk storage guidelines caution against shaking breastmilk because it might denature the proteins and change the nutritional value. 

We couldn’t find any scientific studies to back this theory up, and we did find articles suggesting you’d need A LOT of force (more than most of us would use to shake a bottle) to damage the proteins. 

We’ll leave it up to you – if you land on the side of the anti-shakers, then mix up the milk with gentle swirling instead.

#8 – It’s okay to combine!

It’s okay to combine milk from different pumping sessions into one container, however the milk should be the same temperature when combined. Don’t add freshly expressed milk into an already refrigerated container of milk. 

When storing combined milk, calculate the expiry date from the oldest milk.

# 9 – You shouldn’t directly heat human milk

Microwaving breastmilk or heating it on the stove destroys some of its best parts in terms of nutrition and immunological benefits 

To thaw frozen breast milk, put it in the fridge overnight or run warm (not hot) water over the sealed container, or place the container in warm water.  

Warm frozen or refrigerated milk slowly. This will ensure you preserve the most beneficial components.  

#10 – Containers Matter

When storing breastmilk in the fridge, store it in a food-safe plastic! The leukocytes / white cells in human milk adhere more to glass bottles than to plastic. You want your baby to consume those white cells, so avoid refrigerating milk in glass so you don’t lose white cells to the container. 

Conversely, when freezing breastmilk, you want to freeze it in glass. Overall, glass isn’t as porous as plastic, and freezing destroys many of the leukocytes / white cells anyway. 

Don’t use stainless steel containers for storing breast milk. They are associated with a decline in cell count and viability when compared to plastic. This means an overall decrease in milky goodness.

Whatever container you choose for your breast milk storage, you’ll need to stay on top of cleaning. After each use, take it completely apart and wash in hot soapy water or in a dishwasher. Thoroughly dry it prior to putting it away.

Using specially designed breastmilk storage bags made for this express (pun intended) purpose is a good idea. These sturdy bags have places to record the date and little increments for milk measurement.  

#11 – Pay Attention to Container Numbers 

If using plastic to store your breastmilk, check the recycling number. 

Recycling code 5 indicates it’s made of polypropylene, a food grade plastic that’s generally considered safe.

Recycling codes 3 and 7 indicate the plastic may have BPA or BPS, so you’ll want to avoid those ones.

#12 – Leave Space at the Top

Breast milk expands when frozen, so you need to leave room at the top of the storage container. Experts recommend storing in batches of 2 to 5 ounces. Think about how much your baby eats per feeding, and store in small batches to minimize wastage.

#13 – Simply refrigerating or freezing milk isn’t good enough 

When it comes to storing breast milk, you need to be fairly scrupulous in terms of where you store it.  

Sticking a bottle of breast milk on the fridge door won’t cut it. Constantly opening and closing the fridge door can affect milk quality and safety. 

Same goes for a freezer – a small freezer in a refrigerator is opened and closed all the time. Compare this to a separate deep freeze, which stays consistently cold and is opened far less often. Frozen milk in a fridge freezer can be kept for less time than one in a deep freeze.

So how can you protect that white gold when refrigerating and freezing?

Store milk in the back of the fridge and away from the door to ensure consistent temperature. In the case of a refrigerator freezer, store the milk away from the door. In the middle and at the back is best.

Guidelines for Safe Breastmilk Storage

Follow these simple storage and preparation techniques in order to protect the health and wellbeing of your little one at feeding time. 

  • Wash your hands with soap and water before expressing.
  • Gather everything you need before you start, including clean containers, a nursing cover if needed, etc.
  • Inspect pumps and tubing to ensure they are clean and clear. Dispose of and replace any moldy tubing, and follow the manufacturer’s instructions for adequate sterilization between uses.
  • When storing, use appropriate containers. Use food safe plastics with a securely fitting lid. Breastmilk storage bags are specifically designed for this purpose! They also have a place to record the date and time, as well as volume measurement markings. 
  • Avoid plastic that contains BPA (recycle number 7), as well as stainless steel. When refrigerating, avoid storing breast milk in glass.
  • Only fill containers to three-quarters full to allow for expansion.
  • Clearly record the date and time that you have expressed the milk onto the container.
  • Expressed breast milk is safe for 4 hours at room temperature (less than 77 degrees) in temperate climates. Your milk is also good for 4 days inside the fridge, 2 weeks in the freezer compartment inside a fridge, 3 months inside the freezer of a 2-door fridge/freezer and 6-12 months inside a deep freezer. 
  • You can also keep fresh milk safely inside a cooler bag for up to 24 hours with ice packs if you are going away.  This is great for peace of mind for traveling.  After 24 hours, the milk needs to either be used, or refrigerated/frozen.
  • Store your milk is kept deep within the fridge or freezer, where there are few temperature fluctuations. Never store your breast milk near the door of the fridge/freezer. 
  • When thawing frozen breast milk, always use your oldest frozen milk first. 
  • Never use the microwave to thaw, instead place the bag inside a container of lukewarm water or under running warm water. 
  • Never refreeze thawed breast milk.  Discard any milk at the bottom of the bottle after a feed.

Final Thought: Getting Started with Breast Milk Storage

By following these simple guidelines your little one can securely enjoy expressed breast milk, and you will have peace of mind knowing they are still receiving optimal nutritional benefits.  

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