Handling and storing breast milk

Breastmilk is a fascinating substance. It provides not only all the nutrients that your baby needs, but it also has specific antibacterial properties that helps it to stay fresh and which also helps to limit the growth of bacteria.

In this respect, it is entirely different from formula, which is not a living substance and doesn’t have any of those antibacterial properties.

The guidelines for storing breast milk compared with formula are very different. 

If you are expressing your breast milk by hand or by pump, it’s essential to know how to handle and store breastmilk safely.

One of the first things to remember is to wash your hands before you express your milk.

This simple measure will significantly limit the growth of bacteria in your milk.

What kind of containers do you need for expressed milk?

Many women have tried to express milk into a bottle and found it to be quite tricky, as the milk spurts out of the nipple in many directions, making it difficult to catch.

It can be useful to use a wide-mouthed jug or bowl to catch the milk.

This container can be either sterilised or put into your dishwasher to clean before collecting the milk.

You may also use hot soapy water to wash the container beforehand, and then rinse it and let it air dry before you collect your milk.

Breast milk in a bottle and storage bags

Once you’ve collected your milk, it’s then really important to store it either in the fridge or freezer in a sterilized container.

You may wish to consider using leak-proof food storage containers or plastic bottles that have a tight, secure lid.

It’s also possible to use specially made freezer bags made especially for breastmilk.

Always remember to label and date the milk so that you can use the oldest milk first.

How you store your breastmilk

Storing your breastmilk will depend on how soon you want to use it.

If you need to use your milk immediately, you can express your milk and leave it at room temperature for up to six hours.

Some literature suggests that even up to eight hours may be safe, but six hours would err on the side of caution!

This fresh milk can be given straight to your baby.

If you want to keep your milk for a few days, it’s far better to refrigerate it than to freeze it.

Freezing will destroy some of the anti-infective properties (although not all), but refrigeration is a far better option.

Your breast milk can be kept at the back of a fridge if your fridge is between 0-4 degrees (centigrade).

It can be kept for up to five days and still be given fresh to your baby.

If you are going back to work and you don’t have access to a refrigerator, or if you are out and about with your baby and want to transport breast milk, you can store it in a cool bag or box that has deep-frozen ice packs in it.

The ice packs would need to be changed every 24 hours, but this gives you great flexibility.

You can store breast milk in a freezer that is minus 18 degrees centigrade, and can be kept for up to 6 months and given to your baby.

Although freezing will destroy some of the properties in breastmilk that help to fight infection, it’s still the healthiest choice for your baby compared to formula.

If freezing your milk, it’s always best to express, and then to store it in the freezer straight away.

Leave a little gap at the top of the bottle or freezer bag to allow for expansion of the milk when it’s frozen.

Some mothers store their breast milk in ice cube trays, in very small amounts, kept in a sealed container, or perhaps an ice cube tray with a lid, so that they could use the small amounts of breast milk to mix with baby foods when needed – a fantastic idea!

Breast milk in a bottle and storage bags ready for freezing

Another useful tip is if you are expressing your milk, you can add to the same batch over 24 hours.

For example, if you only manage to express a small amount, e.g., 20ml here and a small amount there, if you chill the milk for an hour, you can add it to an already chilled amount that’s in the fridge.

Keep adding it to the same batch over 24 hours. Some women will leave the pump in the fridge too so that they don’t have to keep re-sterilizing it over the 24 hours.

It can be useful to store your milk in 60 to 120ml amounts. When babies feed at the breast, they tend to take about that amount per feed.

Saving your milk in smaller quantities like this will mean there will be less wastage.

Some mothers become concerned when they see their milk separating into two distinct parts, a creamier part, and a more watery part, but don’t worry, this is entirely normal.

Gently swirl the milk a little bit and then give it to your baby; it’s fine.

Sometimes I’m asked about the smell or the taste of the milk. Some say that the milk tastes or smells soapy.

This is related to the breakdown of fats within the milk, and it is perfectly safe for a baby to drink.

Is it possible for your milk to go off? 

The truth is that it CAN go off. If you think that your milk smells rancid or tastes like cows’ milk when it goes off, then it shouldn’t be given to your baby.

Very occasionally, a breastfeeding woman will tell me that even when she stores her milk for a very short period, the milk smells rancid.

An overactive amount of the lipase enzyme in the milk which breaks down milk fats is usually the cause of this, and it can be a problem. 

Thankfully, there is a way you can deactivate the enzyme.

Frozen breast milk

This involves expressing your milk and then immediately heating it to the point where you can see bubbles around the edge (but not boiling the milk).

The milk is then immediately cooled and frozen, which will deactivate the enzyme.

Another important point is if you or your baby are being treated for a thrush infection, you can carry on breastfeeding.

You can also express during the treatment time. 

It may be that you freeze the milk or refrigerate it. Any of that expressed milk can be given to your baby WHILE you and your baby are being treated.

However, refrigeration or freezing doesn’t kill the yeast, so once the treatment has finished, you must discard the expressed milk.

Giving your baby your refrigerated milk

You have several options. The first one is to offer your baby milk straight from the fridge without warming it up at all.

Many babies will be happy to drink the milk – it doesn’t always need to be heated up.

Secondly, you may wish to warm it by running it under a warm tap, gradually warming the milk up, and bringing it to room temperature.

Thirdly, you may wish to warm it up by placing the container in a bowl filled with hot water from the kettle or the tap, which will gradually warm it up.

Milk must never be heated up in a microwave (even to defrost it) as this can be dangerous for your baby due to hot spots that can occur.

If you have frozen milk which you wish to defrost, it is far better to let it gradually defrost in the fridge overnight.

Once it’s thawed, you can leave it in your fridge for up to 24 hours. However, it’s important to give it to your baby within that time.

If, however, you find yourself in a hurry, you may need to defrost the milk quickly.

In that scenario, you can run it under the tap, under cool water, and then warm running water, or you may wish to stand it in a bowl of hot water and defrost it a little bit faster.

Sometimes, there are questions where there isn’t clear evidence for a concrete answer. For instance, ‘if my baby doesn’t finish a bottle of breast milk, can the milk be given to my baby later?’

Based on what we know about breast milk and after considering other lactation specialist opinions, I would suggest that it could be refrigerated again and given within one to two hours.

Some suggest that it could be left longer than two hours, but until we have reliable research, it’s always best to err on the side of caution.

Review dates, references & further resources

Review Dates

Version 1.1 published in March 2019. Next review date: Jan 2022


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