Storing breast milk: all our tips

To store breast milk, start by washing your hands thoroughly. Rinse the containers with cold water first, then wash them with warm soapy water. You may use a suitable, fragrance-free soap. Rinse them again and leave to air-dry without wiping.

There are generally 3 methods for storing breast milk. We detail the practices below. 

Storing breast milk at room temperature

If you express your milk but wish to wait a little before giving it to your baby, you can leave it at room temperature after expressing, provided it is kept in an airtight container.

Breast milk can be kept for 4 to 6 hours at between 19°C and 22°C (up to 8 hours according to La Leche League), without risk of bacterial growth. It is best to stay under 4 hours to be safe, or in the case of a newborn.

If you change your mind and want to keep it cooler, that is possible, but the milk must not have been left out for more than 2 hours. Breast milk storage times are not cumulative.

Storing breast milk in the refrigerator

Place your breast milk in the refrigerator as soon as possible after expressing. It can be stored at 0 to 4°C for 48 hours. Ideally, it can be kept for up to 72 hours, and a maximum of 8 days according to La Leche League. In that case, milk collection must be carried out very carefully and the baby must be in good health.

Avoid placing your containers in the refrigerator door, which tends to be less cold due to repeated opening.

Storing breast milk in the freezer

For practical reasons, it is best to store milk in small quantities (less than 120 ml), varying the volumes stored. This will allow you to defrost only what you need to feed your baby. Thawed milk can be kept in the refrigerator for 24 hours, or at room temperature for 1 hour, and must never be refrozen.

Separately frozen milks can be combined, but frozen milk must never be mixed with milk at room temperature.

Do not fill your containers to the brim, as breast milk expands in volume when it cools.

Also remember to label your containers clearly with the date of expression and the volume, using a non-toxic marker.

Please note that storage times also vary depending on the type of freezer used. You can only store milk for 2 weeks in a simple frozen food compartment of a refrigerator, and up to 3-4 months in a three-star compartment. In a freezer (-18°C), milk can be kept for 4 to 6 months (4 months is ideal, 12 months maximum under very careful collection conditions, according to La Leche League).

Place breast milk preferably at the back of the freezer, where the temperature is most stable, and avoid the door where temperatures fluctuate more.

Also check that your containers are suitable. Some non-adapted glass products can shatter. Our breast milk storage bags are ideal — BPA-free, made from high-quality silicone, and easy to label with the date.

Another tip is to fill small ice cube trays with breast milk (closing the lid properly), which allows you to defrost small quantities at a time. 

Storing breast milk on the go

If you express your milk at work, you can bring it home by keeping it in an insulated bag (such as a lunch bag) with an ice pack inside. Do not exceed 1 hour of transport. Up to 24 hours in a proper cool box.

Make sure to cover the thread of your breast pump with cling film to prevent any leaks. 

If you use plastic bags, make sure to squeeze out the air before sealing the bag for better preservation.

If there is a change in taste or smell due to lipases

Expressed breast milk can take on a different taste and smell after deep-freezing. The lipases in the milk can cause this. The nutritional benefits of the milk remain unchanged and it is safe for your child, but they may refuse it. 

To avoid the heartbreak of having to throw away your hard-earned milk supply, it is advisable to do a test on a sample first: 

– If you notice a change in smell after 3 or 4 days, but your baby still accepts the milk, there is no problem.

– If your baby no longer accepts the milk, you will need to heat your milk in advance. The process is simple: heat your freshly expressed milk to 50–60°C for 5 minutes, then place it in the fridge to cool rapidly before freezing. Heating destroys the lipases responsible for the change in smell.

If there is a change in taste or smell due to oxidation

Some studies show that this smell can also appear with chemical oxidation of the milk. It may be due to the presence of free copper or iron ions in the mother's drinking water, or to certain polyunsaturated fats in her diet. This is again safe for your child. 

In this case, heating the breast milk will not help. To avoid this soapy smell, here are the recommendations from Nancy Mohrbacher, IBCLC:

– Avoid drinking tap water and switch to bottled water for a while,

– Avoid foods in your diet such as anchovies, which contain rancid fats,

– Stop taking fish oil supplements.

Another specialist, Nicola Singletary, PhD MAT, IBCLC, makes the following recommendations:

– Freeze immediately without prior time in the fridge,

– Store milk for no more than 3 days in the fridge,

– Store milk for no more than one month in the freezer.

The ideal container remains the breast itself, but if you need to express milk for your baby, the choice of container will depend on the storage method and duration you have chosen.

For several years now, different schools of thought have been debating which is the best material for storing breast milk — glass or plastic containers.

– For deep-freezing, BPA-free breast milk storage bags appear to be a good choice, as does glass (tinted if possible),

– For other storage methods, white blood cell preservation appears to be better when using a plastic bag. If you opt for plastic containers, make sure they are also BPA-free.

In all cases, thorough washing of the container beforehand is essential, and you must also ensure that the lid seals hermetically. 

Direct breastfeeding, with freshly expressed breast milk, is preferable to refrigerated milk in terms of health benefits. Indeed, it has more effective antibacterial properties and is the richest in vitamins, antioxidants and lipids.

Simply refrigerated milk is also preferable to frozen milk. Freezing destroys some of the anti-infective factors in milk.

But of course, breast milk will always be better for your baby than infant formula, regardless of how it is stored.

We tell you more about expressing milk in our article "How to express your milk”.

Is it normal for my milk to separate into two layers?

Yes, after refrigeration or freezing, milk separates into a "watery phase" and a "creamy layer".

Can you shake breast milk?

You can mix it, but avoid shaking it too vigorously (like a cocktail). Ideally, use a gentle swirling motion to combine it. Common sense goes a long way! And your milk will always be wonderful, even if it's been shaken a little too much.

Can you use a microwave?

To warm frozen breast milk, you can use a warm bain-marie or a suitable bottle warmer, but never a microwave, which can not only reduce the quality of the milk but also — and more importantly — cause burns. Shake the bottle well before checking the temperature. 

Can you refreeze milk?

Never refreeze thawed milk. If the milk has been warmed, it must be consumed within one hour.

What if I have exceeded the use-by date?

Above all, don't throw the milk away — you can add it to your baby's bath or use it to make soap.

As long as simple hygiene rules and precautions are followed, it is easy to store milk in the fridge or freezer, and this can offer many benefits for continuing breastfeeding and maintaining milk supply. To support your milk supply, you can also take a breastfeeding supplement. 

You go mama!