LivingHow to express and store breast milk

How to express and store breast milk

Expressed breast milk is the best food your baby can eat when you are not with him. So how can you store and use your milk safely?

We answer the most frequent questions about its conservation , so that it does not lose any of its magical qualities.

When to express milk?

Expressing your milk and keeping it for someone to give it to your baby when you cannot put it to the breast is a good option and frequent in breastfeeding. You can do it manually or by using a breast pump.

If you are going to return to work or have to be away from home for a few days, it is advisable to start expressing milk a few days before and store it in the freezer. But another option may be to remove it at night and store it in the refrigerator, so that the person who is going to take care of your child while you are away, can offer it to them.

And although it is true that expressed milk retains most of its benefits, it is also true that for that it has to be properly preserved and have proper hygiene to ensure that it is safe for your baby.

What is the best method to store breast milk?

Breast milk is better for your baby than formula milk; freshly expressed breast milk is preferable to refrigerated, and refrigerated is better than frozen.

According to Medela, this is because freshly expressed milk offers the best antibacterial properties and has higher levels of antioxidants, vitamins and fat than refrigerated or frozen milk.

What initial precautions must be taken?

According to the International Milk League:

  • It can be stored at home to offer it to healthy, full-term (not premature) children.

  • Hands should be washed with soap and water before expressing milk.

  • Use containers that have been washed in hot soapy water and rinsed.

  • All milk must be labeled before storage, with the amount and the date of expression and freezing. So we can defrost the oldest milk.

How long can I store it?

If you have expressed breast milk cleanly and safely, you can store it at room temperature, in the fridge or freezer, depending on when you want to use it.

These are the recommendations of the Spanish Association of Pediatrics (AEP):


At room temperature 27 – 32 degrees, from 12 to 24 hours.


  • At 15º C: it is kept 24 hours

  • At 19 – 22º C: 10 hours

  • At 25 ºC: 4 to 8 hours

  • Refrigerated between 0 and 4 ºC: from 5 to 8 days

Frozen milk

  • In a freezer within the same refrigerator: 2 weeks

  • In a freezer that is part of the refrigerator but with a separate door (combi type): 3-4 months.

  • In a separate commercial-type freezer with a constant temperature of -19º C: 6 months or more.

What type of container is best to use?

The AEP recommends always using containers intended for food use: glass, hard plastic (transparent or opaque) or soft plastic bags designed for this use.

He explains that the associations of milk banks advise using hard containers because “they cause less loss of defensive factors of the milk during storage, and close them with a hard lid.”

Soft plastic bags are practical and inexpensive, but they spill and tear more easily.

And he adds that you have to maintain these hygiene and conservation standards:

  • To maintain maximum hygiene, do not touch the inside of the container in which the milk will be stored, so that bacteria do not enter.

  • The container must be closed immediately after introducing the milk.

  • It is recommended to store small amounts of milk (60-120 ml) in each container without filling it completely, to allow the milk to expand when frozen.

Can I add more milk to a container that already has more frozen?

According to the Milk League, it is possible, but you have to cool the fresh milk in the refrigerator for at least half an hour before adding it to the frozen container, and it is less quantity than frozen milk, so that, when mixed, the fresh milk does not melt the top layer of frozen milk.

How much milk should I express?

  • It is not necessary to express all the milk that you intend to leave for the baby at once.

  • Nor is it necessary to keep separate the different amounts that are extracted throughout the day.

  • Provided that the previously expressed quantities have been kept at a temperature between 0 and 15 degrees, the mother can use the same container to store the freshly expressed milk, for a maximum period of 24 hours and then follow the storage recommendations according to the date and time of the first extraction. Namely:

    • If the previously expressed milk has been kept between 19 and 22 degrees, the total storage time should not exceed 10 hours from the first expression.

    • And if the previously expressed milk has been kept at 25 degrees, the total storage time should not exceed 6 hours from the first expression.

How to keep breast milk in the refrigerator?

  • Chill breast milk as soon as possible after expressing it.

  • Store breast milk in the coldest part of the refrigerator: at the back, on the shelf above the vegetable compartment.

  • Don’t store it on the fridge door, where the temperature is less consistent.

How to store breast milk in the freezer?

  • Freeze breast milk as soon as possible after expressing it.

  • Check that your breast milk storage containers can be used in the freezer.

  • Don’t fill bottles or bags more than three-quarters full, as breast milk expands when it freezes.

  • Store frozen breast milk in the back of the freezer, where the temperature is most constant.

  • Keep it away from the walls of self-defrosting freezers.

How to use frozen milk?

  • Don’t let it thaw at room temperature.

  • It can be defrosted in the refrigerator in about 12 hours.

  • The best method is to place the container under the stream of cold water and gradually let the water come out warmer (up to a maximum of 37º C) until the milk is defrosted and reaches room temperature.

  • It can also be defrosted by placing the container in a saucepan with warm water and then hotter, but without putting it on the fire.

  • Never thaw or heat frozen breast milk in the microwave or in boiling water. This could damage its nutritional and protective properties, and create hot spots that could burn the baby.

  • It is not necessary to heat breast milk: it is enough to bring it to room temperature, which is how it leaves our body.

Once the milk is thawed, how long do I have to consume it?

“If the milk has been frozen and thawed, it can be refrigerated for up to 24 hours for later use, although it should not be refrozen,” explains La Liga.

How do you know the amount you are going to take?

It is difficult to calculate how much milk you are going to drink, so to avoid wasting it, it is convenient to keep it in a different container from the one that the baby puts in his mouth.

Start by offering the baby small amounts in a glass, with a spoon, a syringe or a bottle) and refill as they ask for more.

In this way, you can save what the baby has not taken for the next feeding, since the thawed milk can be kept refrigerated for 24 hours, as long as it has not come into contact with the baby’s saliva.

How to make good use of stored milk?

Medela explains that “stored breast milk tends to separate into layers and the fat (cream) stays on top.”

Therefore, it is advisable to gently shake the bottle to mix the layers before feeding the baby.

And, for hygiene, you have to discard any remaining milk that remains in the glass or bottle after one or two hours from the start of the feeding: the bacteria from the child’s mouth can end up in the milk naturally.

What if it smells bad when you take it out?

You may occasionally notice that your refrigerated or thawed breast milk has a musty odor. According to the AEP, it is due to the action of an enzyme called lipase, which breaks down fats and releases fatty acids, a process that helps prevent the proliferation of harmful bacteria.

This transformation of fat helps the baby to digest the milk and is not harmful, but it can cause him to reject it because of its taste. If not, you can offer it to them, as long as you have stored it safely.

Can I extract it outside the home and keep it?

Many mothers need to express their milk at work and they are within their rights. If you have to transport your breast milk between work and your home or daycare, it is recommended that you keep it in a cooler with ice packs.

More information | Medela and La Leche League

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