Freezing Breast Milk – What You need to Know

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freezing breast milk

A major benefit to expressing is that you can store your breast milk to use anytime from a few hours right up to a year. The method of storage will depend on how long you want keep the milk for. If you will be storing the milk to be used anytime over 7 days, then we recommend freezing your breast milk.

How To Freeze Breast Milk

Current healthcare recommendations state milk can be stored in a:

  • Small freezer compartment for up to two weeks
  • Freezer (<4°C, <39°F) for 6 months
  • Deep freeze (-18°C, 0°F) for 12 months

Best Method

Ideally you should store your breast milk when it is as fresh as possible. You can express directly into a freezer suitable storage system, or decanting your breast milk after an expressing session. Allow the milk to cool down to room temperature, and then place in the freezer. Place the milk container at the back of the freezer, as far away from the door as possible. This prevents temperature fluctuations caused by opening and closing the door causing the milk to thaw and re-freeze.

In order to make sure you use the oldest milk first, adopt a date labelling system with a waterproof label and ink on the container. It is particularly important to add babies name if the milk is being stored in a shared facility such as a neonatal unit, to prevent mix ups.

Fridge to Freezer

If it is not possible to access your freezer once the milk had cooled, you can still safely freeze your milk. You can keep your breast milk at room temperature for 6 hours (4hrs if it’s a hot room). Then transfer the milk to the refrigerator for up to 8 days and then go on to freeze the milk and it will still be safe to use.

Usually we recommend using ‘oldest’ milk first; however, we recommend you use up this milk before any ‘older’ which has been fresh frozen.

Breast Milk Storage Options


breast milk sotrage bottlesStorage bottles are ideal if you’re looking to store a small amount of milk for a short period of time. We recommend ether glass or BPA free milk storage bottles to ensure no nasty chemical leak into the milk when freezing.

An advantage of bottles is that the milk can be expressed, frozen and fed to baby using the same bottle and simply changing the teat. This helps to cut down on washing up and saves money as you don’t need to buy any additional containers. A drawback of using bottles is that they take up a lot of room in your freezer. Therefore is you want to build up a large supply we suggest using a more compact container. You can also buy specialist tray like the Medela Storage Solution to keep any bottles organised in your freezer.

Breast Milk Bags

breasmilk storage bagsUnlike regular food safe bags these are specially designed sterile bags to store breast milk. They have a secure seal which ensure the bags are leak proof when in storage. We recommend these as the best storage method if you plan to on building a medium to large breast milk supply for long term use. Express the milk either directly into the bags (depending on brand) or decant, seal and store.

We love that these bags can be stored flat and take up very little space in your freezer. The bags will hold around the same as a full bottle of milk, which is more than enough for a full feed. The downside to these bags is that they are single use, so you will need to buy in bulk if you plan to keep a large supply. Remember, whatever is stored will need to be thawed, so you may defrost more milk than is needed for a feed.

If you are likely to have a lot of milk stored in your freezer, consider buying a milk storage rack. These trays keep your freezer neat and their ‘first in, first out’ system to keeps your stock rotated.

Milk Freezer Trays

breast milk freezer traysThis is the best storage option is you want to save money and hate waste. These specially designed freezer trays with lids, allow you to freeze around 1oz at a time. So simple thaw the amount you need and there should be minimal leftover milk at the end of a feed.

Simply express you milk into a bottle and decant a portion into each slot. Pop on the lid and freeze. If you want to keep a large supply, press out a portion and keep stored in a larger freezer bag and refill your tray.

We love that these trays can also be used to freeze baby food portions, when it comes time to weaning them onto solids.

FAQ about Freezing Breast Milk

Does freezing affect the milk?

You will always get most nutrients from fresh breast milk or milk expressed within the last few hours. Breast milk constantly changes to adapt to your baby’s nutritional needs (amazing right?). So keep in mind that milk expressed when baby was 3 months old will be nutritionally different from fresh milk expressed at 6 months old. Yet any frozen breast milk will always be nutritionally better for your baby than formula.

A recent study (Garcia Lara et al 2012*) found that frozen breast milk stored for longer than 3 months loses some of its fat and calorie content. This reinforces the need to use ‘oldest’ milk first when using up your frozen milk supply. If you plan to keep milk for longer than 3 months we highly recommend a deep freeze as the lower temperature will keep the nutritional properties for longer.

There have been numerous studies which have found a slight decrease in vitamins A and C from frozen breast milk. However, the decline is still within a range which will meet baby’s requirements.

How to thaw breast milk

The safest way to defrost your breast milk is to place it in a refrigerator overnight or for around 12 hrs before use. This method is the best for keeping all the essential nutrients of the milk and prevents any nasty bacterial activity.
If you need the milk quicker, you can speed up the process by running the container under water. Start with a cool temperature and gradually increase the temperature until milk is warmed.

How to warm up breast milk

Remember you must thaw your breast milk before heating. If you heat frozen milk directly you risk losing essential fats and vitamins in the milk. Some babies may drink cool milk, but most will like it to be around body temperature.

To warm the thawed milk start by decanting the milk into your feeding bottle and secure the teat and lid. Take a medium sized kitchen jug and fill with warm or hot water. Place the feeding bottle into the jug and leave for a few minutes. Every minute or so, remove the milk swirl in a tornado motion (don’t shake) and test the temperature on your hand. The perfect temperature is when the milk is neither hot nor cold.

If you are short on time you can also use an electronic bottle warmer to heat the milk. These are great for heating the milk at a constant temperature. They often have timers so you can get extras tasks done in between waiting for the milk to heat, without worrying it will overheat. Click to read our guide to finding the best baby bottle warmer.

Never heat a bottle in a microwave or directly on a stove. By doing so you create heat pockets within the container which can scald baby when feeding.

Mixing fresh and frozen breast milk

It is safe to mix freshly expressed milk with frozen breast milk, as long as the frozen breast milk is fully thawed. Ensure the fresh breast milk is cooled and then mix with the thawed milk. Swirl the milk together to get a good mix, and heat as recommended above.

Refreezing thawed breast milk

There has been very little research into how safe it is to refreeze previously thawed breast milk. As a general rule we do not recommend refreezing the milk. We also do not recommend reheating thawed milk more than once. It is safe to keep thawed milk in the refrigerator for up to 24 hours.

Does breast milk sour?

Defrosted breast milk often has a soapy smell, due to the fats separating. It’s normal for thawed milk to have a watery appearance. We recommend that the milk is safe to use unless it has been stored longer than recommended, or has a pungent smell.

Can I freeze breast milk if I have an infection?

If you have been diagnosed with a yeast infection, it is safe to give baby any frozen milk whilst still undergoing treatment. As freezing does not kill the yeast which causes thrush, then you should throw away any leftover milk which was expressed and frozen whilst the thrush was active.

If you have been diagnosed with mastitis it is ok to freeze breast milk as long as you are not taking antibiotics. It’s important to remember your breast tissue is infected, not your milk. Others moms have reported that antibiotics give their milk a really metallic taste which baby refused.

If you found this post helpful, please share with other moms who may find it useful. Remember you can leave a comment below and let us know your tips and tricks for freezing breast milk.