Here's everything you need to know about storing and reheating breast milk:

How to store breast milk

Once you have expressed your milk, you can store it in the refrigerator or freezer in sterilized containers or special freezer bags made specifically for breast milk. It’s a good idea to leave a 2cm gap at the top of containers or bags to allow for the milk to expand in the freezer – also helping to reduce the risk of messy leaks. It’s also advisable to write the date you expressed on each container, to help you keep track of your stock, and you should always use the oldest milk first.

The length of time you can store breast milk depends on your method of storage. In general the below rules are recommended:

• Room temperature: 4-6 hours at 66-78°F (19–26°C)

• Cooler with frozen ice packs: 24 hours at 59°F (15°C)

• Refrigerator: up to 8 days at 39°F or lower (4°C)

• Freezer: up to 6 months at 4°F or lower (-18°C)

It can be difficult to know how much milk to store at first, especially as you are getting used to your baby’s feeding habits, however, here at Elvie we find mom’s normally pump around 3-4oz per sitting. These smaller quantities can be stored easily and thawed quickly and can also be combined if needed.

It is totally normal for breast milk to separate when stored in the fridge or whilst it has been frozen, or to be thin with a bluish, yellowish or even brownish color. However, if your milk has a strong rancid smell or continues to separate even when swirled – whether straight from the fridge or after thawing – it is likely it has gone off and you should not give it to your baby.

How to thaw frozen breast milk

If you have decided to freeze your breast milk after expressing, it’s important to thaw it fully and safely before giving it to your baby. The NHS recommends thawing the breast milk slowly in the refrigerator for around 24 hours before you intend to feed. However, in cases where you need to defrost the milk swiftly, there are a couple of options – either hold it under running lukewarm water or swirl it in a jug of lukewarm water.

Whilst it may be tempting to head for the microwave, most medical advice strongly recommends against that. Whilst defrosted breast milk is still good for your baby, microwaving can damage the valuable proteins in the breast milk, reducing the nutrients your baby gets from it.

Thawed breast milk can be kept in the refrigerator for up to 24 hours but it’s very important not to refreeze it.

How to reheat breast milk

If your baby is happy to drink expressed milk cold, it is perfectly safe to give it to them straight from the refrigerator, according to both the NHS and APA – and it will save you some precious time! However, many babies prefer milk at around body temperature, especially when it comes to bedtime when feeding is as much about soothing and calming them as it is about sustenance.

You can heat breast milk up in a jug or basin of warm water. Once the milk has warmed through (this may take around 20 minutes), you may want to gently stir the milk to combine the creamy top and the liquid bottom, as it’s very common for separation to occur during the refrigeration and reheating process. As with thawing, steer clear of the microwave as this can dramatically reduce the nutritional value of your breast milk. It can also cause “hot spots” which can burn your baby’s mouth.

You are aiming for body temperature when reheating milk, so the best way to test it is to place a few drops on your wrist and see how it feels to you. If it feels hot on your wrist, it would definitely be too hot for your baby's sensitive tongue and gums, so you should leave the bottle to cool before starting the feed.

If during feeding your baby is unable to finish the bottle, you can keep this milk for around 1-2 hours. After two hours have passed, it’s recommended by the Academy of Breastfeeding Medicine to discard the rest of the milk to avoid bacteria being passed between the baby’s mouth and the bottle.

For further support and advice on storing your breast milk, never hesitate to reach out to your healthcare visitor or lactation consultant or visit one of the websites listed below:

UK: NHS Pregnancy and baby guide: Breastfeeding help and support

US: La Leche League USA