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Two ways to safely cool frozen breast milk are slowly overnight in the refrigerator, or very quickly by placing a plastic bag or bottle in a bowl of warm (not hot) water. Once dissolved, warm it slowly to body temperature by placing it in warm water or using a bottle warmer. Do not use hot water or the microwave, and do not freeze breast milk after it has thawed.
Roasting in a well-designed freezer can feel overwhelming – each bag represents time and effort at the pump. This guide walks you through thawing and reheating frozen breast milk in the right way, so nothing goes to waste and every feed is good for your baby.
How to reduce the amount of breast milk
There are two safe ways. What you choose depends on the time you have.
Method 1: Thaw in the fridge (golden standard)
Remove the frozen bag or bottle from the freezer to the fridge the night you need it. It can take up to 12 hours for it to thaw properly, so a good practice is to stir the next day’s milk every night. Thawing slowly in the fridge keeps the milk safe and warm all the time – that’s why this is the method recommended by many health experts.
Method 2: Thaw in warm water (quick method)
Need milk soon? Stand the sealed container in a bowl of warm water and swirl it gently. When the water has cooled, add a little hot water and stir the container until the milk is gone. This usually takes about 20 minutes. You can also hold the bag or bottle under running water (not hotter than 37 ° C) for five to ten minutes.
How to heat thawed breast milk
When your milk is liquid, most babies will happily take it warm or cold – there’s no need to heat it at all. If your child likes heat, do it gently:
- Warm water bath: Place the bottle in a bowl of warm water for a few minutes.
- Bottle temperature: the heater brings the milk to a constant body temperature without heating it. This is especially useful for late night meals and on the go – check out our range of bottle warmers.
- Swirl, don’t swirl: gently swirl the bottle to mix the layers of milk and heat. Vigorous shaking can damage certain components of the milk.
Test the temperature in the palm of your hand before eating – it should be warm, not hot.
A portable bottle warmer designed for breast milk warms slowly and evenly, protecting those precious nutrients. You’ll find warmers and milk coolers together in our gift packs.
Why you shouldn’t put breast milk in the microwave
Microwaves heat differently, creating hot spots that can burn your baby’s mouth even when the bottle is cold. High temperatures can also destroy the antibodies and nutrients that make breast milk so important. Hot water does the same thing. Keep it warm all the time.
How long does diluted breast milk last?
- Room temperature: use within two hours of thawing.
- In the fridge: when it is completely dissolved, keep it for 24 hours.
- Don’t wait any longer: Don’t put thawed breast milk back in the refrigerator.
- When the child eats: use within a few hours, then discard any leftovers.
The Australian Breastfeeding Association has detailed guidelines for preparing and using breast milk. To see the full picture of cooling time and refrigeration time, see our tips for storing breast milk and how long it takes to pump breast milk.
A note on the smell of condensed milk
Some condensed milk smells or tastes like soap or metal. This is usually caused by a protein called lipase that breaks down fat, and milk is still safe for most babies. If your child refuses, you can warm the fresh milk slowly before feeding the next batch to reduce the lipase activity. Storing milk in good, tightly sealed bags also helps to keep it fresh – see our guide to using a breast milk storage bag.
Frequently asked questions
How long does it take to thaw dried breast milk?
In the fridge it can take up to 12 hours, so take it out the night before. In a bowl of warm water it takes about 20 minutes, and under warm water about five or ten minutes.
Can you refreeze thawed breast milk?
No. Once breast milk is thawed, it should not be frozen. Use within 24 hours if refrigerated, or within 2 hours at room temperature.
Can you heat breast milk in the microwave?
No. Heating the water creates a hot spot that can overheat your baby and can destroy the milk’s protective properties and nutrients. Run away with a little heat with warm water or a heating bottle instead.
How do you warm breast milk without a bottle warmer?
Stand the bottle or bag in a bowl of warm water for a few minutes, or hold it under warm running water, swirling gently until it reaches body temperature. Try a few drops on your hand before eating.
Is it okay to thaw breast milk at room temperature?
It is better to avoid. Melting on the bench allows the milk to be in a warm environment where bacteria can grow. Thaw in the fridge or in warm water instead, which makes the process safer and more manageable.
Why does my condensed milk smell like soap?
This is usually caused by the enzyme lipase that breaks down fat during storage. Milk is generally still safe. If your baby won’t drink, warming fresh milk before freezing can help reduce odors later.
This article is familiar to Australian mothers and is not a substitute for advice from a midwife, lactation consultant or child health nurse. Sources: Australian Breastfeeding Association; Raising Children Network.