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    • Home  / Breastfeeding
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    How to Warm and Thaw Breast Milk Safely: An Australian Guide

    By Kelly Northey, Certified Postpartum Nutrition Professional
    Founder of Nella Vosk • 14+ years supporting families across motherhood, feeding, and early childhood wellbeing
    Editorial Policy →

    How to Warm and Thaw Breast Milk Safely: An Australian Guide

    You pumped that milk. You labelled it, you froze it, you carried it home in a cooler bag like it was liquid gold, because it is. So when it comes time to actually use it, the last thing you want is to get the thawing or warming wrong and have to tip it down the sink.

    The good news: this is one of the genuinely simple parts of breastfeeding. There are only a few rules that matter, and once you know them, it takes the second-guessing out of every bottle. Here is exactly how to do it, and the handful of things to avoid.

    This is a practical how-to within the Milk & Nourishment Flow pillar of the Nella Vosk CARE SYSTEM, and it sits alongside our Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide for Australian Mothers. It answers one focused question: how do you take stored breast milk and get it ready for your baby, safely?

    How to thaw frozen breast milk

    There are three safe ways to thaw frozen breast milk. The one you pick depends mostly on how much time you have.

    1. In the fridge (best, plan ahead)

    Move the frozen bag or bottle from the freezer to the fridge and let it thaw slowly. This is the gentlest method and the one that preserves the most. It usually takes around 12 hours, so the trick is to move tomorrow’s milk into the fridge tonight. Once fully thawed in the fridge, it keeps there for up to 24 hours.

    2. Under cool then warm running water (faster)

    If you did not plan ahead, hold the sealed bag or bottle under cool running water, then gradually warm the water until the milk is thawed and at feeding temperature. This takes several minutes and is the quick, on-the-spot method most mums reach for.

    3. In a bowl of warm water (no running tap)

    Sit the sealed container in a bowl of warm (not hot) water and swap the water as it cools. Same idea as the tap method, gentler on the water bill, and easy to do while you settle your baby.

    The fastest SAFE way to thaw: running water, from cool to warm, is the quickest method that does not damage the milk. There is no safe way to instantly thaw frozen breast milk. If you are regularly caught short, the real fix is thawing a portion in the fridge the night before so it is ready.

    How to warm breast milk

    Whether your milk is fresh from the fridge or already thawed, warming is optional. Some babies happily take milk at room temperature or even cool, and there is nothing wrong with that. But many prefer it warm, closer to body temperature, especially newborns.

    I want to say something honest here, because I remember it well. The warming mistakes almost always happen at night, when you are running on nothing. Standing at the kitchen bench at 3am, half asleep, with a crying baby, is exactly when it is easiest to reach for the microwave or turn the water too hot just to make it faster. That is not carelessness. That is exhaustion, and every breastfeeding mother knows it. So the steps below are deliberately simple, because simple is what your tired brain can actually follow in the dark.

    Warming milk from the fridge

    1. Stand the sealed bottle or bag in a bowl or jug of warm water for a few minutes, or hold it under warm running water.
    2. Swirl it gently (do not shake hard) to even out the temperature and remix any separated fat.
    3. Test it on the inside of your wrist. It should feel lukewarm, not hot. Body temperature is the goal.

    A note on bottle warmers

    An electric bottle warmer does the same job with less fuss and more consistency, which many mums find worth it, especially for night feeds. If you use one, follow its instructions and still do the wrist test every time, because warmers can create hot spots.

    Take the Free Breastfeeding Assessment

    What never to do

    • Never microwave breast milk. Microwaves heat unevenly and create hot spots that can scald your baby’s mouth, and the high heat also damages some of the beneficial components in the milk.
    • Never boil it or use boiling water. Too much heat degrades the milk. Warm water is all you need.
    • Never refreeze thawed milk. Once breast milk has thawed, it cannot go back in the freezer. Use it or lose it.
    • Do not shake vigorously. A gentle swirl remixes the fat without stressing the milk. Hard shaking is unnecessary.

    Once your milk is thawed: how long it lasts

    Timing tightens up once milk is thawed, so this part matters. As a general guide, thawed breast milk keeps in the fridge for up to 24 hours, and at room temperature for only 1 to 2 hours. Warmed milk should be used within a couple of hours and not put back in the fridge. These are general figures, and Australia’s official storage times are set out by the Australian Breastfeeding Association and Raising Children Network, which are worth keeping handy.

    For the full set of storage times across fridge, freezer, and deep freezer, see our breast milk storage guidelines for Australia, and if you are building up a supply to thaw from, our guide to building a breast milk freezer stash covers how much you actually need.

    If your thawed milk smells soapy or off

    Do not panic, and do not automatically tip it out. Some mothers have milk that is higher in an enzyme called lipase, which can give thawed milk a soapy or metallic smell. The milk is usually still safe, though some babies refuse the taste. If this sounds familiar, our guide to high lipase in breast milk explains what is happening and what you can do about it.

    What makes thawing genuinely easy: how you stored it

    Stress-free thawing starts at storage. Milk frozen flat in small portions (60 to 120ml) thaws faster and wastes less if your baby does not finish a feed, and using your oldest milk first means nothing sits in the freezer past its window. That is the thinking behind our breast milk storage range: storage built for real breastfeeding life, so what you freeze is easy to thaw well.

    At the heart of it, the Milk Keep storage system pairs a first-in, first-out freezer organiser with temperature-sensing bags that freeze flat and thaw quickly, and a fridge magnet that keeps the storage and thawing guidelines right where you need them. For everyday fridge storage and pouring straight into a bottle, the reusable breastmilk storage bags are food-grade silicone, stand upright, and seal securely so not a drop is lost.

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    Frequently asked questions

    The fastest safe way is to hold the sealed bottle or bag under warm running water, or sit it in a bowl of warm water, for a few minutes until it reaches body temperature. Swirl gently and test on your wrist. Never use a microwave or boiling water to speed it up, as both create dangerous hot spots.

    It is safer to thaw in the fridge or under running water. If milk begins thawing at room temperature, it should be used within a couple of hours and not left sitting out. For planned feeds, moving milk to the fridge the night before is the safest approach.

    Once breast milk has been warmed and offered, it is generally recommended to use it within a couple of hours and not to rewarm it repeatedly. Warming in small portions helps avoid waste. When in doubt, follow the ABA storage guidance.

    A soapy or metallic smell after thawing is usually caused by higher lipase activity in your milk, not spoilage. The milk is generally still safe, though some babies dislike the taste. Scalding fresh milk before freezing can help prevent the change in future batches.

    No. Microwaving is not safe for breast milk. It heats unevenly and creates hot spots that can burn your baby’s mouth, and the intense heat also breaks down some of the milk’s beneficial properties. Always use warm water instead.

    Next steps

    Thaw in the fridge when you can, use warm running water when you cannot, warm gently to body temperature, and never microwave or refreeze. That is genuinely all there is to it. For the full storage picture, head to our breast milk storage guidelines, or return to the Breastfeeding Nutrition & Milk Supply: Evidence-Based Guide for Australian Mothers for everything on feeding and supply.

    You have done the hard part already. This bit is easy, and now you know it.

    Kelly x
    About the author

    Written by Kelly Northey, Certified Postpartum Nutrition Professional and founder of Nella Vosk.

    With specialised training in lactation nutrition and the practical realities of pumping and stored-milk feeding, Kelly helps Australian mothers navigate the breastfeeding journey through evidence-based guidance and maternal-led product development.