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The formula should be heated only once. If your baby is still not drinking from a bottle and it has been stored well in the fridge, you can take it out and warm it up once. When your baby starts to nurse, or after the bottle is warmed, any remaining milk should be thrown away rather than expressed and reheated for another feed. Reheating the same type of water multiple times gives bacteria more opportunities, and that’s the danger we’re trying to avoid.
If you’re standing on the kitchen bench at 2am wondering if a half-empty bottle is safe to reheat, this guide walks you through exactly what’s safe, what’s not, and the best way to reheat food – all based on Australian baby feeding guidelines.
Can you reheat baby formula?
Yes – but under the right circumstances, and only once. There are two different realities that parents mean when they ask this question, and they have very different answers.
Your child’s formula is not affected
If you made a bottle, cool it and store it in the back of the fridge (not the door) at 5°C or below, and your baby has a problem. no fed from it, you can heat it at once when you are ready to use it. The prepared formula is stored in the refrigerator for 24 hours. Take out what you need, reheat once, and use immediately.
Your baby’s formula has already been fed
When your baby’s mouth touches the breast, bacteria from their saliva gets into the milk. Even if the bottle is put back in the fridge, the food should be used within one hour and not reheated for another time. When in doubt, throw it out – it’s not worth upsetting the stomach.
Why you don’t have to reheat the water more than once
Warm milk is a good place for bacteria to grow. Every time cooking oil is heated and then cooled again, it spends more time in the “danger zone” between 5°C and 60°C where bacteria multiply rapidly. Reheating a second or third time increases that risk, so the advice is to reheat once and discard the rest. The NHMRC’s Baby Feeding Guidelines recommend preparing fresh foods for every meal whenever possible, as it minimizes this risk.
The safest way to heat a formula bottle
Temperature also affects frequency. Its purpose is gentle, even warm to body temperature – about 37 ° C.
- Place the bottle in warm water. Place in a bowl or bowl of warm (not hot) water for a few minutes, gently swirling to spread the heat.
- Use a bottle warmer. Dedicated heating provides a constant temperature without hot spots – more reliable than just guessing with a kettle.
- Try it before you eat it. Hold the bottle and drop a small amount into the palm of your hand. It should be warm, not hot.
Do not use a microwave. Microwaves heat differently and create hot spots that can warm your baby’s mouth and throat, even if the bottle is cold on the outside. To learn more about why, check out our guide to the bottle warmer vs microwave.
The way to warm up when you go out
Heating is also difficult away from home, where there is no fridge or clean kettle. The best way to travel is to carry pre-measured powder and a bottle of boiled water, then mix a new bottle when your baby is hungry – so that they are not heated at all. The hydration bottle keeps water at the right temperature for hours, and the portable warmer means you can bring the bottle to keep it warm in the car or at the park. Browse our complete collection of travel bottle warmers. For more information, read how long the hot formula is in the bottle.
How long does the preparation formula last?
- Freshly made, unrefrigerated: use within 2 hours; throw it away later.
- Prepared in advance and refrigerated (baby not fed): up to 24 hours in the coldest part of the refrigerator.
- Warm up: use within one hour; do not refrigerate or reheat.
- The child has eaten from it: use within an hour, and discard.
Australia’s Raising Children Network has a handy guide to creating and storing formula. For a step-by-step guide, check out our handy formula guide, and if you’re weighing equipment, our bottle warmer comparison breaks down the options.
Frequently asked questions
Can you reheat ice twice?
No. The formula should be heated only once. If the warming bottle is not being used, throw it out instead of freezing it and reheating it, as any reheating increases the chance of bacterial growth.
Can you put warm milk back in the fridge?
No. Once the formula is heated, do not put it back in the refrigerator. Use within an hour of heating, and discard any leftovers.
How long does milk fat last before it goes rancid?
Freshly prepared medicine left at room temperature should be used within two hours. When your baby feeds from a bottle, use it within an hour and then throw away the rest.
Is it okay to reheat formula in the microwave?
No. Microwaves heat differently and create hot spots that can burn your baby’s mouth. Warm bottles by placing them in warm water or using a bottle warmer instead.
Can I reuse the formula that my child has not finished?
No. Any remaining oil in the bottle that your child drinks should be thrown away within an hour. Saliva causes bacteria to multiply when milk is stored, even in the refrigerator.
What is the ideal temperature for feeding?
Body temperature – about 37 ° C. It should be warm, not hot, when you try a few drops on the inside of your hand. Frozen or frozen foods are also safe to feed your baby if they drink.
This article is for Australian parents and is not a substitute for advice from your child’s nurse or GP. If your child has special dietary or health needs, ask the doctor. Sources: NHMRC Breastfeeding Guidelines; Raising Children Network.