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Baby & child.

Updated: 25 May 2022

How to make formula milk

In this guide we look at how to make-up formula milk so that it's safe from harmful bacteria, and what sterilising equipment to use.
Which?Editorial team
Milk on wrist 438592

Once you’ve navigated your way through the different types and brands and selected a formula you're happy with, you’re then faced with the prospect of making it. There’s no need to worry as formula milk isn’t difficult to prepare, as long as you have a decent kettle to hand. Find out which best kettles are quiet enough not to wake a sleeping baby and check out our four top tips to help you prepare infant formula correctly:

1. Clean bottles and teats thoroughly

You should wash bottles, teats and other feeding equipment in hot, soapy water as soon as you can after using them and then rinse them with running water, after which they are ready to be sterilised.

You can sterilise by using a cold water sterilising solution, by steam sterilising (using an electric steriliser or microwave steriliser) or by boiling the equipment in water for at least 10 minutes. Always follow manufacturers' instructions on how to use and how long after sterilising your equipment stays sterile. Find the best steriliser for you with our guide to bottle sterilisers.

To minimise contamination, always wash your hands before making up a feed as a baby's immune system is not as developed as an adult's.

2. Boil your kettle

When making up a feed it's best to use boiled tap water, not bottled mineral water. This is because bottled water is not sterile and it can contain too much sodium (salt) or sulphate.

NHS guidelines state that it’s best to make up milk formula using fresh boiled water from the kettle that's reached at least 70°C and then letting the formula cool to room temperature before feeding. This is because powdered formula is not a sterile product and can contain bacteria that can be harmful - water at 70°C will kill any bacteria present and reduce the risk of illness.

The NHS recommends you only make up feeds as you need them. This is because bacteria can grow and multiply in made-up formula, even when it's kept in the fridge.

If you're on holiday where tap water is not safe, use bottled water that has sodium (Na) levels below 200mg per litre and sulphate (SO or SO4) levels below 250mg per litre, and still boil the water to sterilise it.

If you prefer, you can use cartons of ready-to feed formula which is already prepared and is sterile, however these are pricey compared with powdered formula.

3. Use the scoop

When making up a feed, follow the manufacturers' instructions on the packaging as different brands recommend different measures. Use the scoop provided to measure the correct amount of formula powder and don't be tempted to add extra powder as this can cause constipation and dehydration.

Also, don't use fewer scoops than advised as your baby will not get the nutrients they need.

Don't add sugar, cereal or anything else to your baby's bottle as this is damaging to their teeth.

4. Steer clear of the microwave

If your baby prefers their milk warm, heat a bottle of formula by running hot water over it, or place it in a bowl of warm water rather than using a microwave. Microwaves heat the milk unevenly and can create hot spots which will burn your baby’s mouth.

Check the temperature by shaking a few drops on your wrist. When it feels warm (not hot) on your wrist, it is cool enough to give to your baby.