Short answer: a formula prep machine can be a safe way to make up powdered formula, but only if the water is at least 70C when it meets the powder and the machine is kept clean. The NHS says that if you use a machine, make sure the water coming out is at least 70C when it's mixed with the formula, and stop using it if it isn't.
Not every machine does. Tommee Tippee says its Perfect Prep hot shot is always at least 70C; Baby Brezza says plainly that its Formula Pro machines don't use 70C water. And a 2023 UK study found most machines tested in parents' homes appeared to fall short, so whatever you own, check it with a food thermometer.
Why the NHS says 70C
Powdered formula isn't sterile. As the NHS puts it, even sealed tins and packets can sometimes contain bacteria, and water at 70C or more will kill them. Hence the kettle method:
- Boil at least 1 litre of fresh tap water (never reboiled), and let it cool for no more than 30 minutes, so it stays at 70C or above.
- Water in the bottle first, then the powder: loosely filled, levelled scoops, using only the scoop that comes with that formula.
- Cool the bottle under cold running water with the lid on, and test it on your wrist. It should feel warm or cool, but not hot.
- Make feeds one at a time, and throw away anything left afterwards.
What UK experts say about prep machines
The NHS doesn't name or recommend any machine; its only machine advice is that 70C check.
After the 2023 study, the Food Standards Agency's chief scientific adviser stressed checking the water is at least 70C whatever method you use, and said anyone whose machine falls short should contact the manufacturer and their local Trading Standards or Citizens Advice.
First Steps Nutrition Trust is more sceptical, saying machines often don't deliver water hot enough despite their marketing. It notes the Office for Product Safety and Standards bought machines to check them; I couldn't find any published results.
Is the Perfect Prep safe?
The Tommee Tippee PerfectPrep filters tap water, dispenses a small hot shot onto the powder, then tops up with cool filtered water. Tommee Tippee says the hot shot is always at least 70C, every machine is temperature-tested in the factory, and an independent lab has tested the feeds it makes. The Perfect Prep Pro uses the same hot shot and filter, and doses the powder too.
The doubt comes from a Swansea University-led study in which parents measured hot shots at home. Only 11 of 74 machines reached 70C, against 54 of 69 parents using a kettle, and machines averaged about 66C to the kettles' 75C. The limits matter: the thermometers weren't calibrated, no bacteria were tested, and no brands were named. Tommee Tippee says food thermometers often can't read its small hot shot accurately, and that machines returned by worried parents have always tested fine in its lab.
My take: it's a sound design, but that research is reason enough to check your own machine. Note too that the routine puts powder in before water, the reverse of the NHS method.
Perfect Prep vs Baby Brezza: the 70C difference
The Baby Brezza Formula Pro Advanced (around £250) and the smaller Formula Pro Mini (around £200) dose and mix the powder automatically, quickly and accurately. But Baby Brezza's UK site states that they don't sterilise formula with water at 70C. They use cooled, boiled water, so nothing in the process kills bacteria in the powder.
Baby Brezza is upfront about this. It says guidance differs between countries, that it designed the machine around fresh feeds, accurate measuring and keeping hands off the powder, and that not all organisations agree with its use. Fair enough for a global brand, but it isn't the NHS method, which is why these machines score low on safety in my rankings. Want automatic dosing? The Perfect Prep Pro does it and keeps the hot shot.
Side by side: PerfectPrep vs Formula Pro Advanced and Perfect Prep Pro vs Formula Pro Advanced.
Other ways to get to 70C faster
- Babymoov Milky Now (around £80, our Value Star). Babymoov says it boils a full tank to 100C, cools it to the temperature you choose and holds it for up to six hours. Set it to 70C and the powder meets properly hot water, though you cool the bottle yourself. Holding boiled water for hours isn't quite the NHS's fresh-water advice, so I'd empty and refill rather than top up. Milky Now vs PerfectPrep.
- Tommee Tippee PrepGo UV (around £50). A flask, not a machine: you add just-boiled water and powder, and it cools the feed quickly. For days out, the NHS says a full, sealed vacuum flask of just-boiled water stays above 70C for several hours.
How to check your machine's temperature
- When you're not making a feed, dispense the hot water (the hot shot, on a Perfect Prep) into a clean cup, not your baby's bottle.
- Check it straight away with a food thermometer, then pour it away. First Steps advises keeping this separate from making a bottle, as the thermometer can contaminate the water.
- Below 70C? Stop using it for formula, go back to the kettle, and contact the manufacturer and Trading Standards or Citizens Advice.
I'd do this at set-up, and again after a filter change or descale.
The habits that make or break it
- Change the filter when it's due, and use the maker's own. Tommee Tippee says ordinary jug filters aren't safe in its machines.
- Run the cleaning cycles, and descale when prompted. For the PerfectPrep, Tommee Tippee says to clean before first use, every 30 days, after a week or more unused, and after a filter change or descale.
- Add the cool water within two minutes of the hot shot. Otherwise, Tommee Tippee says, discard the feed and start again.
- Clean the Brezza funnel and its cover after every four bottles, and change the tank water daily, as Baby Brezza advises.
- Measure powder properly. Level scoops, never extra powder or water. On the Perfect Prep Pro, calibrate each feed size carefully, and redo it if you change formula.
- Check every feed on your wrist before you give it.
- Sterilise the bottles anyway. The NHS says bottles, teats and other feeding kit need washing and sterilising, and a prep machine doesn't do that. Sterilisers compared.
Is a prep machine worth it?
Yes, if you're formula feeding most feeds, you're up several times a night, and you'll genuinely keep up with filters and cleaning. I'd pick the PerfectPrep (around £110, our Gold Star), or the Milky Now if you'd rather boil the water and don't mind cooling bottles. Weighing the upgrade? See PerfectPrep vs Perfect Prep Pro.
Probably not if you're combination feeding with a bottle or two a day, your baby's feeds are still under 4oz (the Perfect Prep minimum), or you know the maintenance will slide. The kettle costs nothing extra. All the prep machines compared.
When to get help
This guide isn't medical advice. If you've any worries about feeding, talk to your midwife or health visitor. If your baby seems unwell, call your GP or NHS 111, or 999 in an emergency.