Preparing Infant Formula Safely

Making up a bottle is a small ritual you'll end up doing dozens of times a week. The process itself is simple — a few careful steps, repeated calmly. This guide walks through it the way most public health bodies recommend, with the small details that tend to trip up new parents.

Why the Water Matters

Powdered infant formula is not a sterile product. Even when sealed, the powder can occasionally contain small amounts of bacteria such as Cronobacter or Salmonella. Mixing the powder with water that has been heated to around 70 °C (158 °F) kills those bacteria in the bottle itself.

That's the single most important reason the instructions say "hot water, then cool": cooler water is convenient but does not protect the baby in the same way.

Before You Start

• Wash your hands with soap and warm water
• Clean the surface where you'll be preparing the bottle
• Use a sterilised bottle, ring, and cap (see our bottle cleaning guide)
• Check the formula tin — always use the scoop that came inside it, follow the on-tin ratio exactly, and check the use-by date

Step by Step

1. Boil fresh tap water in a clean kettle. Don't use water that has been boiled before or left sitting.
2. Let it cool for no more than 30 minutes. The goal is water that is still around 70 °C when it meets the powder.
3. Pour the correct amount of water into the bottle first. Get this by reading the on-tin instructions — most brands are one level scoop per 30 ml (1 oz), but check your tin.
4. Add the exact number of level scoops. Use the scoop that came with the formula. Level off each scoop with the flat edge of a clean knife. Don't pack the powder down; don't add extra "for hunger".
5. Attach the ring and cap and shake well until the powder is fully dissolved.
6. Cool the bottle quickly by holding it under cold running water or standing it in a jug of cold water, with the cap on so water doesn't touch the nipple.
7. Test the temperature. Shake a few drops onto the inside of your wrist. It should feel lukewarm — body temperature or just below.

The whole process takes about 5 minutes once you have a rhythm.

What to Avoid

• Do not add extra powder "to make it stronger". Too-concentrated formula strains a baby's kidneys and can dehydrate them.
• Do not add less powder "to stretch the tin". Under-concentrated formula under-feeds the baby.
• Do not microwave the bottle. Microwaves heat unevenly and the core of the milk can be much hotter than the wrist-test reads.
• Do not re-use leftover milk from a finished bottle. Saliva introduces bacteria that grow quickly at room temperature.

Storage Times at a Glance

| Situation | Safe window |

|-----------|-------------|

| Freshly made bottle at room temperature | Use within 2 hours |

| Made-up bottle in the back of the fridge | Up to 24 hours |

| Bottle warmed and offered to the baby | Use within 1 hour, then discard |

| Opened tin of powdered formula | Use within 4 weeks |

When in doubt, make a fresh bottle rather than reusing one you're unsure about.

When You're Out and About

A few options for travelling:

• Carry pre-measured powder in a clean dispenser and a thermos of freshly boiled hot water. Mix on arrival.
• Carry a cooled, made-up bottle in an insulated bag with an ice pack. Use within 4 hours.
• Ready-to-feed liquid formula is sterile and convenient for day trips, air travel, or emergencies.

Special Cases

Some babies need extra care when feeds are prepared:

• Under 2 months
• Born prematurely
• Low birth weight
• Immune system conditions

For these babies, it's especially important to use freshly boiled water at 70 °C for each feed, and to make bottles just before they're needed. Talk to your health visitor or paediatrician for personalised advice.

When to Ask for Help

Speak to a midwife, health visitor, or GP if:

• The baby is regularly unsettled shortly after feeds
• Feeds often end in forceful vomiting or ongoing distress
• You're unsure whether the brand or type of formula is the right fit
• The baby has any ongoing medical condition that affects feeding

Small changes in preparation or technique often make the difference.

Let Flaske Track the Feeds While You Prepare Them

Preparing a bottle is one part of the rhythm. Remembering what the baby has already had — and when — is the other. Flaske keeps that second part quiet and simple.

With Flaske, you can:

• Log each bottle as you finish making it, in a few taps
• See the last feed at a glance, including time and amount
• Coordinate with another caregiver through private iCloud sync
• Review the week's rhythm without keeping paper notes

Flaske uses private iCloud sync so your records stay in your own iCloud account, visible only to the caregivers you choose.

Learn more about Flaske

References and Further Reading

• NHS: How to make up a formula feed — Step-by-step NHS preparation guide
• WHO: Safe preparation, storage and handling of powdered infant formula — World Health Organization guidelines
• CDC: Cronobacter and powdered infant formula — Why 70 °C water matters

This content is for informational purposes only and does not replace professional medical advice. Consult your healthcare provider for personalised guidance.