Preparing Infant Formula Safely: Step-by-Step Guide for New Parents

Making up a bottle is something you'll do dozens of times a week — and once you have a rhythm, it becomes second nature. Whether formula is your primary feeding method or you're supplementing alongside breastfeeding, the same careful steps apply. This guide follows the approach recommended by the WHO, NHS, and CDC, including the small details that tend to matter most when you're tired and doing it at 3 AM.

If you're still deciding which formula type to use, your health visitor or midwife is the right first stop — that's a separate question, and this guide covers preparation.

Why the Water Temperature Matters

Powdered infant formula is not a sterile product. Even when sealed, the powder can occasionally contain small amounts of bacteria — most notably Cronobacter sakazakii or Salmonella. These are rare but can cause serious illness in young infants.

Mixing the powder with water that has been heated to around 70 °C (158 °F) kills those bacteria in the bottle. That is the single most important reason the instructions say "hot water first, then cool": cooler water is more convenient, but it does not give your baby the same protection.

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. Never substitute a scoop from a different brand
• Boil fresh water only — don't re-boil water that has already been boiled and don't use water that has been sitting in the kettle

Step by Step

1. Boil fresh tap water in a clean kettle. Use water that has not been previously boiled.
2. Let it cool for no more than 30 minutes. The goal is water still around 70 °C when it meets the powder. A timer helps.
3. Pour the correct amount of water into the sterilised bottle first. Most formulas 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 your formula. Level off each scoop with the flat edge of a clean knife. Do not pack the powder and do not add an extra scoop for hunger.
5. Attach the ring and cap and shake well until the powder is fully dissolved.
6. Cool the bottle quickly — hold it under cold running water, or stand 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 full process takes around 5 minutes once you have a routine.

Making Nighttime Feeds Easier

At 3 AM, five minutes can feel like a long time. These approaches keep the safety steps intact while reducing the effort:

Option 1 — Flask method: Keep a vacuum flask of freshly boiled water beside your feeding spot before you go to bed. Water in a good vacuum flask stays hot enough to use for approximately 30 minutes after pouring. Add pre-measured powder from a clean dispenser, shake, and cool briefly.

Option 2 — Fridge bottle: Prepare a bottle before bed using the full step-by-step above, cool it rapidly, and refrigerate immediately. When the feed is needed, warm it in a jug of hot water — never a microwave. Fridge-cold prepared formula is safe for up to 24 hours.

Option 3 — Powder dispenser: Pre-measure formula powder into a clean, dry dispenser before bed. You still need water at the right temperature, but measuring powder at 3 AM is one less step.

None of these are shortcuts that bypass the 70 °C rule — they are ways to reduce preparation time while keeping the safety steps in place.

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 can be much hotter than the wrist-test reads.
• Do not re-use leftover milk from a bottle your baby has already drunk from. Saliva introduces bacteria that multiply quickly at room temperature.
• Do not use flavoured, sparkling, or mineral-rich water — stick to still, low-mineral water.
• Do not re-boil water — reboiling concentrates minerals beyond safe levels for infants.

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 of opening |

When in doubt, make a fresh bottle rather than reusing one you are uncertain about.

When You're Out and About

Formula preparation away from home is manageable with a little planning:

• Carry pre-measured powder in a clean, dry dispenser and a vacuum flask of hot water (freshly boiled before you leave). Mix when you arrive. Check the temperature before adding powder.
• Carry a fridge-cooled, made-up bottle in an insulated bag with an ice pack. Use within 4 hours of removing from the fridge, or within 2 hours once warmed.
• Ready-to-feed (RTF) liquid formula is sterile and requires no preparation — ideal for day trips, air travel, or emergencies. It costs more, but on difficult days it simplifies things considerably.

Special Cases

Some babies need extra care when feeds are prepared:

• Under 2 months
• Born prematurely or with low birth weight
• With immune system conditions

For these babies, use freshly boiled water at 70 °C for each feed and prepare bottles fresh rather than in advance. Follow any specific guidance from your neonatal care team or paediatrician — their recommendations are often stricter than the standard guidelines above.

When to Ask for Help

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

• The baby is regularly unsettled during or after feeds
• Feeds often end in forceful vomiting or ongoing distress
• You are unsure whether the formula type is right for your baby
• You notice possible signs of allergy or intolerance: persistent inconsolable crying, blood or mucus in stools, a rash or hives appearing alongside digestive symptoms
• The baby has any ongoing medical condition that affects feeding

Small changes in preparation technique, feeding pace, or formula type often make a real difference — and your health visitor is a good first point of contact.

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

Related Reading

• Choosing a Baby Bottle — materials, sizes, and what to look for in a bottle for formula feeding
• Paced Bottle Feeding — the technique that most closely mirrors the pace and rhythm of breastfeeding
• Bottle Nipple Flow Guide — choosing the right flow rate at each stage
• Cleaning and Sterilising Bottles — how often to sterilise, which methods work, and when it matters most
• Combination Feeding — using formula alongside breastfeeding

References and Further Reading

• NHS: How to make up a formula feed — Step-by-step NHS preparation guide including water temperature and storage times
• WHO: Safe preparation, storage and handling of powdered infant formula — World Health Organization guidelines on powdered formula preparation, the case for 70 °C water, and storage
• CDC: Cronobacter and powdered infant formula — Why 70 °C water matters and which infants are most at risk
• AAP / HealthyChildren.org: Formula Form and Function — American Academy of Pediatrics overview of formula types, preparation methods, and safe storage
• UNICEF UK Baby Friendly Initiative: Guide to infant formula for parents and carers — Comprehensive, non-promotional guide to choosing, preparing, and using infant formula safely

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