Preparing a baby bottle on the go is safe on one condition: never carry a bottle of made-up formula at room temperature. The simplest rule, set out by Anses, the French food safety agency, is to carry the water in the bottle and the powder in a separate container, then mix them at the last moment. Everything else, whether a formula dispenser, a flask, an insulated bag or liquid formula, simply makes this easier depending on how long you are out.
This guide sets out what French and international official guidance says, then compares the three possible ways to organise it. It is written for parents giving powdered infant formula, alongside breastfeeding or instead of it.
Why a made-up bottle should not be carried warm
Powdered formula is not sterile. Anses points out that it may contain a very small number of micro-organisms, which multiply over time as soon as the powder is mixed with water. Health Canada names the most closely monitored bacterium, Cronobacter, which causes rare but serious infections in babies.
Warmth speeds up this growth. A made-up bottle kept warm in a bag, or held lukewarm in an insulated bottle during an hour-long journey, creates exactly the conditions that health agencies ask parents to avoid. That is why making up the feed just before it is given is the standard, at home and when out and about.
Baby bottle on the go: how long can you keep it?
In France, Anses sets a limit of one hour at room temperature, including preparation time, away from sunlight and any source of heat. A bottle that has been started and is not finished within the hour should be thrown away. The time limits do not add up: one hour of travel followed by one hour of feeding is not allowed.
International guidance is a little more generous. The 2007 WHO/FAO guidelines and Health Canada allow two hours from the start of the feed, after which any leftovers are thrown away. The difference comes from each body's assumptions about the temperature of the water used. In practice, sticking to the French one-hour limit keeps the whole family on the safe side.
A bottle made up in advance and kept cold follows a different logic. Storage in the fridge, its limits and the question of water abroad are covered in our article on which water to use for baby bottles.
Water and powder kept apart: the standard method
The Anses fact sheet is clear: carry the water in the bottle and the powder in a separate container, then add the powder at the last moment and mix well. This method works for a two-hour outing as well as for a whole day, since nothing is made up before the feed.
The formula dispenser
A formula dispenser is a small container with compartments, often three or four, each holding the powder for one bottle. It saves you carrying the whole tin of formula and handling the scoop outdoors with hands that are not always clean. Anses asks that the scoop stays dry and is the one supplied with the original tin: measuring the portions at home with that scoop meets this requirement.
Two details matter when choosing one. The lid must close firmly so the powder does not spill into your bag. The compartments must be easy to wash and dry completely, as damp powder spoils. The WHO/FAO document refers to a clean, disinfected container for the powder portions: failing that, a thorough wash in hot soapy water and air drying are the minimum.
The water in the bottle
Pour the water at home into a clean bottle, in the exact quantity stated by the manufacturer. Tap water is suitable in France under normal conditions, and bottled water must be labelled as suitable for infants. An opened bottle of water should be kept in the fridge and used quickly, within 24 hours according to Anses.
A bottle filled with water can wait several hours in your bag without any particular health risk: it does not contain any milk yet. The quantities, however, are checked when you make up the feed, following the proportions on the tin exactly.
Do you need a flask of hot water for the bottle?
There are two different uses. The first is to carry hot water so you can make lukewarm milk without a bottle warmer. The second, recommended by the WHO for some babies, is to make up the bottle with water at 70 °C or above to kill any bacteria that may be in the powder.
Health Canada reserves this 70 °C method for babies under two months who were born prematurely, are immunocompromised or had a low birth weight. For a healthy, full-term baby, water at room temperature is enough. The French Anses recommendations do not adopt the 70 °C method for the general population and focus instead on making up the feed just before it is given.
If you take a flask, take practical precautions. Very hot water must be cooled before the feed, under cold running water or by waiting, then tested on the inside of your wrist. The WHO/FAO document states that the water must be used within 30 minutes of boiling to stay above 70 °C: after that, it no longer acts on bacteria, but it can still be used as warm water for a healthy baby. A wide-necked flask and a bottle with easy-to-read markings help avoid measuring mistakes.
Liquid infant formula: the simplest option for long journeys
Ready-to-feed liquid formula, sold in cartons or small bottles, is sterile as long as the packaging is sealed. Anses points this out, and the WHO considers it the safest option when no boiled water is available. It travels at room temperature, is opened at feeding time and is poured straight into the bottle.
Its drawbacks are the price, noticeably higher than powder, and the pack sizes, which rarely suit the small feeds of the first few weeks. Once a carton is open, the rest is kept closed in the fridge for as long as the manufacturer states. For a journey of several hours, a night train or a day with no access to a kitchen, it is often the most comfortable compromise.
What about a bottle made up at home and carried cold?
This option exists in the guidance, with strict rules. WHO/FAO allow bottles made up in advance to be transported if they have been cooled quickly, refrigerated at 5 °C or below, then placed in an insulated bag with ice packs just before leaving. On arrival, they go back in the fridge or are warmed for immediate use. If the bottles cannot be kept cold for more than two hours, the WHO asks parents to switch to making up feeds at feeding time.
Anses is stricter: cold transport must not exceed one hour, and the bottle must be put back at 4 °C as soon as you arrive. This option therefore suits a short trip to nursery or to a childminder, not a day out. Warm the bottle in a bain-marie or a bottle warmer, never in the microwave, and give warmed milk within 30 minutes according to Anses.
Which approach for which length of outing?
- Under two hours, in town: water in the bottle, one portion of powder in the formula dispenser. The feed is made up on the spot, at room temperature.
- A whole day out: as many bottles of water as feeds, or a bottle of water suitable for infants to open on the spot, plus the portions in the formula dispenser. A flask of hot water if your baby refuses cold milk.
- Long journey by train or car: liquid formula for simplicity, or water and powder kept apart. Our tips for travelling by train with a baby and for a long car journey cover breaks and timings.
- Dropping off at the childminder’s: powder and water kept apart, or a made-up bottle carried cold for less than an hour, labelled with the child’s name as Anses requires for childcare settings.
- Staying abroad: if the tap water is not safe, use boiled and cooled water, or liquid formula. First trips are covered in our article on travelling with a baby.
The kit that really matters
Three items are enough in most cases: a formula dispenser that closes properly, one or two extra bottles for water, and an insulated bag if you are carrying cold milk. Add a flask if your child will not accept milk at room temperature. Everything else, from travel bottle warmers to portable formula makers and compartment bottles, is about comfort, not safety.
The teat does not change when you are out. If your baby drinks faster or splutters outdoors, it is often the position or the distractions, not the kit: our guide to baby bottle teat flow helps you tell the difference. Back home, wash the bottle and the formula dispenser in hot soapy water, then leave them to air dry, without a tea towel. Sterilising is not necessary at home, as explained in our article do you need to sterilise baby bottles.
Common mistakes
- Keeping a made-up bottle warm in your bag “for later”. This is the only real health risk of a baby bottle on the go.
- Warming the same bottle several times, or putting milk that has already been warmed back in the cold. Health Canada and Anses both rule this out.
- Using a scoop from another brand, or a kitchen spoon: proportions vary from one manufacturer to another.
- Carrying damp powder or a formula dispenser that has not dried properly.
- Relying on the microwave in a café or a motorway services: uneven heating and a risk of scalding, and both agencies advise against it.
In the first month, outings stay short and the bottle is usually made up before leaving or after getting home. Our article on first outings with a newborn helps you plan these timings. For any question about our products and their materials, the Treelys® FAQ is there for you.
Key takeaways
A baby bottle on the go is made up at feeding time, with the water in the bottle and the powder kept separately. One hour at room temperature in France, preparation included. Liquid formula makes long journeys easier. Carrying a bottle that has already been made up is only an option if it is kept cold, for one hour according to Anses, two according to the WHO. The 70 °C flask method is reserved for vulnerable babies, not a must.
Sources
- Anses, “Biberon : comment le préparer et le conserver ?”, 17 January 2013.
- Anses (Afssa), “Recommandations d'hygiène pour la préparation et la conservation des biberons, questions/réponses”, July 2006.
- WHO/FAO, “Comment préparer un biberon de lait pour nourrissons en dehors du domicile”, 2007. Edition distributed by the Luxembourg Ministry of Health.
- Santé Canada, “Reconstitution et manipulation d'une préparation en poudre pour nourrissons”, updated 27 June 2025.
- INSPQ (Québec), guide Mieux vivre avec notre enfant, “Manipulation des préparations commerciales pour nourrissons”, updated 17 February 2026.
