How to safely store formula milk: a complete guide

If you choose to formula-feed your baby (whether exclusively or in combination with breastfeeding), you’ll know that there’s a whole new world of things that you need to know. As well as the different types of baby formula, bottle-feeding equipment and how to sterilise it, you’ll also need to get to grips with how to store formula milk to help keep your baby safe from germs.

Formula milk storage guidelines might seem complicated at first, with so many dos and don’ts to follow. That’s why we’ve created our handy guide (including guidance from the Healthcare professional) to formula milk storage, with expert tips on everything from preparing a feed to storing formula in the fridge and feeding on the go.

Before we jump straight into formula storage,  a reminder on how to safely prepare your baby’s bottle¹.

1. Wash your hands and the surface you’ll use.
2. Boil at least 1l of fresh tap water (you can do this in the kettle).
3. Leave the boiled water to cool for no more than 30 minutes so that it reaches the recommended temperature.
4. Follow the manufacturer’s instructions for the amount of water and number of scoops of formula you need.
5. Screw the teat and retaining ring onto the bottle and pop the lid on.
6. Shake the bottle until the formula powder dissolves.
7. Cool the formula to a safe temperature by holding the bottle (with the lid on) under cool running water.
8. Test the temperature of the formula on the inside of your wrist – it should be around body temperature.

The safest way to formula-feed your baby is to make up a fresh bottle for every feed and give it to your baby as soon as they’re ready and it’s cool enough. This is because bacteria thrive in warm, wet environments like your baby’s bottle if left for too long at room temperature².

Having said that, sometimes you’ll need to find storage for formula milk, and it’s important to do this in the safest way possible.

Don’t worry, though – our three golden rules make infant formula storage safe and simple.

Do not store formula at room temperature for any longer than 2 hours³.

If you make up a bottle but don’t use the formula straight away (for example, if your baby opted for a snooze instead), you can leave it out at room temperature for a maximum of 2 hours. Any longer, and there’s a chance that bacteria could grow and make your baby poorly. 

After 2 hours, it’s safest to throw the leftover formula away and make up a new bottle when you need it³.

Once your baby has started a feed, use or discard the formula from that bottle within 1 hour⁴.

That’s because your baby’s saliva can mix with the formula milk and cause bacteria to grow if the feed is left at room temperature for any longer than an hour.

You can store formula in the fridge for up to 24 hours².

NHS guidance states that you should make your baby’s bottle as and when you need to. However, on the odd occasion, it may be that you can’t follow this advice (for example, if you’re travelling). If you have to make a bottle ahead of time, when it comes to storage, formula milk can be prepared, cooled, and popped in the fridge. Store the bottles at the back and double-check that your fridge is set to 5℃ or below to help prevent bacteria from growing².

If you don’t use the formula in your fridge within 24 hours, you’ll need to throw it away.

It might help to use labels or set a reminder on your phone, so that you don’t forget when you made up the bottles (you’ll have a lot of other things on your mind with a new baby on your hands!).

From powdered formula to ready-to-feed, let’s take a look at the formula storage guidance for each, so you know what to do whichever you choose.  

A cool, dry place, like your kitchen cupboard, is the perfect place to store tubs of powdered formula. Be sure to shut the lid tightly after each use to help keep the powder fresh and throw any remaining powdered formula away within 4 weeks (always check the expiry date, too).

Here’s a top tip from Sylvie’s mum: ‘I used to write the date I opened the pack on the lid. Especially when my baby got older and was drinking less formula as she ate more solid food. Writing the date helped me keep track of when I opened the pack, and whether or not it was still safe to use.’  

Unopened powdered formula must be used before the expiry date. 

When it comes to ready-to-feed formula, storage after opening, as well as unopened, is an important consideration.

Unopened ready-to-feed formula milk can be stored in a cool, dry place rather than the fridge, but always check the instructions on the bottle to be on the safe side.

When you’re ready to use the formula, shake and pour the amount you need into a sterilised bottle and then throw away anything that your baby doesn’t finish from the bottle.

In terms of ready-to-feed formula storage after opening, you can keep anything left in the carton or bottle in the fridge (which might be the case if you’re buying bigger cartons or bottles rather than smaller individual ones). It will need to be stored upright, with the lid firmly on, and be used within 24 hours. Again, always follow the manufacturer’s instructions to be sure.

To warm up a bottle that’s been in the fridge, follow these steps²:

1. Take the bottle out of the fridge just before you need it (don’t let it come to room temperature).
2. Pop the bottle in a bowl of warm water. Make sure the water level doesn’t come above the neck of the bottle.
3. Leave the bottle in the water for up to 15 minutes.
4. Check that the milk is at the right temperature by dropping a little on the inside of your wrist. It should feel lukewarm – not hot or cold.
5. Feed your baby immediately. 

You may choose to use a bottle warmer if you have one. In that case, check the manufacturer’s instructions to help you use your bottle warmer safely.

Sometimes, you’ll need to feed your baby when you’re out and about. If that’s the case, you could pack a bottle of ready-to-feed liquid formula and a sterilised bottle. Just be sure to follow the instructions on the bottle or carton when feeding your baby³.

If you choose to use powdered formula, here’s what you’ll need to do for safe formula storage on the go.

Take a measured amount of formula powder, a vacuum flask of just-boiled water, and an empty sterilised feeding bottle with you so you can prepare the formula as usual when your baby needs it³. If the flask is full and properly sealed, the water will stay at the recommended temperature (above 70 degrees) for several hours.

Most airlines allow you to travel with enough formula milk for the journey. However, it’s always best to check before you go. In addition, it’s a good idea to arrive at the airport ahead of time, to ensure that you can get through security with time to spare - nobody likes a last-minute dash through the airport!

Some airports have pharmacies that will allow you to pre-order the formula milk that you need for your journey and holiday, which can be very helpful.

If your baby is hungry, feeding them during take off and landing can actually help, as the sucking reflex can help your baby’s little ears adjust to any pressure changes.