How to prepare a bottle of formula correctly

How do you prepare a formula bottle? If you are mixed feeding or exclusively bottle-feeding, there are recommendations for preparing a formula bottle, which is why our midwives have put together this post with the latest evidence-based guidance on preparing a formula bottle.

Which milk are we going to use?

It is well known that breastfeeding is the best feeding option for your baby, exclusively until 6 months and as a complement until the age of two. But there are many occasions when it is necessary or desirable to use formula as well, either in a mixed way with breastfeeding or exclusively.

These formula milks are preparations for babies that you can find in liquid form or as a powder to dilute in water, and there are two types of infant preparations. So-called first infant milk or type 1 milk, which is used for babies aged 0 to 6 months (although you can use it throughout the whole first year of life), and follow-on milks or type 2 milk, which are the ones that would be used from 6 months onwards.

Hygiene when preparing the bottle

Before starting the bottle preparation, it is important to bear in mind that the manufacture of powdered milk for infants does not guarantee its sterility, even when it is produced respecting all the hygiene standards in force. And if we add poor handling or incorrect storage to that, the risk of bacterial multiplication increases considerably.

That is why proper preparation and storage of the bottles will be a priority in order to prevent illnesses that are sometimes very serious for babies, caused by bacteria such as Cronobacter and Salmonella.

Preparing the bottle

• The recommendations for preparing a bottle given to us by AEPED are as follows:
• You must wash your hands with soap and water before preparation.
• Both the bottle and the teat must be clean and stored on suitable surfaces, or wrapped in paper, avoiding the use of kitchen cloths.
• If you offer your baby the liquid version of infant formula, you will only need to pour the amount your baby takes into the bottle and warm it.
• If you use powdered milk, bear in mind that it is not sterile, so the recommendation given to us by the European Society for Paediatric Gastroenterology, Hepatology and Nutrition is:
• Read the instructions on the powder preparation you are going to use, with which you will calculate the amount of milk and water needed.
• If you use bottled water, heat it to at least 70 °C to destroy the bacteria and do not let the water cool for more than 30 minutes before making the mixture. You can check this temperature with a thermometer.
• If you use tap water, boil this water, as we explain below.
• Add the water (at least 70 °C) to the bottle and then add the exact amount of powder, in accordance with the instructions on the label, in a proportion of one level scoop of powdered milk for every 30 ml of water.
• Check the temperature of the milk with a few drops on the inside of your wrist: it should not burn.
• After giving the bottle, discard all leftovers that have not been consumed within a maximum of 2 hours.

Things to consider when preparing a formula bottle

• Prepare the bottle for each feed, although if necessary you can prepare them for the whole day: you will simply need to keep it in the fridge.
• You must discard leftover milk after each feed.
• You can keep the water you are going to use to prepare the bottle in a hot thermos, in order to add the formula powder just before the feed, but do not keep the already prepared bottle in the thermos.

Adding the powder to the bottle

The recommendation for adding the powdered milk to the bottle is to always pour the warm water into the bottle first and then add the scoops of milk powder, level with the scoop. And how many scoops? As a general rule, you will need to add one level scoop for every 30 ml, which is also known as 1 ounce of water.

So we will have bottles of 60, 90, 120 ml, etc. And since we have poured the water in first with the amount the baby should drink, it is normal for the total level to rise after adding the powder, and that will be what should be drunk.

Although it is true that most commercial preparations already state the amounts per feed on the tin itself. These amounts are a guide and do not mean that your baby has to finish the whole feed. You should not force it, and to know whether your baby is well fed or not, what matters is how satisfied they seem and their weight gain, not how much they eat.

Warming the bottle milk

To warm the milk in the bottle, the recommendation is to place the bottle in hot water and keep stirring so that the contents of the bottle warm evenly. It can be warmed with bottle warmers and microwaves, although the latter is not recommended because it does not heat evenly, so there may be cooler parts and parts that burn. If your only option is the microwave, stir the bottle well after warming it and check that the milk does not burn by putting a couple of drops on your wrist.

Preparing bottles for nursery

And what if you have to take bottles to nursery? Well, here are the recommendations the guides give us for preparing bottles for nursery.

• It is recommended to prepare the feeds with water at no less than 70 °C and leave them to cool. It is important that the cooling happens quickly, for example by immersing the feed in cold water or by holding it under the running tap.
• Once the feeds are cold, you can transport them to nursery in cold conditions (a cool bag, for example).
• Label each of your baby's feeds so that the nursery knows which one belongs to your baby.
• At the nursery, when they receive the bottles, the staff will place them in a fridge used exclusively for this purpose.
• The temperature of the fridge will not exceed 5 °C and will be checked daily.

Boiling the water for the bottle

Another controversial topic is that of boiling the water for bottles. In the past there was a belief that you should boil the water with which we prepare a bottle. But do we really need to boil tap water in order to prepare bottles? The answer must be reasoned according to the disinfection of the tap water.

And this comes from the fact that the Maternal-Neonatal Health Guide (Guía de Salud Materno-Neonatal), a health information publication for parents that was handed out in Spanish hospitals, recommended both in its first edition of 1997 and in the current one of 19991 that the bottle should be prepared with tap water that has always been boiled (about 10 min) and lukewarm.

Although it should be borne in mind that there have recently been outbreaks of salmonellosis in babies. A very important fact that makes us reconsider the importance of a correct bottle preparation based on correct hygiene and a minimum preparation temperature of 70 °C to avoid this possible bacterial proliferation, avoiding the recklessness of warming it and leaving it for hours at room temperature.

Problems with boiling water for 10 minutes

This 10-minute boiling of tap water increases the sodium concentration about 2.5 times, so the reconstitution of first infant milks with tap water easily exceeds the upper sodium limit permitted by ESPGHAN of 1.2 mEq/100 ml, established with the aim of protecting the infant's kidneys from an excessive renal solute load.

Furthermore, water boiled for 10 min in an open container multiplies the nitrate concentration by 2.4, so that tap water with 23 mg/l of nitrates (a figure below the guide value)6 would exceed 50 mg/l (the maximum tolerable value) when boiled, which would mean an additional risk of methaemoglobinaemia.

You do not need to boil the water for bottles if it is bottled

The current recommendation is to use low-mineral natural mineral water (less than 25 mg/l of sodium) that is bottled, which by definition contains no viruses, bacteria or protozoa. But yes, prepare the bottle at a minimum temperature of 70 °C in order to avoid the proliferation of bacteria, because preparations made from powdered milk are not sterile.

And if bottled water is not used, it can be stated that 1 minute of boiling (at sea level) is enough and avoids the added risk of an excessive ionic intake, as recommended by the WHO.

How long should you use bottled water or boil water that is not bottled?

Up to what age should this recommendation be maintained? The recommendation of the annals of paediatrics is that it is probably until 9-12 months, since from that age your baby is already crawling and it seems inconsistent to boil water while being unable to prevent their dirty hands from the floor from going to their mouth.

Storage time for prepared milk

Just like breast milk, prepared milk has certain storage times, and if you are going to prepare several bottles in order to have them already prepared, remember that you must warm them at the moment of giving the feed and that this prepared milk can only be kept for 24 hours in the fridge, and if it is not used it must be thrown away.

Washing the bottle

To wash the bottle, as well as the teats, water and soap is enough, whether by hand or in the dishwasher, making sure that no traces of milk are left. And you do not need to buy a special soap, nor do you need to sterilise the bottles. This may seem shocking, because there is a widespread culture that you should sterilise them, either the first time or after every use, but the current recommendation is that it is not necessary, and we will tell you why.

For decades, the sterilisation and disinfection of bottles, teats and dummies has been a constant recommendation in paediatrics. This practice was justified years ago because the sanitary conditions of the population were extremely different: the public water supply was often not purified, refrigeration was not within reach of every budget or so perfected, and bottled waters, scarce on the market, have precise indications.

Therefore, prior disinfection or sterilisation was then fully justified in order to reduce or eliminate possible bacterial contamination. Today, the sanitary conditions in a country like ours allow us to recommend a change of attitude.

Furthermore, various studies showed some time ago that bacterial contamination was similar between washed and sterilised bottles and that the incidence of gastroenteritis did not vary.

Although you should bear in mind that sterilising the bottles is an essential step in the case of the most vulnerable babies:

• Premature babies.
• Babies with a low birth weight.
• Babies with immunodeficiency.

Recommendations for washing the bottle

Two conclusions can be drawn from the above:

The first is that, given the good sanitary conditions in our country and even knowing that Spanish legislation is the most permissive regarding the bacteriological quality of tap water, it is not acceptable for us to make parents work more than necessary by boiling water, bottles and teats for days. This effort would only be justified in some cases, when the paediatrician or the GP, who know the family and the hygienic conditions in which they live, indicate it for medical reasons.

The second is that paediatric societies and, mainly, the Spanish Association of Paediatrics, should recommend to manufacturers of artificial milks that they include washing hands beforehand when preparing first infant milks and that they remove the strict sterilisation rules from the labelling of follow-on milks.

Can I use type 1 first infant milk during the first year?

Yes, as we mentioned earlier, you can use type 1 milk throughout the whole first year. This is a controversial topic which, as we can find in Carlos González's book "Mi hijo no me come", I quote verbatim:

"In the United States, the American Academy of Pediatrics recommends giving babies who are not breastfed the same milk throughout the whole first year. The WHO also believes that follow-on milks are unnecessary."

"(…) It is not that follow-on milk is better for older babies. It is worse than first infant milk, because it is less adapted. But older babies have enough capacity to metabolise it and can tolerate it. Naturally, advertising from the dairy industry tries to turn the tables and sell follow-on milk as "enriched with proteins to cover your child's growing needs". And then it says that those proteins are not needed, that it is nonsense."

Conclusion: preparing a formula bottle

As we always tell you, every situation of every mum with her baby is unique, and adapting to your moment and needs is vital. That is why with these posts we want to give you the latest evidence to help you achieve what you need. And if you were sterilising everything, we will start saving energy and time. We will be delighted to help you with anything.