Feeding your baby expressed breast milk

Babies can be susceptible to infections because their immune systems are still developing. Find out how to prepare expressed breast milk correctly to minimise the growth of harmful bacteria.


Before expressing

Always thoroughly wash your hands with soap and water then dry them with a clean towel before expressing breast milk. You should also check advice and guidance before you start.  

Prepare bottles and equipment

Before preparing expressed milk, make sure all bottles and feeding equipment has been cleaned – and sterilised up until your baby is 3 months old. You should also make sure the area where you'll be preparing the bottles is clean. 

Storing breast milk

Each time you express breast milk, store it in a clean plastic or glass container. The container will need to be sterilised up until your baby is 3 months old. Do not add it to breast milk you expressed earlier, especially frozen breast milk. This can cause some of the frozen milk to thaw and then refreeze, which increases the risk of bacterial growth in the milk.

Storage time for breast milk varies depending on where you keep it.

Breast milk stored: Can be stored for: Comments 
- at room temperature (less than 26 degrees Celsius) 4 hours Cover containers and keep them as cool as possible (for example, surround the closed container with a cool towel)
- in the fridge (less than 4 degrees Celsius) 48 hours Store at the back of the main body of the refrigerator
Frozen breast milk stored in:  
- a freezer box in a refrigerator 2 weeks Store milk towards the back of the freezer, where the temperature is most constant
- a separate freezer unit of a fridge-freezer 3 to 6 months 
- a stand-alone deep freezer 6 to 12 months 

Source: Food and Nutrition Guidelines for Healthy Infants and Toddlers (Aged 0-2) [Ministry of Health website ]

Thawing frozen breast milk

You can thaw frozen breast milk in the refrigerator, or else put the container into a bowl of warm water.

Warming expressed breast milk

Expressed breast milk should be warmed in a bowl of hot water. Never warm expressed breast milk in the microwave, as this destroys living cells in the milk. Follow these steps:

  1. Put the cup or bottle containing the expressed breast milk into a bowl of hot water.
  2. Once warm, shake the container to make sure the milk is evenly heated.
  3. Check the milk is at the right temperature by shaking a few drops onto the inside of your wrist. If the milk feels comfortably warm on your skin – not hot or cold – it's about the same temperature as fresh breast milk.

Make sure you:

  • use warmed expressed breast milk within 2 hours
  • throw out any milk left in the bottle after a feed
  • never reheat expressed breast milk more than once.

Storing expressed breast milk while travelling

Expressed breast milk must be kept cold when you're travelling. You can keep breast milk cold for up to 4 hours in a thermos flask.

You should:

  • first wash the thermos flask in hot soapy water and rinse with boiled water. You must also sterilise the thermos if your baby is less than 3 months old
  • use the flask for expressed breast milk only. Don't use a flask that's also used for other food or drinks.

Don't carry warm milk in the flask, as this can increase the risk of bacterial growth.

Prepare the milk as you would normally, just before using it.

Feeding babies with allergies

Take extra care when preparing expressed breast milk for infants with allergies to make sure there is no cross-contamination of potential allergens.

If your baby has allergies you should take these extra steps:

  • Prepare the expressed breast milk in a separate area, and before you prepare a feed for any other infant or child.
  • Ensure hands, utensils and the preparation area are cleaned thoroughly.
  • Ensure infants with allergies have their own individual bottles or cups.

Find out more

Who to contact

If you have questions about feeding your infant safely, email info@mpi.govt.nz.

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