Feeding Your Baby

Three reasons why your baby is rejecting your frozen or stored breast milk (hint: it could be Lipase)

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Moms- you have done an amazing job pumping and storing up all that valuable breast milk! Breast milk is packed with nutrients specifically designed to line your baby’s gut lining with nutrients to protect it, leaving the lysozymes and lactoferrin to block pathogens from entering the gut at decreased rates.1  Human milk feeding is a great contribution towards your baby’s growth and development, from newborn through the first years of the baby’s life.

How long should you breastfeed?

How long you provide your baby with human milk is a decision for you and your baby.  In the world at large, moms breastfeed their baby up to an average age of 4-7 years old, in addition to other foods. In the Western world, we use hand expressing and / or a pump in addition to breastfeeding to have milk available for our baby.  The breast milk can be stored in the refrigerator for up to 7 days and in the freezer for up to a year.   

How should breastmilk smell and taste?

Breastmilk should taste slightly sweet and have almost no odor to it. It has been recommended to complete a taste and smell test of your own BM every few hours. If your milk starts to smell, use this checklist to figure out what the cause is.  

Is baby rejecting your breastmilk?

Now, to the chase. Is your sweet bundle giving you five fingers and rejecting your frozen/stored breastmilk? Perhaps you need to do a little investigating and find out if your milk is the culprit.

Here are three reasons why your baby may be rejecting your precious breast milk:

  • Things may not be squeaky clean 
  • Excess Lipase lurking around 
  • Chemical oxidation (it’s not as serious as it sounds) 

How to clean your breast pump kit and baby bottles

Check your pump equipment, sterilize your bottles and nipples, and clean the space around where you are pumping.  Human milk is considered sterile, and in the hospital, it is handled with gloves- hand hygiene and cleaning are implemented before preparing the bottle and following to decrease the risk of concerns. It’s a good idea to check your practice of keeping clean bottles and dirty bottles (and pump equipment) separate. I know as a parent who pumped for 28 months (a story for another post), you are super on it in the beginning and then, life happens and we need a friendly reminder to stick to the clean routine. I recommend using a large pot or bin for your dirty items.  I always used my Gumbo pot, it’s tall and deep and pretty and gives me happy memories when I would see it in the kitchen. Then I would tip toe into reality when I would peek inside and see 75% of it filled with dirty bottles. Some days I’m inspired to immediately clean and prepare a tasty treat for myself (ahem, and hubby), but 98% of the time, I would sigh and roll up my sleeves and get those bottles cleaned. It’s a temporary part of the parenting gig (approximately 550 days, but who’s counting!). Bottles can be washed with warm water and soap or placed on the top rack of the dishwasher. They can be dried on the rack as well or in a clean cupboard on a clean towel.  

An additional step of sanitizing is recommended by the CDC once a day for all bottles and equipment for babies that are less than 3 months of age, born prematurely or immunocompromised.2 You can boil the bottles and equipment for 5 minutes on the stove top, or you can use a steam bag in the microwave. The daily sanitizing of baby bottles is not always necessary for older babies.  

Before sanitizing, clean the bottles first with warm, soapy water.  

How to sanitize your breast pump kit and baby bottles

Steaming can be done in the microwave by taking apart the bottles and placing them (and equipment) into the steaming bag. Following the manufacturers’ directions to steam. Once steaming is complete, remove bottles and equipment from the bag, place on a clean, dry towel to dry.  

To boil the bottles and equipment, take apart the bottles and place in a large pot. 

  • Add the cleaning bottle equipment and cover all feeding supplies with water  
  • Bring the water to a boil. 
  • Boil for 5 minutes 
  • Remove with tongs and place on a clean, dry towel to dry

What is Lipase and how does it affect breast milk?

Lipase is an enzyme found in human milk that supports the breakdown of the natural fat in breastmilk and supports digestion of the fat.  Too much of a good thing, too quickly, can begin to smell soapy.  If your milk starts to smell and taste like soap or sweat (it’s also been described as stale nuts, eek!), then most likely there is an excess of lipase present.  Most babies will refuse to enjoy human milk that is high in lipase. Yup, that’s right, you’ve stored this milk months ago — because you’re organized and amazing and the babies are giving you the hand, crying or pushing away from the bottle.  I mean, it’s a reasonable response, as the milk goes from tasting and smelling sweet like yellow cake milk to tasting and/or smelling like BLEEP soap (without the use of profanity).  Who can blame them?  Mom to the rescue to inactivate the lipase!!! 

How to get rid of the soapy smell and taste in fresh breast milk

Fresh milk with a soapy taste or smell?  No wonder your baby doesn’t want to drink it. But it’s no problem that we can’t handle.

Scald immediately following expressing on the stove top (in a saucepan) or using a bottle warmer.  Heating fresh human milk to about 180 degrees Fahrenheit (82 degrees Celsius) for 5 minutes will inactivate lipase, encouraging the excess to go away from the milk. (bbbyyeee!) 

Parents, be careful, the milk is literally scalding hot!  After scalding the milk, you can refrigerate or freeze the breast milk.  Once cooled, you can offer your baby a fresh bottle, cup or a few spoonfuls of yummy sweet human milk. 

How to get rid of the soapy smell and taste in frozen breast milk

Unfortunately (we are so sorry to tell you this), there are not many options for frozen expressed breaset milk that has a soapy/rancid/sour odor. The milk can be mixed with your fresh (or recently refrigerated) and offered to your baby in hopes they will tolerate it.  

If they enjoy the mix, that’s great! If the baby continues to refuse the frozen milk due to its taste, you can discard it or donate to the human milk bank near you. The pasteurization process destroys lipase.  

The milk bank will accept frozen milk that has been frozen for 8 months or less and has not received any heat treatment.  If you know your milk is high in lipase, keep it frozen and reach out to your local milk bank facility to coordinate. 

Does your breast milk smell like metal? It could be chemical oxidation

Now, if the milk has a metallic taste, that’s vomit-like (yeah, I know – ugk!), it’s unlikely that it’s excess lipase and instead a chemical oxidation. You can usually tell it’s chemical oxidation because scalding the milk (as an option to remove excess lipase) doesn’t change the taste. I know. Sad. Face. You have to toss it. It is considered rancid. Rancid food doesn’t make you sick, but it’s less nutritious and it doesn’t taste or smell good.

It’s okay to cry over spilled milk.   

The reason for this taste could be related to an excess of polyunsaturated fats in your food choices.  More research is being completed to better understand chemical oxidation and human milk. Common polyunsaturated foods that can have a rancid smell are whole flours, seeds, oils, nuts and brown rice.

Is the food in your pantry harming your breast milk?

Check the following in your cupboard:

Confirm fish-oil or flaxseed supplements are not expired.

Smell your oils before using them, have they gone rancid?

Make sure your containers are sealed and stored in a cool dark space

Check your water source. Is there an excess of iron or copper ions in your water?

It is recommended that when infants refuse thawed milk, mothers can try to provide freshly expressed milk whenever possible or provide breastmilk frozen for less than 7 days. Future studies could explore the methods for slowing breast milk lipolysis to maintain breast milk’s fresh flavor3

This recommendation is valid, however, there needs to be an updated feeding / pumping plan to meet the needs of the baby, while accommodating the life of the parent. Partnering with your local Lactation Consultant to support you in making a plan is recommended.  Be sure to include your support team at home and don’t forget to include your sleep schedule as an important part of that plan. This can be stressful to manage, but you can get through this. 

Three deep breaths, make a call for support, snuggle with your baby and feed at the breast when possible.  

Written by Jadah Chatterjee, Nurse, International Board-Certified Lactation Consultant and Bobbie Medical Advisor.


1- Human Breast Milk and the Gastrointestinal Innate Immune System | Science Direct

2- How to Keep Your Breast Pump Kit Clean | CDC

3- Variations in the Rancid-Flavor Compounds | BMC Pediatrics

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant's pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant’s pediatrician. Never disregard professional medical advice or delay it based on the content on this page.