Breast Milk Lipase: The Reason Your Breast Milk Tastes Metallic

All the answers you need if your breast milk tastes or smells strange.

After you have gotten into your groove with pumping milk, you may notice that your breast milk smells or tastes funny.  Maybe baby is refusing to drink it, you catch a whiff of it, or you lick a drop off your finger.  It may have a metallic or soapy taste or smell to it.  Do not panic and absolutely do not dump out the milk.  Nothing is wrong with it!  In all likelihood, you are simply experiencing high lipase activity in your breast milk.  High breast milk lipase activity is a very common issue that many pumping moms face.  There is a solution, so read on to understand what exactly it is and what to do about it.

Related article: The Complete Guide on How to Pump Breast Milk

What is breast milk lipase?

­­Breast milk lipase is an enzyme that helps your baby break down and absorb the essential fat-soluble nutrients and fatty acids contained in your breast milk.  Accordingly, lipase is present in every mother’s breast milk.  The metallic or soapy taste problem occurs after breast milk is pumped from the breast and stored in the refrigerator or freezer. 

Related article: The Top 5 Best Bottles for Breastfed Babies

There are a few thoughts surrounding what causes this change in breast milk taste to occur.  Several studies (study a, study b) have been done over the years to fully understand why breast milk changes taste, but the exact mechanisms that cause this phenomenon are not fully understood.  The largely accepted reason is that breast milk lipase activity, i.e. the breakdown of fats, is higher in some mothers than in others.  This excess lipase activity is what leads to an unfavorable change in breast milk taste and/or smell.

It is important to note here that this does not mean some moms have higher amounts of lipase in their breast milk.  Rather, they simply have higher lipase activity.  This has no impact on the nutritious benefits or composition of breast milk.  When stored properly, pumped breast milk retains the same nutrient profile (including fatty acids, active lipases, macronutrient content, and bacterial load) as fresh milk from the breast when used within the CDC recommended 96 hour (or 4 day) time period.  The increased breast milk lipase activity simply means fats are broken down quicker in some mom’s breast milk compared to others.

Related article: How to Store Breast Milk After Pumping

How do you test for high lipase in breast milk?

If you are unsure if you have high lipase in your breast milk, you can perform a taste test.  Place a few ounces of freshly pumped breast milk in the refrigerator.  Check the smell and/or taste of the breast milk every hour until you notice a change.  Perform this test 2-3 times or until you consistently notice your breast milk changing at a specific time interval.  Since every mom’s milk is different, you may notice that the smell or taste of your breast milk changes in 1 hour, 12 hours, or 24 hours. 

Related article: How Does Breast Milk Smell? Sweet! Find Out More Here.

Keep in mind that some babies will drink breast milk even if it tastes metallic or soapy with no problem.  If your baby will drink it then great!  You do not need to do anything more than rest in the assurance that your breast milk is completely fine, if a bit smelly.  Millions of moms have experienced the very same issue.

However, if you perform a taste test and confirm that you have high breast milk lipase activity and your baby refuses to drink it, do not fret.  Once you know how long you have until your breast milk changes taste, you will know how long you have to inactivate the lipase activity in your breast milk by scalding it. 

Related article: Supplementing with Formula: Advice from Experienced Moms

How do you reduce the lipase in breast milk?

Unfortunately, you cannot reduce the lipase activity in your breast milk.  Again, lipase is a vital and essential component of breast milk.  Dietary changes and the foods you eat likely will not affect the amount of lipase activity in your breast milk.  With that said, you can neutralize the lipase by scalding freshly pumped breast milk.  By inactivating the lipase, your breast milk will not change taste or smell.

Related article: Determining Your Correct Flange Size (so Pumping Doesn’t Hurt!)

In order to inactivate lipase in your pumped milk and prevent it from changing taste, you need to scald your breast milk.  Scalding breast milk will cause it to slightly lose some of its nutritional value and marginally alter its beneficial properties.  However, the change to your milk is not significant enough to cause any issues, assuming your baby is nursing at the breast regularly and/or getting freshly pumped milk interspersed with heat-treated milk.  There are a few methods you can use to scald breast milk.

How to scald breast milk on the stove

  1. Place breast milk in a sauce pan and slowly heat until you see little bubbles form around the edges of the pan (around 180°F if you want to test with a candy thermometer), stirring occasionally to prevent a milk film from forming.  Do NOT let it come to a boil. 
  2. After bubbles form or it reaches 180°F, use a funnel and pour the milk into a container that is safe for hot liquids (ex. non-insulated stainless steel sippy bottle) and refrigerate for at least 30 minutes.
  3. Once the milk is cool, pour into baby’s bottles or breast milk storage bags and handle like normal (4 days in the refrigerator or 12 months in freezer).

We have an article on how to do this with pictures here: How to Scald Breast Milk Quickly & Properly.

How to scald breast milk in a bottle warmer

If you only have a few hours before your breast milk turns metallic or soapy and you are at work and do not have access to a pan and stove, you can use a bottle warmer to scald breast milk.  You will need a few supplies to do this:

  1. Bottle warmer without an auto shut off feature such as the Philips Avent Fast Baby Bottle Warmer
  2. Candy Thermometer
  3. Non-insulated stainless steel bottle such as the Klean Kanteen Stainless Steel Sippy Bottle
  4. Collapsible container + ice + water

Steps for scalding breast milk in a bottle warmer:

  1. After you pump, pour your pumped breast milk into a stainless steel bottle and place in the bottle warmer. 
  2. Fill the bottle warmer up with warm water to the same level as your bottle. 
  3. Place the thermometer into the bottle and turn on the bottle warmer.  Allow the breast milk to come to 180°F, stirring occasionally with the thermometer to prevent a milk film from forming.
  4. Once the breast milk reaches 180°F, remove the stainless steel bottle and place it into the container with ice water.  Put the cap on the bottle and place it in the refrigerator for at least 30 minutes to cool down.
  5. Once the milk is cool, pour into bottles or breast milk storage bags and handle like normal (4 days in the refrigerator or 12 months in freezer).

If you are planning to do this at work, these steps may seem a bit overwhelming at first.  However once you get the hang of it, it should only take a few minutes of active hands-on time.  Our moms that scald milk at work say it adds on about 5 minutes to their total pump session.

Related article: The Complete Guide on How to Pump at Work

What do you do with a freezer stash of frozen milk that hasn’t been scalded?

If you have been diligently creating a stockpile of milk in your freezer and you suddenly realize that you have high breast milk lipase activity, breathe!  Your 100s of ounces of breast milk do not need to go to waste.  As always, there are a few options on what you can do with it:

  1. Mix milk from your frozen stash with freshly scalded milk for your baby’s bottles.  If your baby takes 3 ounce bottles, try 1 ounce of older frozen milk with 2 ounces of freshly scalded milk.  You can try different ratios to see what your baby prefers.
  2. Mix a drop or two of alcohol free vanilla extract into a bottle of the older, non-scalded milk.  This will alter the taste to a slightly sweeter flavor.  Most babies will then take the older milk just fine.
  3. Use the older breast milk for a milk bath.  Pour 1-2 bags into your baby’s bath water.  Breast milk baths can be moisturizing to baby’s skin, help with diaper rash, and help sooth bug bites and other skin abrasions.
  4. Donate your breast milk.  If baby is absolutely refusing to take any of your old breast milk, consider donating your breast milk to a mother in need or a local hospital. Look up your local Eats on Feets chapter, check out the Human Milk 4 Human Babies Facebook page, see if there is local milk bank in your area that accepts donations, or reach out to your local hospital to see if they accept donor milk for babies in the NICU.

Related article: Strawberry Breast Milk: 6 Causes of Blood In Your Breast Milk

Are there other reasons breast milk may smell sour?

If you have tried scalding breast milk and your milk still smells strange, you may not have high breast milk lipase activity.  There are a few other reasons that may make your breast milk smell sour:

Storage container and conditions

If you clean your breast milk bottles in the dishwasher, try washing them by hand with soap and water and allow them to air dry instead.  If you are storing breast milk in plastic containers, make sure the plastic is food grade polypropylene or polybutylene.  Alternatively, try storing your breast milk in glass bottles or containers (some moms like storing breast milk in Mason jars).

If you store breast milk in plastic bags, make sure you are using plastic bags specifically designed for breast milk such as Lansinoh Breastmilk Storage Bags.  Bottle liners or other types of plastic bags do not preserve breast milk nutrients as well as bags explicitly designed for breast milk.

Related article: The Best Breast Milk Storage Bags on the Market Today

Also make sure that your breast milk storage bags are sealed tightly and placed in the back of your freezer.  Breast milk stored in bags that are not sealed completely can absorb odors from food and other things stored in your freezer.  Furthermore, do not store breast milk in the door of a freezer since the temperature can fluctuate greatly as the freezer door is frequently opened and closed.  This can lead to continual thawing and refreezing of your breast milk which is not recommended.

Finally, make sure you serve thawed breast milk as soon as possible.  The CDC recommends serving thawed breast milk within 24 hours and never refreezing breast milk.

Related article: How to Store Breast Milk After Pumping

Chemical oxidation

If scalding your breast milk does not improve the taste or smell of your milk or even makes it worse, you may be experiencing chemical oxidation instead of high breast milk lipase activity.  Chemical oxidation causes breast milk to smell or taste more sour and vomit-like rather than metallic or soapy.  The reasons that this can occur vary and can oftentimes be fixed.

  1. It could be due to a high intake of polyunsaturated fats in your diet.  If you take a fish or flax oil supplement, consume anchovies on a regular basis, regularly use old vegetable oils that may have gone rancid, or eat certain kinds of nuts such as Brazil nuts, it may be affecting the taste of your breast milk.  Try removing these from your diet and see if the issue resolves.
  2. Your drinking water may contain higher than normal levels of iron or copper ions.  If you have hard water and suspect this may be the case, change the source of your drinking water to bottled water for a period of time to see if the issue resolves.
  3. Increase the amount of antioxidants you consume, specifically beta carotene and vitamin E, and make sure you are still taking a prenatal multivitamin.

If you believe your breast milk may have undergone chemical oxidation and your baby will not drink it, try the steps outlined above in the “What do you do with a freezer stash of frozen milk that hasn’t been scalded?” section.

Related article: One Breast Producing Less Milk Than The Other? Mine, Too!

Finally, if your breast milk smells rancid and has a very distinct and “off” smell, discard it immediately.  When breast milk spoils, there is absolutely no question as to if the breast milk is safe for your baby to consume.  You will know that it is not even if you have never smelled soured milk before.  Scalding this breast milk will only make the issue worse.  Trying to combine it with fresh milk or masking the taste in another way will only spoil the good milk or upset baby’s stomach.  This is the one and only time we will ever say to dump out breast milk.  The good thing is this usually only occurs when breast milk has not been handled properly (i.e. you forget to put it in the refrigerator…we’ve all been there!).

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Shannon founded Work Breastfeed Mom in 2019 during her second round of pumping at work. She was tired of googling the same pumping questions over and over again, and discouraged at the lack of websites aimed at working breastfeeding moms. So, she created one herself. Shannon lives, works, and doles out Puffs to her little people in sunny Florida. She has her MBA and works as a strategic planner for a large healthcare system. She is passionate about coffee, memoirs, paddle boarding, and skincare routines. Shannon is mom to Scarlett and Ivy, and hopes to have more babies if her career allows.