Understanding High Lipase in Breast Milk and the Benefits of Freeze-Drying

Have you ever thawed stored breast milk only to discover that it smells soapy, metallic or simply different from when it was freshly expressed? If your baby happily drinks fresh breast milk but refuses milk after it has been refrigerated or frozen, you may have come across what is commonly called high lipase milk.

It can be incredibly frustrating, particularly if you have spent weeks or months building a freezer stash.

The good news is that a change in smell or taste does not automatically mean your breast milk has spoiled. Lipase is a naturally occurring enzyme in human milk that plays an important role in breaking down fats. Changes can occur after expressed breast milk is stored because enzymes and other components of human milk remain active after pumping.

Some parents notice these changes much more quickly or strongly than others, leading to the commonly used term high lipase breast milk.

In this guide, we’ll explain what high lipase milk is, why stored breast milk can smell or taste different, whether it is still safe for your baby, and the options available if your baby refuses to drink it.

What Is High Lipase Breast Milk?

Lipase is an enzyme naturally present in breast milk. Its role includes helping break down fats so they can be digested and used by your baby.

When breast milk is expressed, however, some of its naturally occurring enzymes remain active. As milk is stored, changes to the fats in the milk can influence its smell and taste.

Some mothers find these changes happen relatively quickly. Their freshly expressed milk may smell and taste completely normal, while the same milk develops a distinctly soapy, metallic or unusual flavour after refrigeration, freezing or thawing.

This is commonly referred to as high lipase milk or high lipase breast milk.

It is important to remember that lipase itself is not a contaminant or something that has accidentally entered your milk. Lipase is a normal component of human milk and contributes to the digestion of milk fats.

It is also worth noting that the term “high lipase” is commonly used by parents, but the science behind storage-related smell and taste changes is more complex. La Leche League notes that oxidation and other changes in stored human milk may also contribute to these differences. You can read more in their guide to the smell of stored human milk.

How Can You Tell If You Have High Lipase Milk?

Many mothers first discover the issue after building a freezer stash.

Your baby may happily breastfeed or drink freshly expressed milk from a bottle, but suddenly refuse previously frozen breast milk.

When you smell or taste the thawed milk yourself, you may notice that it seems very different.

Common descriptions include:

• Soapy
• Metallic
• Rancid
• Sour
• Bitter
• Unusual or “off”

The length of time before these changes become noticeable can vary.

If you suspect high lipase activity is affecting your stored milk, you can conduct a simple test with a small amount of freshly expressed milk.

Taste or smell the fresh milk, then store it as you normally would. Check it periodically after refrigeration or freezing and compare the smell or taste with the freshly expressed milk.

This can help you understand whether storage is associated with a noticeable flavour or odour change in your milk and approximately how quickly that change occurs.

Why Does Breast Milk Develop a Soapy or Metallic Taste?

The term “high lipase” is widely used by breastfeeding mothers, but the chemistry of stored human milk is more complicated than simply having too much of one enzyme.

Lipases are involved in lipolysis — the process of breaking milk fats down into components including free fatty acids. Research has demonstrated that changes to human milk fats can occur during storage and that storage temperature can influence these changes.

This can contribute to differences in the smell and taste of stored milk.

Importantly, freezing does not necessarily destroy lipase activity. Research examining human milk stored at freezer temperatures has found that lipase enzymes can retain activity during frozen storage.

That helps explain why milk that tasted perfectly normal when it entered your freezer may taste different when you eventually thaw it.

Does Freezing Stop Lipase Activity?

Not necessarily.

It is easy to assume that putting breast milk into the freezer completely stops the biological processes occurring within it, but human milk is complex.

Research has found that important milk lipases can retain activity during frozen storage. Studies have also observed changes in milk fats during storage at typical freezer temperatures.

This doesn’t mean you shouldn’t freeze breast milk. Freezing remains an established method of storing expressed breast milk when appropriate handling and storage guidelines are followed.

For current Australian guidance, see the Australian Breastfeeding Association’s expressed breast milk storage guidelines.

Freezing simply may not prevent the flavour changes some families associate with high lipase milk.

Is High Lipase Breast Milk Safe for Your Baby?

A soapy or metallic smell by itself does not necessarily mean that breast milk has spoiled.

Stored human milk can develop changes in odour and taste even when appropriate storage procedures have been followed.

If your baby accepts the milk and it has been expressed, handled and stored safely within current breast milk storage guidelines, an unusual taste associated with storage is not necessarily a reason to discard it.

However, a smell or taste change should not automatically be assumed to be caused by lipase either.

If there is any doubt about whether milk has been stored safely, whether it may have been contaminated, or whether it is suitable for your baby, seek advice from an appropriate healthcare professional rather than relying on smell alone.

High Lipase Milk vs Spoiled Breast Milk

This distinction is important.

Breast milk can smell different after storage without being spoiled, but genuine problems with milk storage or handling can also occur.

High lipase milk is generally discussed when milk:

• Smells and tastes normal when freshly expressed
• Develops a soapy, metallic or unusual taste during storage
• Has been collected hygienically
• Has remained within appropriate breast milk storage conditions
• Shows a repeatable change when fresh milk is tested against stored milk

Milk that may have been stored incorrectly, left outside recommended temperature ranges or contaminated during pumping and handling should not simply be labelled “high lipase”.

When you’re unsure, follow current breast milk storage guidance and seek professional advice.

Why Do Some Mothers Have High Lipase Milk?

There is considerable natural variation between mothers and even between different samples of milk from the same mother.

The phrase “high lipase” can make it sound as though something is wrong with your breast milk. That’s not the case.

Lipase is a normal and useful component of breast milk.

Research into stored human milk has shown that numerous factors can affect lipolysis and the characteristics of milk during storage. There isn’t a simple threshold that mothers can test at home to determine whether they officially have “high lipase levels”.

For most parents, the practical issue isn’t a laboratory measurement of lipase activity.

“My fresh milk tastes fine, my stored milk tastes different, and my baby won’t drink it.”

That’s the problem we actually need to solve.

What Can You Do With High Lipase Breast Milk?

Discovering that your baby refuses stored milk can be upsetting, particularly when you have a large freezer stash.

Before throwing anything away, there are several things worth trying.

Try the Milk With Your Baby First

Not every baby is bothered by a change in taste.

Some babies will happily drink stored milk even when a parent notices a soapy or metallic smell.

If your baby accepts it and the milk has been appropriately handled and stored, there may be no reason to change what you’re doing simply because you notice a difference in flavour.

Work Out When the Taste Changes

If your baby refuses stored milk, try testing freshly expressed milk at different intervals.

For example, compare the smell and taste:

• When freshly expressed
• After refrigeration
• After freezing and thawing

You may discover that your milk remains acceptable for a certain period before the smell or taste begins to change.

Understanding when the change occurs can help you decide how best to store and use your milk.

Mix Stored Milk With Fresh Milk

Some families find their baby is more willing to drink stored milk when it is combined with freshly expressed milk.

If you choose to combine milk, make sure you continue to follow appropriate breast milk handling and storage guidance.

The goal is simply to make the flavour more familiar to a baby who otherwise refuses the stored milk.

Consider Scalding Milk Before Storage

Scalding is frequently discussed as a way of reducing lipase activity in expressed breast milk before it is stored.

Heat can reduce the activity of milk lipases. Traditionally, mothers dealing with persistent storage-related taste changes have sometimes heated freshly expressed milk before cooling and freezing it.

There is an important trade-off, however.

Breast milk contains many heat-sensitive bioactive components, and heating milk can affect more than lipase.

If you are considering routinely heating or scalding breast milk, particularly milk intended for a young or medically vulnerable baby, discuss the appropriate method with a qualified lactation or healthcare professional.

And importantly, scalding is a preventative strategy. Heating milk after an unwanted taste has already developed won’t necessarily reverse the changes that have already occurred.

Can Freeze-Drying Help With High Lipase Breast Milk?

Freeze-drying is another option families may consider when their baby refuses conventionally frozen milk.

During freeze-drying, frozen breast milk is placed under vacuum and water is removed primarily through sublimation — the transition of ice directly into water vapour.

The resulting freeze-dried breast milk is converted into a dry form that can later be reconstituted with water.

At Nourishy, we have seen encouraging results with milk from mothers whose babies previously refused their frozen stash because of the taste associated with high lipase milk.

In our own testing, 9 out of 10 babies who had previously refused their mother’s thawed high-lipase milk subsequently accepted that milk after it had been professionally freeze-dried and reconstituted.

This is an observation from our own testing and should not be interpreted as a guarantee that freeze-drying will change the taste of every mother’s milk or that every baby will accept it.

Human milk varies from mother to mother, and babies have individual taste preferences.

What Happens to Lipase During Freeze-Drying?

This deserves some clarification because freeze-drying is sometimes described too simply.

Freeze-drying removes water at low temperatures rather than using the high temperatures associated with conventional heat drying.

However, freeze-drying should not be described as permanently destroying or completely deactivating all lipase in human milk.

Published research has demonstrated measurable lipase activity in freeze-dried human milk under some processing and storage conditions.

A more useful way to think about freeze-drying is that removing water dramatically changes the environment in which biological and chemical reactions can occur while the milk remains in its dried state.

At Nourishy, each customer’s milk is professionally freeze-dried, individually processed and packaged to protect the resulting powder from environmental moisture.

For families dealing with a frozen stash their baby refuses because of its taste, professional freeze-drying therefore provides another option worth considering.

Can Freeze-Drying Fix Milk That Already Tastes Soapy or Metallic?

This is an important distinction.

Freeze-drying should not be thought of as a process that magically reverses every flavour change that has already occurred during months of frozen storage.

If fats in the milk have already undergone changes before the milk reaches the freeze-dryer, removing the water does not simply turn back time.

However, our experience has shown that some babies who refused their mother’s conventionally frozen high-lipase milk subsequently accepted the same milk once it had been freeze-dried and reconstituted.

Because every mother’s milk and every baby’s preferences are different, results can vary.

If you have a particularly large stash that your baby currently refuses, contact Nourishy before deciding what to do with it.

Does Freeze-Drying Preserve Breast Milk?

Professional freeze-drying removes sufficient water to produce a shelf-stable product when the milk is appropriately processed, tested, packaged and stored.

At Nourishy, breast milk is processed individually rather than pooled with milk from other mothers.

Our process also includes water activity testing and protective packaging designed for long-term storage.

Freeze-drying isn’t sterilisation, and the quality of the milk entering the process still matters. Safe expression, freezing, transport, processing and storage all remain important.

For families who have accumulated a significant frozen breast milk stash, freeze-drying can provide an alternative to continuing to store that milk in the freezer.

For more detail on the science and quality controls involved, read Is Freeze-Dried Breast Milk Safe? and our guide to freeze-dried breast milk shelf life and storage.

What If My Baby Still Won’t Drink High Lipase Milk?

Babies have preferences just like adults.

If your baby refuses stored milk, don’t immediately assume the entire stash needs to be discarded.

Depending on your circumstances, options may include:

• Offering freshly expressed milk when possible
• Testing how quickly your milk develops a taste or smell change
• Trying a mixture of fresh and appropriately stored milk
• Discussing scalding freshly expressed milk with a lactation professional
• Professionally freeze-drying your frozen stash
• Exploring whether you are eligible to donate suitable milk through an approved milk bank

The right solution will depend on the age and needs of your baby, how much milk you have stored, when the flavour change occurs and whether your baby will accept it.

Can You Donate High Lipase Breast Milk?

Potentially, but milk banks have strict donor eligibility, screening, collection and storage requirements.

You cannot assume that milk will be accepted simply because it is suitable for your own baby.

Approved donor human milk is processed according to the milk bank’s protocols, which commonly include donor screening, testing and pasteurisation. Australian milk banks use strict processes to protect the infants receiving donated milk. [oai_citation:1‡Pregnancy Birth Baby](https://www.pregnancybirthbaby.org.au/babies/feeding-and-nutrition/donor-breast-milk-and-milk-banks?utm_source=chatgpt.com)

If you’re interested in donating, contact the milk bank before making plans for your stash so they can assess your eligibility and explain their requirements.

Nourishy works alongside Mothers Milk Bank Charity in Australia, which supports families and vulnerable infants through screened donor human milk.

Frequently Asked Questions About High Lipase Milk

What does high lipase breast milk smell like?

Parents commonly describe stored breast milk affected by storage-related flavour changes as soapy, metallic, sour or otherwise different from freshly expressed milk. An unusual smell does not by itself prove that the milk has high lipase or that it has spoiled.

What does high lipase breast milk taste like?

Descriptions include soapy, metallic, bitter or occasionally rancid-tasting. The taste can vary considerably between mothers and may change depending on how long the milk has been stored.

Is high lipase milk bad for babies?

Lipase itself is a normal component of human milk. If stored milk develops a different flavour but has otherwise been expressed, handled and stored appropriately, the taste difference does not automatically mean the milk is unsafe. Some babies drink it without any problem, while others refuse it.

Why does my breast milk smell fine when fresh but strange after freezing?

Enzymes and other components of human milk can remain active after expression, and changes in milk fats can occur during storage. Freezing does not necessarily eliminate lipase activity, which can contribute to differences between freshly expressed and stored milk.

Can I prevent high lipase breast milk?

High lipase isn’t generally something a mother needs to “cure”. Lipase is naturally present in breast milk. If your concern is that stored milk develops a flavour your baby refuses, identifying how quickly the change occurs can help you decide on an appropriate storage strategy.

Does scalding breast milk stop lipase?

Heating human milk can reduce lipase activity, which is why scalding has traditionally been suggested for mothers whose stored milk develops an unwanted flavour. Heating can also affect other heat-sensitive components of breast milk, so seek appropriate professional advice before making it part of your routine.

Can I scald breast milk after freezing?

Scalding is generally discussed as a strategy used on freshly expressed milk before storage. Once lipolysis has already changed the fats and flavour of stored milk, later heating cannot necessarily reverse those changes.

Does freeze-drying deactivate lipase?

It would be too simplistic to say that freeze-drying permanently deactivates all lipase. Research has found measurable lipase activity in freeze-dried human milk. Removing water does, however, substantially change the environment in which reactions occur while the milk remains dry.

Will freeze-drying make my high lipase milk taste better?

Results can vary. At Nourishy, 9 out of 10 babies in our own testing who had refused their mother’s thawed high-lipase milk accepted it after freeze-drying and reconstitution. This is an observation from our own testing rather than a guarantee that every baby will respond in the same way.

Is high lipase milk the same as spoiled milk?

No. A storage-related change in smell or taste is not automatically evidence of spoilage. However, you should not assume every unusual smell is caused by lipase either. Milk still needs to have been expressed, handled and stored safely.

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The Bottom Line

High lipase milk can be frustrating, especially when you discover the issue after spending months pumping and building a freezer stash.

But a soapy or metallic taste does not automatically mean all that breast milk needs to go to waste.

Lipase is a natural component of human milk, and changes in taste and smell can occur as expressed milk is stored. Some babies don’t mind the difference at all. Others strongly prefer freshly expressed milk.

If your baby refuses stored milk, start by working out when the taste changes. You can then explore options such as changing how you rotate your stash, combining fresh and stored milk, discussing scalding with an appropriate professional, donating eligible milk, or professionally freeze-drying your stash.

For families facing the heartbreaking prospect of throwing away a freezer full of breast milk their baby refuses, freeze-drying may offer another option.

At Nourishy, we professionally freeze-dry each family’s own breast milk individually, helping transform a difficult-to-use frozen stash into a convenient powdered format designed for long-term storage.