The Normal Scent of Breastmilk
Freshly expressed breastmilk generally has a very mild scent, often described as mildly sweet. However, its smell and taste can be influenced by the mother's diet, taking on a hint of strong-flavored foods like garlic or spices. This is completely normal and doesn't affect the milk's safety or nutrition. Some mothers also notice a creamy or slightly fatty scent, which is also a normal characteristic of human milk.
Why Does Stored Breastmilk Develop a Smell?
Stored breastmilk, whether refrigerated or frozen, can undergo natural changes that alter its odor. These changes do not automatically mean the milk is spoiled. There are two primary reasons for 'off' smells in safely stored milk, along with the distinct smell of actual spoilage.
High Lipase Activity
Lipase is a natural enzyme found in human milk that helps break down fats into smaller particles, making them easier for the baby to digest. All breastmilk contains lipase, but some women have higher levels of this enzyme, leading to a more noticeable effect during storage. When high lipase activity occurs, stored milk can develop a soapy, metallic, or sometimes fishy odor and taste. While the scent and flavor may be unpleasant to some babies, high-lipase milk is not spoiled and remains safe and nutritious. The longer the milk is stored, the stronger the high-lipase odor can become.
Chemical Oxidation
In some cases, stored breastmilk can develop a rancid smell and taste due to chemical oxidation. This reaction can occur when unsaturated fatty acids in the milk are exposed to air or certain minerals, like copper or iron, in the mother's water supply. Dietary factors, such as supplements containing fish oil or flaxseed, may also play a role. Unlike high-lipase milk, which often smells soapy or metallic, oxidized milk is more likely to smell and taste distinctly rancid. While often still considered safe, babies might refuse milk affected by oxidation.
True Spoilage from Bacteria
The most important distinction to make is between milk that has an altered but safe scent and milk that is truly spoiled. True spoilage results from bacterial contamination due to improper storage or handling, such as leaving milk out for too long or using unclean equipment. This is when breastmilk starts to smell strongly sour or rotten, much like expired cow's milk. Any milk with this distinct, foul odor should be discarded immediately, as feeding it to a baby can cause health issues like vomiting, diarrhea, or food poisoning.
How to Differentiate Between High Lipase and Spoiled Milk
It can be confusing to discern if an unusual scent is just high lipase or actual spoilage. Here's a table to help compare the key differences:
| Characteristic | High Lipase Milk | Spoiled Milk |
|---|---|---|
| Smell | Soapy, metallic, or sometimes fishy or sour. Increases in intensity over time but does not smell rotten. | Distinctly sour or rotten, similar to spoiled dairy milk. Unpleasant and strong from the outset. |
| Appearance | May separate into layers but will reintegrate smoothly when swirled. Color may vary (bluish, yellowish). | May have persistent clumps or chunks that do not mix back in when swirled. Can also show unusual colors like green or orange. |
| Taste | Altered taste, often described as soapy or metallic, but not truly rancid. | Tastes distinctly sour and unpleasant. |
| Safety | Considered safe and nutritious for the baby, though they may refuse it. | Not safe for consumption; must be discarded immediately. |
What to Do About High Lipase Breastmilk
If you have determined that the odd smell is due to high lipase rather than spoilage, there are several methods you can use to address it.
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Scald Freshly Expressed Milk: Scalding is the most effective way to prevent the development of a soapy or metallic taste. Heat freshly expressed milk to about 180°F (82°C)—the point where bubbles form around the edges of the pan—and then quickly cool it. This process deactivates the lipase enzyme. It's important to do this before freezing the milk.
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Mix Stored and Fresh Milk: If your baby is sensitive to the taste of high-lipase milk, you can try mixing it with an equal part of freshly expressed milk to dilute the altered flavor. This can make the milk more palatable.
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Consider Serving Chilled: Some babies are less bothered by the altered taste when the milk is served cold or at room temperature, as opposed to warmed.
Safe Breastmilk Storage Practices
Preventing true spoilage is paramount and relies on proper storage techniques. Following guidelines from health organizations like the CDC and the Mayo Clinic is essential.
- Cleanliness: Always wash your hands thoroughly with soap and water before handling breastmilk or pumping equipment. Ensure all containers and pump parts are clean and sanitized.
- Container Choice: Use food-grade glass or hard plastic containers with tight-fitting lids, or special breastmilk storage bags. Avoid using disposable bottle liners or general-purpose plastic bags.
- Labeling and Rotation: Always label milk with the date it was expressed. Use the oldest milk first to ensure the best quality and reduce waste.
- Optimal Fridge and Freezer Placement: Store milk in the back of the refrigerator or freezer, as this area maintains the most consistent temperature. The door is not ideal due to frequent temperature fluctuations.
- Thawing Guidelines: Always thaw milk in the refrigerator overnight or by placing the container in warm water. Never use a microwave, which can create hot spots and destroy nutrients. Thawed milk should not be refrozen.
Conclusion
While it can be alarming to open a container of stored breastmilk and discover an unusual scent, it is often due to the benign, high-lipase enzyme rather than dangerous spoilage. By recognizing the key differences—a soapy or metallic scent for high lipase versus a distinctly sour, rotten odor for spoilage—parents can confidently determine if milk is safe for their baby. Following strict hygiene and storage guidelines is the best way to prevent bacterial contamination and ensure your baby receives the highest quality milk. When in doubt, it is always safest to discard any milk that smells or looks truly spoiled. For further reading on breastmilk storage guidelines, consult the CDC's official page: https://www.cdc.gov/breastfeeding/breast-milk-preparation-and-storage/handling-breastmilk.html.
