This article is medically reviewed by Dr. Tran Thi Mai Huong, Specialist Level II, Department of Obstetrics and Gynecology, Vinmec International General Hospital, Hai Phong.
Breast milk contains all the necessary nutrients—sugars, proteins, fats, vitamins, and minerals—in ratios ideal for the absorption and development of infants. For this reason, even when mothers don’t have enough time for breastfeeding, many still express and store breast milk for future use. However, during storage, due to various reasons, thawed breast milk may develop a sour smell or unusual taste. So how can mothers determine whether the milk is safe for consumption when such abnormalities occur?
1. How to Identify Spoiled Breast Milk
Some signs of spoiled breast milk can be detected through observation and sensory examination:
Thawed Breast Milk with a Sour Smell
Fresh breast milk typically has an ivory-white color and a pleasant, mild fragrance, distinctly different from other types of milk. If you open a storage container or bag and detect a fishy, sour, or otherwise unpleasant odor, the milk has likely spoiled or exceeded its shelf life.
Causes of Sour-Smelling Breast Milk:
- Dietary Choices: Consuming strong-smelling foods such as fish, fish oils, or spices like garlic and chili can affect the odor and flavor of breast milk, potentially making it sour.
- Excessive use of antibiotics
- Poor Hygiene: Improperly cleaned breasts, where residual milk remains on the skin, can sour and emit an unpleasant odor, providing an environment conducive to mold and bacteria that could affect the milk's quality.
- Improper Storage: If breast milk is stored inappropriately in the refrigerator or if unclean storage containers or breast pumps are used, the milk's quality and odor can deteriorate. In cases where sour milk is due to poor storage practices, it should never be given to the baby.
Breast Milk with a Layer of Fat
The high-fat content in breast milk can cause it to develop a layer of cream, which is normal. However, this requires careful observation.
If shaking the container reintegrated the cream into the milk, it indicates the milk is still of good quality and can be warmed using a double boiler before feeding.
Conversely, if the cream layer floats separately and does not mix even when shaken, the milk is likely spoiled and should not be fed to the baby.
Note: Sometimes, thawed milk may appear to have white sediment. This is also normal and not a cause for concern; it often occurs due to the mother's low water intake, resulting in denser milk. Adjusting hydration levels can resolve this issue, and the milk remains safe for consumption.
Unusual Taste or Odor
In addition to visual and olfactory checks, mothers can taste the milk. Under normal conditions, breast milk has a characteristic mild, slightly creamy flavor, without being overly salty or sweet. If it tastes fishy, sour, or has an unpleasant smell, the milk has likely spoiled, and its nutritional integrity is compromised.
Storage Time Exceeded
Breast milk has specific storage times depending on the storage conditions. Many mothers label milk bags with the date and time of expression for tracking.
If the milk exceeds the recommended storage duration when thawed, it should be discarded, even if it appears otherwise normal.
Abnormal Reactions in the Baby
Infants have highly sensitive taste perception. If, after thawing and feeding, the baby shows signs of rejecting the milk or becomes irritable when forced to drink, this could indicate the milk has spoiled or lost its quality, making it unpalatable to the baby.
2. Causes of Spoiled Breast Milk
- All equipment related to pumping, expressing, and storing breast milk for babies must be thoroughly sterilized and hygienic. Failure to do so can cause breast milk to spoil right after being expressed. Using substandard or unverified storage containers can also pose significant risks.
- Some mothers, for convenience, often place milk in the refrigerator door, where the temperature is not cold enough and allows for easier thawing. However, frequently opening and closing the refrigerator door to access food can lead to inadequate storage temperatures, facilitating bacterial growth and causing the milk to spoil faster.
- If breast milk is stored for too long, the nutritional content, including vitamin C and minerals, will gradually degrade over time. Storing it past the recommended time may lead to spoiled milk, which can negatively impact the baby.
- Overfilling milk in storage containers or bags can also result in faster spoilage. Since milk expands when frozen, overfilled containers may burst or spill, leading to contamination. Experts recommend filling only about ¾ of the container to allow room for expansion.
- Mixing previously stored milk with freshly expressed milk is another reason for faster spoilage. The temperature difference between the two batches can compromise the quality and preservation of the breast milk.
- Heating breast milk using a microwave, while quick, is not suitable. Microwaves do not heat the milk evenly and can destroy some of the antibodies in the milk, adversely affecting its quality.
- Some mothers mistakenly believe that thawing milk by leaving it out at room temperature is acceptable. However, this inadvertently creates an environment conducive to bacterial growth, compromising the milk's quality and potentially leading to spoilage.
3. Risks of Feeding Babies Spoiled Breast Milk
Infants have underdeveloped digestive and immune systems. Consuming spoiled or expired milk can lead to severe consequences, such as:
- Diarrhea: Similar to food poisoning in adults, spoiled breast milk can cause digestive upset in infants.
- Vomiting: Milk spoilage may trigger vomiting, a common symptom of foodborne illness.
- Stomach Cramps: Spoiled milk can lead to abdominal pain, bloating, and irritability.
- Food Poisoning: Contaminated milk can cause bacterial infections, leading to severe diarrhea, vomiting, or even life-threatening conditions.
4. Tips for Proper Breast Milk Storage
If mothers have the means and time, direct breastfeeding is still the best and safest option. However, in cases where milk must be expressed and stored, proper preservation according to the following guidelines is crucial:
- Sterilize equipment, bottles, and storage bags thoroughly to ensure hygiene before use.
- Store expressed breast milk in the freezer, the coldest part of the refrigerator. If you do not plan to use the milk immediately, place it in the refrigerator as soon as possible.
- Breast milk storage temperature guidelines:
- At room temperature (25°C): 4–6 hours.
- At 15°C: 24 hours.
- At 22°C: 10 hours.
- In a regular refrigerator, in the cooler compartment (0°C to -4°C): 2–3 days.
- In a regular freezer below -5°C: 2 weeks.
- In a standalone freezer below -18°C: 3–6 months.
- In a standalone freezer below -20°C: 6–12 months.
- When preparing milk for the baby, avoid direct heating. Instead, thaw it gradually by placing the bottle or storage bag in warm water or under running warm water.
- Before feeding, check the milk for any unusual odor, separation, or strange taste to ensure it is safe for the baby.
- Once thawed, breast milk should be used within 5 days if re-stored in the refrigerator.
- Avoid re-freezing used milk as this can degrade the lipid content, reducing its quality and potentially causing spoilage.
Hopefully, the information above helps mothers identify spoiled or expired breast milk and avoid using it for their babies, which could negatively impact their health. If it is not feasible to breastfeed directly 100% of the time, proper storage methods must be implemented to ensure the baby receives the full benefits of breast milk.
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