Proper handling and storage of expressed breast milk are paramount to preserving its beneficial properties and ensuring infant safety. Understanding these guidelines is important for providing optimal nutrition and protection for a baby.
Combining Fresh and Stored Breast Milk
A common question is whether freshly expressed milk can be added to milk that is already chilled or frozen. Health organizations, such as the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP), advise against adding warm, freshly expressed breast milk directly to cold or frozen milk. The primary concern is that warmer milk can raise the temperature of the already cooled milk, potentially promoting bacterial growth.
To combine milk from different pumping sessions, cool the freshly expressed milk to refrigerator temperature first. This is achieved by placing the warm milk in the refrigerator until it reaches the same chilled temperature as the previously stored milk. Once the temperatures are equalized, the cooled fresh milk can then be safely added to refrigerated or frozen milk.
Some research suggests that mixing milk from different pumping sessions, even at varying temperatures, may not significantly increase bacterial counts if pooled within a 24-hour period, and can help even out nutrient variability. However, the established guidelines prioritize cooling to minimize any potential risk.
Understanding Temperature Zones and Bacterial Growth
The rationale behind temperature control for breast milk storage is the “danger zone” for bacterial proliferation, a range between 40°F and 140°F (4°C and 60°C) where bacteria multiply rapidly.
While breast milk contains antimicrobial properties that help inhibit bacterial growth, prolonged exposure to temperatures within this range can compromise its safety and quality.
When warm breast milk is added to cold milk, it can temporarily raise the overall temperature of the stored milk into this danger zone, even if briefly. This temperature fluctuation could potentially encourage the multiplication of any existing bacteria, even non-pathogenic ones, thereby increasing the risk of contamination.
Maintaining consistent, cool temperatures helps to slow bacterial growth, preserving the milk’s integrity and reducing the likelihood of spoilage or harm to the infant.
General Guidelines for Breast Milk Storage and Thawing
General guidelines ensure the safe storage and thawing of expressed breast milk.
Freshly expressed breast milk can be stored at room temperature (up to 77°F or 25°C) for up to four hours. It should be chilled or frozen as soon as possible after expression.
For refrigeration, freshly expressed milk can be stored in the back of the refrigerator, where temperatures are most consistent, for up to four days at 40°F (4°C) or colder. If not used within this timeframe, it should be frozen.
Frozen breast milk can be stored in a standard freezer for up to six months, with some guidelines extending acceptable storage up to 12 months in a deep freezer, though earlier use within six months is often recommended for best quality.
When thawing frozen breast milk, the safest methods involve placing it in the refrigerator overnight, or by holding the container under cool or lukewarm running water. It can also be placed in a bowl of warm water. Thawed milk should never be refrozen.
Microwaving breast milk or heating it directly on a stove is not recommended, as this can create hot spots that may burn a baby’s mouth and can destroy some of the milk’s beneficial nutrients and antibodies. Once thawed, refrigerated milk should be used within 24 hours, and milk brought to room temperature or warmed should be used within two hours.