Mayo Clinic Health Library

Breast milk storage: Do's and don'ts

Updated: 04-06-2012

If you're breast-feeding your baby and going back to work or looking for more flexibility, you're probably considering using a breast pump. Once you start pumping, it's important to know how to safely and properly store your expressed breast milk. Consider these do's and don'ts for breast milk storage.

What kind of container should I use to store expressed breast milk?

Before expressing or handling breast milk, wash your hands with soap and water. Then store the expressed milk in a clean, capped glass or hard plastic container. You can also use special plastic bags designed for milk collection and storage. Keep in mind that breast milk storage bags aren't generally recommended for long-term storage because they might spill, leak and become contaminated more easily than hard-sided containers. For extra protection, you can place the bags in a hard plastic food storage container with a tightly sealed lid. Also, certain components of breast milk might adhere to the soft plastic bags during long-term breast milk storage, which could deprive your baby of essential nutrients.

Don't store breast milk in disposable bottle liners or plastic bags designed for general household use.

What's the best way to store expressed breast milk?

Using waterproof labels and ink, label each container with the date you expressed the breast milk. If you're storing expressed milk at your baby's child care facility, add your baby's name to the label. Place the containers in the back of the refrigerator or freezer, where the temperature is the coolest. If you don't have access to a refrigerator or freezer, store the milk in a cooler or insulated bag until you can transfer the milk to the refrigerator or freezer.

To minimize waste, fill individual containers with the amount of milk your baby will need for one feeding. You might start with 2 to 4 ounces (59 to 118 milliliters), and then adjust as needed. Also consider storing smaller portions — 1 to 2 ounces (30 to 59 milliliters) — for unexpected situations or delays in regular feedings. Keep in mind that breast milk expands as it freezes, so don't fill containers to the brim.

Can I add freshly expressed breast milk to already stored milk?

You can add freshly expressed breast milk to refrigerated or frozen milk you expressed earlier in the same day. However, be sure to thoroughly cool the freshly expressed breast milk in the refrigerator or a cooler with ice packs before adding it to previously chilled or frozen milk. Don't add warm breast milk to frozen breast milk because it will cause the frozen milk to partially thaw. Keep milk expressed on different days in separate containers.

How long does expressed breast milk keep?

How long you can safely keep expressed breast milk depends on the storage method. Consider these general guidelines for healthy infants:

  • Room temperature. Freshly expressed breast milk can be kept at room temperature for up to six hours. If you won't use the milk that quickly or the room is especially warm, transfer the milk to an insulated cooler, refrigerator or freezer.
  • Insulated cooler. Freshly expressed breast milk can be stored in an insulated cooler with ice packs for up to one day. Then use the milk or transfer the containers to the refrigerator or freezer.
  • Refrigerator. Freshly expressed breast milk can be stored in the back of the refrigerator — not the door — for up to five to eight days.
  • Freezer. Freshly expressed breast milk can be stored in a standard refrigerator freezer for up to three to six months and in a chest freezer for up to six to 12 months. Place the milk in the back of the freezer — not the door.

Expressed breast milk is an ideal way to feed your baby when you're apart. Still, some research suggests that the longer you store breast milk — whether in the refrigerator or in the freezer — the greater the loss of vitamin C in the milk. Other studies have shown that refrigeration beyond two days might reduce the bacteria-killing properties of breast milk and long-term freezer storage might lower the quality of fat in the breast milk. It's also important to note that breast milk expressed when a baby is a newborn won't as completely meet the same baby's needs when he or she is older.

Keep in mind that storage guidelines might differ for preterm, sick or hospitalized infants.

How do I thaw frozen breast milk?

Thaw the oldest milk first. Simply place the frozen container in the refrigerator the night before you intend to use it. You can also gently warm the milk by placing it under warm running water or in a bowl of warm water. Before offering the milk to your baby, gently swirl it to evenly distribute the creamy portion of the milk that rises to the top of the container during storage. Don't vigorously shake the container or stir the milk.

Never thaw frozen breast milk at room temperature, which enables bacteria to multiply in the milk. Also, don't heat a frozen bottle in the microwave or very quickly on the stove. Some parts of the milk might be too hot, and others too cold. Some research suggests that rapid heating can affect the milk's antibodies as well.

Use thawed breast milk within 24 hours. Discard any remaining milk. Don't refreeze thawed or partially thawed breast milk.

Does thawed breast milk smell or look different from fresh breast milk?

The color of your breast milk might vary, depending on your diet. Also, thawed breast milk might seem to have a different odor or consistency than freshly expressed milk. It's still safe to feed to your baby. If your baby refuses the thawed milk, it might help to shorten the storage time.

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