Storing milk: times, containers and the freezer

Storage times are one of the few parts of pumping with clear published guidance, so there is no reason to guess or to trust a number a brand made up. The figures here follow the CDC recommendations for healthy full-term babies. If your baby was premature, is in hospital care, or has a medical condition, your care team gives you different numbers and theirs are the ones to use.

Freshly expressed milk

Where	How long
Room temperature, up to 77 F (25 C)	Up to 4 hours
Refrigerator, 40 F (4 C)	Up to 4 days
Freezer, 0 F (-18 C) or colder	Best within 6 months, acceptable up to 12

Source: CDC guidance on proper storage and preparation of breast milk. The 4 hour and 4 day figures are limits, not targets. Milk that will not be used within a day or two is better off frozen early, while it is at its freshest, than frozen on day four.

Once it has been thawed

Thawed milk keeps in the fridge for up to 24 hours and at room temperature for 1 to 2 hours. It does not go back in the freezer. If a feeding was started and not finished, the leftovers should be used within 2 hours and then discarded.

Containers and filling

Bags or hard containers both work, as long as they are meant for milk storage. Leave headroom at the top of the container, because milk expands as it freezes and a full bag splits at the seam. Store in the amount your baby actually takes in one feed rather than in large batches; thawing 5 oz to use 2 oz wastes the other 3.

Bags freeze flat and stack. That is not a tidiness point, it is a capacity point: flat bags thaw faster and fit a freezer shelf about three times better than bags frozen upright.

Labels

Date every container as it goes in, and use the oldest first. Write the date the milk was expressed, not the date it went into the freezer, since those are often different days. If the milk is going to a daycare, the baby's name goes on the label as well.

Thawing

Overnight in the fridge, or under warm running water for something faster. Not in a microwave: it heats unevenly, and the hot spots are the exact problem. Swirl rather than shake to mix the separated layer of fat back through, which is normal separation and not spoilage.