The milk that we buy at the grocery store has been pasteurized and homogenized. The pasteurization process kills all the bacteria and live cells in the milk—making it safe for us to drink, but also less stable. Homogenizing the milk blends in the fat so that it doesn’t separate and float to the top. Most of us don’t have experience using fresh milk straight from the source. Fresh milk from any mammal—including humans—looks very different from the milk we buy at the store.

After your milk has been expressed and it has been sitting on the counter or in the refrigerator for a while, the fat will begin to separate. You may notice a thin layer of cream on top of milk that looks quite watery. That is perfectly normal. Your milk has not gone “bad.”

Since fat content varies by the time of day, the fat layer may range from just barely visible to a half-inch or more. Milk fat content also varies widely among mothers, so expect to see a difference. Any amount of fat you see in the milk is perfect! There is no need for concern that your milk isn’t “good enough” for your baby.

To Use Stored Milk:

• Shake or swirl the milk gently before giving it to your baby in order to mix in the cream.  It’s normal to see little bits of fat floating in the milk after mixing.

• If it’s been refrigerated, you can gently warm it to room temperature in a bowl of hot water. You may not even need to warm it! Many babies are just as happy with cold milk.

• Frozen milk can be thawed in container of hot water.  If you have time, it can be thawed slowly in the refrigerator. Use previously frozen milk within 24 hours of complete thawing. If your milk is partially thawed, (still ice in the milk) it can be re-frozen to be used at another time.

• Never use a microwave to thaw or warm your milk. It may produce hot spots in the milk that can burn your baby. In addition, important nutrients will be destroyed if the milk gets too hot.

• If you baby doesn’t finish his bottle of 100% breast milk, it’s likely fine to offer it to him again at the next feeding. Unfortunately, there is no definitive research regarding re-using human milk. Most sources say that “it’s probably safe.” Unused formula, however, must be discarded.

•  For additional information, see Breast Milk Storage Guidelines.