Breast milk is packed with immune-boosting antibodies and vital nutrients for your baby's cognitive and physical development. Even if you're breastfeeding exclusively, many mothers find it necessary at some point to pump and store breast milk for later feedings. According to La Leche League, breast milk stored in a bottle at room temperature (between 66 and 78 degrees Fahrenheit) stays fresh for up to four hours and is usable for up to six hours. Refrigerated breast milk stays fresh for 72 hours but is usable for up to eight days. Frozen breast milk remains fresh for six months and usable for 12. If you find yourself unsure about freshness, a few simple tests can determine whether your breast milk has expired.
Examine the breast milk in its storage container, then swirl it around. Fresh breast milk often separates into two layers after sitting a while; however, these layers should disappear when you swirl the container. Breast milk that remains separated after swirling is probably spoiled. Curdling is another indicator that your breast milk has gone bad.
Open the container and smell the milk. Soured breast milk has a similar rancid odor to soured cow's milk. Simply having an odor does not necessarily indicate soured milk, but if the breast milk smells rancid or spoiled -- and like cow's milk, it's a hard odor to mistake -- consider the milk spoiled. It's important to note that even if your breast milk doesn't smell bad but still has one of the spoil indicators mentioned above, it's safest to discard it.
Taste the breast milk. Even though the flavor of fresh breast milk may not appeal to you, breast milk that's gone bad has a unmistakably sour taste similar to spoiled cow's milk. If your milk passes each of these tests, it's unlikely to have spoiled and is safe to feed to your baby.