In their Keeping Kids Healthy column, UTMB Drs. Sally Robinson and Keith Bly provide guidelines on storing and preserving breast milk for a healthy infant. Fresh or pumped milk placed in a refrigerator set at 39 degrees will remain usable for 72 hours. Milk pumped at work and placed in a cooler along with some refreezable ice and kept at 59 degrees will remain usable for 24 hours. At room temperature, which is 77 degrees, the milk will last only about four hours. Do not thaw milk in the microwave. Doing so will destroy much of the immunologic benefit. To thaw a container of breast milk, move it to the refrigerator the day before, leave it at room temperature, place it in lukewarm water, or place it under warm running water.