Many moms have similar questions about storing their breastmilk. I've answered some of the most-commonly asked questions: How long can breastmilk be left at room temperature? Studies have shown that freshly expressed breastmilk can be stored at room temperature, (79 degrees F), for up to six hours, (Hamosh 1996) or at 66 to 72 degrees for up to 10 hours (Barger and Bull 1987). I usually recommend leaving breastmilk at room temperature for no more than four hours. Breastmilk varies from mother to mother, and room temperature is often a subjective measure that varies over time. How long can your milk be safely refrigerated? If you are not going to use breastmilk within four hours after pumping, refrigerate or freeze it as soon as possible. If the milk is refrigerated at 32 to 39 degrees Fahrenheit it can be stored for up to eight days (Pardou 1994) How long can you keep breastmilk in the freezer? Frozen breastmilk can be stored three to six months, depending on the temperature of the freezer and frequency of freezer door openings. Deep freezers, or chest freezers afford the longest freezing time because of they usually have lower and more consistent temperatures. Do not store breastmilk on a freezer or refrigerator door, since that's where the widest temperature variations occur. What type of container is best for storing your milk? There are a variety of containers for breastmilk storage. For most healthy, term babies, who get the bulk of their nutrition from direct breastfeeding, the storage container is not as important as it might be for a hospitalized preemie or ill baby who is getting only expressed milk. Glass is usually considered the best choice for freezing milk because the components of milk are better preserved in glass. Second choice would be hard, clear plastic containers. Most moms find plastic is more convenient and some day-care centers will not accept glass because of the risk of breakage. All containers should have a tight sealing, one piece lid. Storing breastmilk in milk storage bags could present some problems. The milk could cling to the sides of the storage bag, reducing the amount that gets to baby. Milk bags are also more prone to contamination through leakage. Some pump companies make milk storage bags that are very convenient to use and are of a thicker gauge plastic than those originally tested, however, these can be expensive. If you do use bags, it's a good idea to double bag the thinner ones and store any bag in a hard plastic storage container with a lid, in the freezer. This will help reduce the risk of small tears in the bag. Ask your day-care provider that when they warm bagged milk, not to allow the water over the top of the bag, since this will likely cause water to enter the bag as it is opened. If the water used for warming becomes cloudy, that indicates a leak and the bag of milk must be discarded (Mohrbacher, & Stock 1997). Colored baby bottles should not be used as some of the dyes may enter the milk. How will you know what milk should be used first? Always label your milk with the date it was expressed and use the "oldest" stock first. If you provide milk for your baby in a day-care center, make sure your babies' name is clearly visible to avoid mix-ups. How much milk should be stored for a feed? I recommend that mothers of babies under six weeks store their milk in small increments of one to two ounces per container, so that warming time is short and less milk is discarded. As the baby gets older, milk can be stored in the amount that your baby usually drinks at a feeding, but it is still a good idea to keep some small amounts available for those times when the baby wants a little more or for a little snack when mom is expected home soon and will want to breastfeed. Is it safe to save your breastmilk after offering to baby? There has only been one small study of breastmilk that has been stored, warmed and partially consumed by babies. It suggests that it is safe to feed previously stored milk up to one or two hours after it has been prepared. Any unused portion should then be discarded. References: Barger, J. and Bull, P.A., Comparison of the bacterial composition of breast milk stored at room temperature and stored in the refrigerator. Intl Journal of Childbirth Ed 2: pages 29 and 30 1987. Hamosh, M. et al., Breastfeeding and the working mother effect of time and temperature of short term storage on proteolysis, lipolysis, and bacterial growth in milk. Pediatrics 97 (4) 492 to 498, 1996 Mohrbacher, N. and Stock, J., The Breastfeeding Answer Book, La Leche League International, 1997, pp 30 to 31. Pardou, A. et al., Human milk banking: influence of storage processes and of bacterial contamination on some milk constituents. Biol Neonate 65:302 to 309, 1994