NOTE: These guidelines apply for mothers who have healthy full-term babies (check with your hospital personnel for guidelines pertaining to storage and handling of breastmilk for pre-term or ill babies).

Human milk has been found to have properties that protect it from bacterial contamination which allow it to be stored longer than was previously thought. Guidelines for breastmilk storage are as follows:

• Freshly expressed breastmilk may be kept at room temperature for up to 10 hours (colostrum or milk expressed within 6 days of delivery can be stored 12 hours at room temperature).

• Freshly expressed milk may be stored at temperatures slightly below room temperature (such as in a cooler with icepacks ) for up to 24 hours. If the milk has been kept at room temperature prior to being placed into the cooler, safe storage time in the cooler may be decreased somewhat.

• Fresh breastmilk may be kept in a refrigerator for up to 8 days. Store milk in the back of the refrigerator rather than in the door. If milk has been kept at room temperature or in a cooler with icepacks prior to being placed in the refrigerator, safe storage time may be decreased.

• Fresh milk may be placed in a freezer compartment inside a refrigerator for up to 2 weeks. If it has previously been kept at room temperature, in a cooler, or in the refrigerator, storage time may vary.

• Freshly expressed breastmilk may be kept in a self-contained freezer unit of a refrigerator for up to 3-6 months, depending upon how often the door is opened. Store milk in the back of the freezer. If the milk has been stored at room temperature, in a cooler with icepacks, or in the refrigerator prior to being placed in the freezer, safe freezing time may be decreased.

• Fresh milk may be placed in a separate deep freeze (chest-type freezer) for 6-12 months. If previously kept at room temperature, or stored in a cooler or refrigerator before freezing, storage time may vary.

• Previously frozen milk may be kept in the refrigerator for up to 24 hours after it has completely thawed..

One last word about the guidelines: Although the above is the latest published set of guidelines regarding safe storage times of breastmilk, keep in mind that these are just guidelines. It's wise to try to stay as close to them as possible, but milk that is older than the stated safe age, should not be automatically discarded. Milk that is truly bad has a very distinct sour taste and odor. Even if expressed milk is "out of date" it should still be considered safe to give a baby as long as it still has a fresh odor and/or taste.

When a baby is only receiving expressed milk occasionally, the type of storage container is not a major consideration; however, if a baby is receiving most of his nourishment from expressed breastmilk, the type of storage container used should be considered carefully. Plastic containers are the best choice for storing breastmilk in the refrigerator as more of human milk's leukocytes or white cells adhere to glass. If the milk is to be frozen, glass is the preferred choice as it is less porous and offers the best protection. Most of the leukocytes in human milk are killed with freezing anyway. For this reason, milk that can be used within 8 days of expression should be refrigerated rather than frozen, because the antimicrobial properties of human milk are better preserved with refrigeration.

Another good choice for refrigeration or freezing is the milk storage bags that are designed specifically for human milk (see CSF milkbags). They are pre-sterilized and are thicker (2-ply), coated with polyethylene, and lined with nylon which prevents the fat from adhering to the sides. Hard plastic containers of any kind are also good choices for both refrigeration and freezing. Other milkbags, sold specifically as bottle liners, are not as durable, making them an unacceptable alternative when freezing the milk as the seams may burst during the freezing process perhaps causing a leak during thawing. Also, one study found that there was a 60% decrease in the milk's antibodies and a loss of fat that adhered to the sides of these bags. If this type of bag is still chosen, the milk can be better protected by placing the liner bags in a larger gallon size freezer bag or in a hard plastic container.

When milk freezes it expands, so it is necessary to leave about an inch at the top of the container to allow for expansion. For this reason, bottle caps or container lids should not be tightened until the milk is completely frozen.

Fresh human milk separates into milk and cream, so it is important to gently swirl the container to mix the milk before offering it to your baby.

While it was originally thought that a mother had to cool her fresh breastmilk before combining it with previously expressed cooled milk, the latest research now shows that you may pump directly into already refrigerated or cooled milk as long as the milk is added within 24 hours of the first milk expressed. You should then follow the storage recommendations based upon the time and date of the first milk expressed. You may pump directly into milk that has been stored at room temperature as long as you do so within 10 hours. This milk would need to then be used.

You may add your fresh milk to what you have already frozen as long as you chill the fresh milk first for about half an hour and it is a smaller amount than the amount that you are adding it to.

When thawing milk it is best to thaw it in the refrigerator. This takes about 12 hours. If you need a quicker method you may hold the container under water that is gradually warmed or you may place it in a bowl of water that again is gradually warmed. Another, newer method that affords a faster warm is the Avent bottle warmer. This warmer allows for a gradual warm and has been tested on breastmilk and not shown to affect any of the milk's properties. Regardless of the method of warming you choose, shake the container before testing the temperature. Human milk should NEVER be microwaved or heated directly on the stove! These heating methods alter the composition of the milk and may result in hot spots in the milk that could perhaps burn your baby!

Once thawed, breastmilk should not be refrozen. It also should not be reheated once heated.

It is best to store in portions of 2-4 ounces to avoid less waste. These smaller portions also thaw and warm more quickly.

Extensive research has not yet been done to determine if it is safe to give a baby milk that was left over from a previous feeding or milk that was previously warmed, but not used. However, most lactation experts agree that milk that is not finished at one feeding may be offered at one more feeding before needing to be discarded. Human milk has antibacterial and antimicrobial properties that result in slower spoilage as compared to other foods.

Milk is not spoiled unless it has a sour odor or tastes bad. Some moms find that their milk seems to spoil rather quickly despite careful attention to proper storage and handling. This is thought to be a result of the milk having an excess of lipase, an enzyme which helps break down the fats in human milk. One way to keep milk from spoiling so quickly is to halt the breakdown of fats by scalding the milk just prior to storing it. This is done as soon after expression as possible and over a stove eye. Scalding the milk involves allowing small bubbles to appear on its surface but removing it from the heat before an actual boil occurs. The milk should then be stored immediately either in the refrigerator or freezer.

Other mothers have reported a soapy smell to their frozen milk after it is thawed. This change in smell has been attributed to changes in the milk fats related to storage in self-defrosting refrigerator-freezers. It has not been found to be harmful to the baby.

Sometimes odors from the refrigerator or freezer can enter stored breastmilk. To avoid this, be careful about your choice of storage containers (review the information above), consider adding a box of baking soda to the unit, throw out old leftovers and make sure any newer food is covered or wrapped tightly, and check that the temperature of your refrigerator or freezer is set low enough. .

The appearance of stored milk can take on many forms. Most moms notice that after a while the fats in the milk begin to separate from the body of it. They may rise to the top or settle on the sides of the storage container. Before emptying the milk into your baby's bottle or cup and right before serving it to baby, be sure to gently swirl the milk so that the fats can be redeposited back into the rest of the milk.

Milk that has been expressed can look thin and some moms may think this appearance means that their milk is low in fat. Human milk does not look like cow's milk in its container. Cow's milk has been homogenized giving it a more white appearance than cow's milk that has not been homogenized or expressed human milk. At other times, the milk may take on different tints of color.. This can be in relation to something mom has eaten or a medication she is taking. The color of the milk is not harmful to the baby. And keep in mind that if the milk was not expressed, noone would be any wiser as to its appearance as it left the breast straight into baby's mouth.

Be careful about your source for information concerning storage and handling of breastmilk. It's wise to disregard most information contained in booklets published by formula companies in regards to expressed human milk. Often this information is inconsistent and outdated. It is also not in the best interest of the formula companies for a mother to have plenty of safe, expressed breastmilk on hand should she need to offer her baby a bottle or cup. Other literature, books, etc. offering information on storage and handling should be up-to-date and from an authority on breastfeeding; ie. lactaction consultant, La Leche League, medical professional with expertise in breastfeeding, etc.

Last revision: July 31, 2002

"Common Concerns When Storing Human Milk"