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Common Concerns When Storing Human Milk

by Cindy Scott Duke

(from "Keeping Abreast" July-September 1999 issue)
From: NEW BEGINNINGS, Vol. 15 No. 4, July - August 1998, p. 109, [Reprinted with permission from La Leche League International

One of the many benefits of breastfeeding is convenience. Most of the time, human milk goes directly from producer to consumer, with no concerns about collection, storage, preparation, or freshness in between. However, some mothers express and save milk for their babies, either occasionally or regularly. This article addresses some common questions and concerns about the appearance of expressed milk and safe storage of  human milk for healthy, full-term babies. If your baby is hospitalized or you are collecting milk for a milk bank, different guidelines may apply.

Visual characteristics of human milk
Those who have never seen human milk may be surprised if they expect it to look like cow's milk out of a carton. Unlike homogenized milk, human milk will separate when left to stand, with the fat rising to the top. This does not mean it has spoiled. Simply shaking the container gently will restore the milk to a homogeneous consistency.

Samples of human milk expressed at different times may not look the same either, as various factors can influence  fat content and even color. The amount of fat can fluctuate from day to day and within a nursing or pumping session as well. Milk expressed at the beginning of a feeding may look "thinner" than milk expressed later, when the milk ejection reflex sends milk higher in fat toward the nipple.

The color of human milk can vary. Colostrum is generally yellow to yellow- orange. The transition from colostrum to mature milk can take about two weeks to complete. During that time, the color changes gradually to a bluish white color. However, the color of mature milk may change because of mother's diet or medications. Food dyes used in carbonated sodas, fruit drinks, and gelatin desserts have been associated with milk that is pink or pinkish orange. Greenish milk has been linked to consuming green- colored sports beverages, seaweed, or large amounts of green vegetables. One woman consuming a certain prescription medication reported black milk. Frozen milk may look yellowish.

Pinkish milk may indicate blood in the milk. This could occur with or without cracked nipples. If cracked nipples are the cause of blood in the milk, a mother can contact a La Leche League Leader for suggestions on healing sore nipples. Blood in milk is not harmful to babies, and breastfeeding can continue. If blood in the milk does not cease by two weeks postpartum, the mother may wish to consult with her health care provider.

Odor of human milk
Under most circumstances, fresh human milk has a mild, slightly sweet scent. Occasionally, human milk that has been frozen and thawed may smell soapy and may be rejected by the baby. In "Breastfeeding: A Guide for the Medical Profession", Ruth Lawrence, MD, postulates that for some mothers, milk stored in a self- defrosting  freezer may have had changes in its lipid structure due to the freeze-thaw cycles that occur in such freezers.

In a few cases, mothers have reported that their milk began to smell soapy as soon as it cooled, regardless of whether it had been frozen. "When these mothers heated their milk to a scald (not boiling) and then quickly cooled and froze it," writes Lawrence, "the effect was not apparent and their infants accepted the heat treated milk. That process inactivated the lipase (fat-digesting enzyme) and halted the process of fat digestion."   However, high heating may lower some nutrient levels, including ascorbic acid (vitamin C). If the milk already smells sour, heating will have no effect on flavor or smell. Milk that smells rancid likely is, and should be discarded.

Choosing a milk storage container
After expressing milk into a clean container, milk should be stored in a tightly closed glass or plastic container. There have been controversies about what type of container will best protect the nutrients and immunity factors in human milk. Current research suggests that human milk can safely be stored in glass or plastic receptacles with no significant nutrient loss. THE BREASTFEEDING ANSWER BOOK recommends glass, clear hard plastic (polycarbonate), and cloudy hard plastic (polypropylene), in that order, as storage containers for freezing milk. If a baby receives expressed milk only occasionally, any possible effect of the container on the quality of the milk will be negligible.

Ease of use can be an important consideration when choosing a container. Plastic bags take up less room and can be connected directly to some breast pumps. Bags designed specifically for storing human milk are constructed of thicker material, are easily sealable, pre-sterilized, and have space to label the milk with the date and baby's name. One brand, Egnell Freezer Milk Bags, is available through the LLLI Catalogue. (No.426, $7.95). Disposable polyethylene bottle liners are not designed to store milk and are not recommended. The seams may burst during freezing, and the bag can leak during thawing. If you must use these, double bagging can help avoid tearing. These bags are not recommended for long-term storage.

Cooled milk can be combined with other cooled or frozen milk as long as the quantity of cooled milk is small enough that it doesn't thaw a frozen batch. Freezing milk in small quantities (2 to 4 oz. or 60-120 ml.) helps avoid wasting this precious fluid. Label with the date and your baby's name if it will be stored with milk for more than one baby.

Short-term storage when refrigeration is not available
Lack of immediate access to refrigeration need not be a deterrent to expressing and storing human milk or dampen a mother's determination to continue breastfeeding if she returns to work. Research shows that human milk has an amazing capacity to resist bacterial growth, and can be kept at room temperature for up to ten hours. In a landmark study, mature human milk was expressed into clean, not sterile, containers, some stored at  room temperature (19-22o C or 66 to 72o F) and some refrigerated for ten hours. The milk was then cultured to evaluate bacterial formation. No statistically significant difference was found between levels of bacteria in the milk that had been refrigerated and the milk stored at room temperature (Barger and Bull 1987).

Small coolers, some designed especially for human milk, and wide-mouthed insulated bottles can be used to keep milk cool when electric refrigeration is unavailable. An insulated bottle can be filled with ice before leaving the house to keep the interior chilled. The ice should be emptied just before pouring expressed milk into the bottle.

How long will the milk be "good"? The chart shows storage guidelines based on current research. If your milk will be fed to your baby by someone other than you, you may find it helpful to provide them with a copy of the guidelines.

Milk to be used within eight days of expression should be refrigerated rather than frozen. Not only will the milk  not need to be thawed, but the immunity factors in human milk are better preserved by refrigeration. For longer storage, milk can be frozen.

Keep in mind that the composition of the mother's milk corresponds to the developmental needs of her baby at the time the milk was produced, and try to use the freshest milk possible.

Storing milk away from home
A lactating mother should face no restrictions storing her milk somewhere other than her own home, such as a workplace or day-care refrigerator. No special precautions apply. If an employed mother does encounter resistance from co-workers, it may be lessened if the milk is placed in an opaque, secondary container, suggests Laurie Nommsen- Rivers in the Journal of Human Lactation (1997). There are several sources of information a mother can use to educate others not only about the benefits of human milk but to alleviate any concerns they may have about safe storage of a "body fluid."

In an Oct. 1995 press release, the Center for Breastfeeding Information at LLLI stated, "As of this date, human milk is not (nor has it ever been) included in federal health agencies' listings of body fluids governed by universal precautions for blood borne pathogens which would mandate handling and feeding with rubber gloves or storage in a separate refrigerator as a biohazardous material. This continues to be the current policy of the United States Centers for Disease Control and Prevention (CDC) and the Occupational Safety and Health Administration (OSHA)."  Other countries have considered the idea of universal precautions, however, "specifics regarding breast milk are hard to find," according to Nommsen-Rivers.

"Caring for Our Children," a 1992 joint publication by the American Academy of Pediatrics  and the American Public Health Association (with input from the Human Milk Banking  Association  of North America),  offers guidelines for out-of-home child care programs. This work recognizes, supports, and promotes the feeding of human milk to infants in day care and places no restrictions beyond regular hand washing and standard refrigeration protocols. "Caring for Our Children" is available from: AAP Publications Dept, P.0. Box 927, Elk Grove Village IL 60009-0927. Phone: 800-433-9016; FAX: 708-228-1281.

Mothers who are separated from their babies may have many other questions and concerns beyond milk storage, including easing separation for both mother and baby, pumps and pumping, manual (hand) expression, or making a return to work easier. THE WOMANLY ART OF BREASTFEEDING and LLL Leaders can be valuable resources for these considerations.

Human Milk Storage Information
This information is based on current research and applies to mothers who:
have healthy full-term babies;
are storing their milk for home use (as opposed to hospital use);
wash their hands before expressing;
and use containers that have been washed in hot, soapy water and rinsed.

All milk should be dated before storing.

Storage Guidelines:
Term Colostrum (expressed within 6 days of delivery)
kept at room temperature 27-32 C (80.6-89.6 F)  - 12 hours

Mature milk
kept at 15 C (59-60 F) - 24 hours
kept at 19-22 C (66-72 F) - 10 hours
kept at 25 C (79 F) - 4-6 hours
refrigerated 0-4 C (32-39 F) - 8 days

Frozen milk
freezer compartment located inside a refrigerator - 2 weeks
separate door refrigerator/freezer - 3 or 4 months
(temperature varies because the door opens frequently)
separate deep freeze at constant -19 C (0 F) - 6 months or longer

What Type of Container to Use
If the milk will be frozen;

heavy plastic or glass containers can be used
freezer milk bags are available that are designed for storing human milk
disposable bottle liners are not recommended
cool milk in refrigerator before adding to a container of frozen milk

How to Warm the Milk
Thaw and/or heat under warm, running water; do not bring temperature of milk to boiling point; shake before testing the temperature; do not use a microwave oven to heat human milk.

Thawed milk
If milk has been frozen and thawed, it can be refrigerated up to 24 hours for later use.  It should not be refrozen.

Barger, J. and Bull, P. A comparison of the bacterial composition of breast milk stored at room temperature and stored in the refrigerator. Intl J Childbirth Ed, 1987: 2:29- 30.

Nommsen-Rivers, L. Universal precautions are not needed for health care workers handling breast milk. J Hum Lact. l997; 13(4):267-68.

"Information Please" is edited by LLL Leader Cindy Scott Duke of Davis, CA. She has two children, Amanda (14) and Charlie (5), and serves as the Area Communications Coordinator for LLL of Northern California and Hawaii.

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