Guidelines for Storing Human Milk

By: Anne Smith

These guidelines apply to milk that will be given to healthy, full-term babies. If you are expressing milk for a sick or premature baby, check with your doctor or hospital staff regarding collecting, handling, and storing your milk.


Human milk can be safely stored in glass, hard plastic bottles, plastic freezer bags, or polyethylene milk storage bags especially designed for storing breast milk.While you have many options for storing your milk, I recommend the CSF bags made by Medela (see product information for details). They are pre-sterilized and lined with nylon that keeps fat cells from adhering to the sides. They are designed to protect the nutrients and anti-infective qualities of human milk. They are thicker than the bottle liners sold for use with disposable bottle systems, which may split during freezing and may cause a decrease in the antibodies and fat which adhere to the sides of the bags. They also take up less room in your freezer, and the milk thaws faster than milk frozen in hard containers. There has been a controversy for years over glass versus plastic containers for human milk. While glass is good for storing frozen milk because it is non-porous, it has disadvantages. The most obvious is that it can break, and you don't want to waste any of your 'liquid gold'. Don't use glass bottles if you are going to store the milk for less than 24 hours, because some of the white blood cells will adhere to the glass, but not to plastic. Since the cells detach after 24 hours, the composition (glass versus plastic) doesn't matter if you are freezing the milk. Since many of the white blood cells are destroyed by freezing, it makes sense to refrigerate milk whenever you will be using it within 8 days, and use CSF bags especially designed for storing human milk when you must freeze it. They protect the immune factors as well or better than glass, they don't break, they take up less room in your freezer, and they thaw out faster. Plus, they are easier to find. Have you tried to buy glass bottles lately?

You may want to freeze your milk in ice cube trays. Clean the tray first with hot soapy water and air dry. Each cube is about an ounce, so you can pop out as many ounces as you want and put them into freezer bags. They are great to have on hand for snack or cereal feedings when you just need an extra ounce or two.

When storing milk in bottles, wash them in hot soapy water and air dry. Choose a top that fits well. You can boil them if you want to, but it isn't really necessary. CSF bags are sterile and don't require any preparation before use.

When milk is frozen, it expands, so leave about an inch at the top of the container to allow room for expansion.

Put only two to four ounces of milk in each container, or the amount your baby will take at a single feeding. Smaller quantities are easier to thaw, and you avoid waste this way. It's always good to have some smaller amounts on hand for snack feedings, or to offer if your baby finishes one feeding and is still hungry. You can add fresh milk to a container of frozen milk as long as there is less fresh milk than frozen. Cool the milk for 30 minutes first. For example, you can add 2oz. of fresh milk to 4oz. of frozen, but not 4oz. of fresh milk to 2oz. or frozen. You don't want it to thaw and then refreeze.

Label each container with the date it was expressed. If you are taking it to day care, put your baby's name on the label. Medela's CSF bags have a label area that stays flat even when the bag is full. Since the composition of human milk changes to meet your baby's needs as he grows, always use the freshest milk possible.

Storing Human Milk

Whenever it is possible, give your baby fresh milk that has been refrigerated, not frozen. Freezing kills some of the live cells and antibodies in human milk, but not all of them. Since formula doesn't have any of these anti-infective properties to begin with, frozen milk is still better for him than formula. If you are planning to use the milk within eight days, refrigerate it rather than freezing it.

Because human milk is a living substance, its antibacterial properties help it stay fresh longer than formula. How long you can store it depends on the temperature.

.With all these guidelines, remember that fresh milk which has been stored at room temperature or in a cooler before being placed in the fridge or freezer may not keep as long. That's why you should always place milk in the fridge as soon as possible after expressing it.

New research indicates that milk that has been offered to a baby but has not been heated can be kept at room temperature for up to 4 hours, or 24 hours if you put it in the fridge right away. Once the milk has been heated, it can sit at room temperature for up to 2 hours, but then should be discarded. Milk that has been heated and offered to the baby can be refrigerated within 30 minutes and offered again for the next feeding, but discarded after that. These are the guidelines I've suggested to mothers for over 10 years, and have never heard of any problems.

When a refrigerator isn't available, put the milk in an insulated container with icepacks. The PumpInStyle comes with it's own built-in insulated container and icepacks, making it ideal for transporting milk home from work.

Handling and Thawing

Human milk may separate into layers of milk and cream during storage. Gently shake it to mix the fat that has separated.

Breastmilk may look bluish, greenish, yellowish, or brownish according to what you have eaten recently. Foremilk expresses at the beginning of a pumping session may look thinner and bluish, like skim milk. Hindmilk expressed later in the feeding may look thicker or creamier, and have a yellow tint. The yellow tint is especially pronounced during the first week or so of nursing while the milk still contains colostrum. Your milk may smell 'soapy' after it is frozen and then thawed. This is due to changes that occur during the freezing process, and is not harmful to the baby. Breastmilk isn't spoiled unless it smells really bad or tastes sour.

You can pump directly into refrigerated milk as long as you add the milk within 24 hours of when the original milk was expressed. If milk has been stored at room temperature, you can pump directly into it as long as you do it within eight-ten hours. You then need to use the milk as soon as possible.

If you plan to use the milk within 8 days, don't freeze it. If you do plan to freeze it, do so within 24-48 hours of expressing it. The sooner you freeze it, the better.

To defrost frozen milk, place it in the fridge the night before you're going to use it. This takes about twelve hours. If you need to thaw it quickly, run it under warm water that is gradually warmed, or place it in a bowl of water that is gradually warmed. Don't use hot water, and never heat it in a microwave. This can destroy the live antibodies in the milk, and may also create 'hot spots' than can burn your baby's mouth, even though the container may not feel hot to the touch.

Many babies don't care if the milk is served cold right out of the fridge. It won't upset their stomach, and will save you or your caregiver a minute or two, which can be really important if your baby is frantically hungry. If you want to try cold milk, be sure to run the nipple under warm water if it has been refrigerated. Most babies dislike cold nipples more than they dislike cold milk.

How Much Milk to Leave for Your Baby

Average intake by age:

Average intake by weight: The average baby who isn't eating anything but milk needs about two and a half ounces per pound of weight. Some babies need more, some need less in order to gain weight adequately. A ten-pound baby needs about 25 ounces in twenty-four hours (round up an ounce or two to be on the safe side — say 27 ounces) which means that if he eats eight times in 24 hours, he would need a little over three ounces at each feeding. You'll get a feel for how much he will eat at each feeding as he begins to take bottles on a regular basis.

FYI: Human milk is not considered a bio-hazardous body fluid like blood or saliva, and OSHA and the CDC agree that it does not have to be treated as such. For more details on handling breastmilk in a work or day care setting, see the article on "Returning to Work or School". The article "The Caregiver's Guide to the Breastfed Baby" gives concise information on handling human milk that you can share with your baby's care provider.

Anne Smith is an IBCLCInternational Board Certified Lactation Consultant and La Leche Leader since 1978. More importantly, she is a mother to 6 breast fed kids with twenty plus years experience of counseling nursing mothers. Her site,, provides expert advice and solutions to breast-feeding problems and gives basic information on how to breast feed. Anne also features her recommended breast feeding products and breast pumps.

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