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Christin Perry

The Dos and Don’ts of Breast Milk Storage

You’ve worked hard to collect that milk, so don’t waste a drop! Here’s how to store breast milk safely in the fridge and freezer.

Whether you’re heading back to work or just looking to have bottles on hand, pumping is a great way to stock up on breast milk. But how should you go about storing breast milk? What container you use, where you place it, what temperature you keep it at and how long you store it can all impact how safe and nutritious your milk is for baby. Being smart about breast milk storage is no doubt a science—but don’t worry, we’ve made it easy. Read on to learn how best to preserve the fruits of your labor.

In this article:
Breast milk storage guidelines
How to store breast milk
How to thaw frozen breast milk
How to warm breast milk
How to tell when breast milk has gone bad

Breast Milk Storage Guidelines at a Glance

Breast milk is like liquid gold, so it’s understandable to want to make use of every ounce you pump. Which brings us to the million dollar question: How long is breast milk good for? When storing breast milk, keeping it fresh is key. To properly store breast milk and protect it from spoiling, check out The Bump chart of breast milk storage guidelines below, which explains the details of how to store breast milk, including how long and at what temperature.

Keep in mind that this guide, based on information from the Centers for Disease Control and Prevention (CDC), should be used only for healthy, full-term infants. Talk to your pediatrician about storing breast milk for premature infants, since these babies have much more sensitive immune systems.

Here are some important breast milk storage tips to always keep in mind:

• On the counter: Store breast milk in the coolest place you can find, away from direct sunlight. Don’t store breast milk for any amount of time at temps higher than 77º F due to the risk of bacteria growth.

• In a cooler bag: You can safely store breast milk in a cooler for up to 24 hours. Keep ice packs on the milk container at all times, and don’t open the cooler bag until you absolutely have to.

• In the fridge: Store breast milk in the center of the fridge, as far back as possible. Don’t store it in the fridge door, where temperatures vary widely.

• In the freezer: Store breast milk in the back of the freezer, where temperatures are more consistent. Place it in sealed containers or breast milk storage bags, and always use the oldest milk first.

How to Store Breast Milk: The Details

When it comes to storing breast milk, remember this simple rule: Use the fridge for short-term breast milk storage and the freezer for long-term storage. Breast milk will stay fresh for many months in the freezer, as long as it’s stored properly, but it won’t be as nutritious for baby as the fresh stuff, since freezing breast milk kills off some of its natural vitamins, including important antioxidants. Refrigerated breast milk retains its nutritional quality better than frozen (though it will spoil more quickly), and the only thing better is freshly pumped milk. Still, there are merits to storing breast milk in the freezer or the fridge. Read on for the 411 on freezing breast milk vs. storing breast milk in the fridge.

How to store breast milk in the fridge

If you’re planning to use your expressed milk pretty soon, keep it in the refrigerator so you don’t have to worry about thawing it. But how long can breast milk stay in the fridge? The refrigerator should be thought of as a short-term breast milk storage solution: It’s best to use refrigerated breast milk within 24 hours, though properly stored milk can last as long as four days. Here’s the scoop on how to store breast milk in the fridge:

• Start with the right container. When storing breast milk, use a clean container, such as screw-cap bottles, hard plastic cups with tight caps or heavy-duty breast milk storage bags. “Make sure the bags aren’t filled past the measurement indicator line, seal the bag tightly and place in a food storage container to keep it away from meats [and other uncooked foods to avoid contamination],” says Tamara Hawkins, FNP, RN, IBCLC, director of Stork & Cradle, a lactation consultancy in New York City. What’s not recommended are regular plastic storage bags, since they can easily leak or spill.

• Location, location, location. The real estate you carve out for breast milk storage matters, especially in the refrigerator. Always place freshly pumped milk in the back of the fridge, since this is the coldest area. The door, where temperatures fluctuate every time it’s opened or closed, is the worst place for storing breast milk in the fridge.

• It’s okay to mix milk from several pumping sessions. Sometimes you just don’t get enough milk from a single pumping session, leading many moms to wonder: Can you add fresh breast milk to refrigerated breast milk? Answer: Yes, it’s okay to combine pumped milk from several sessions, with a caveat: Always chill the new milk before adding to the old. “When you mix milks that are two different temperatures—for example, combining a bottle in the fridge with freshly pumped milk and then putting it back in the fridge—the cold milk will get warmer, then colder again, and then rewarmed when given to baby,” says Regina Eichenberger, PA-C, IBCLC, a board-certified lactation consultant in Stratford, CT. A better idea is to combine the milks once they’ve both been sitting in the fridge for a few hours. If you won’t be using the milk immediately, label it using the date of the older milk and move it to the freezer. Note that it’s never safe to add fresh breast milk to frozen breast milk. “The fresh milk, since it’s warmer, may actually thaw some of the frozen milk, which may lead to storing spoiled milk,” says Nancy Clark, IBCLC, director of Northern Virginia Lactation Consultants in Gainesville, VA.

• Don’t reheat already-warmed milk. “Breast milk should be warmed only once,” Eichenberger says. “Rewarming breast milk more than once increases the risk of bacteria growth.” Your best bet? Serve any unused milk at the very next feeding, and serve it chilled rather than rewarming it.

How to freeze breast milk

As you start to build up a stash, you’ll need to claim some real estate in the freezer for breast milk storage. Especially if you don’t think you’ll use your freshly pumped breast milk within four days, freezing breast milk is a smart way to better preserve the nutrients. So how long does breast milk last in the freezer? According to CDC guidelines, breast milk can be stored in the freezer for up to a maximum of 12 months, although it’s best to use the milk within 6 months. Here are some important tips for freezing breast milk to ensure it stays safe for baby:

• Consider your container. Like fridge storage, knowing how to freeze breast milk starts with using the right container. For long-term breast milk freezer storage, use a glass or BPA-free plastic container that seals tightly and is freezer-grade. That can include glass jars with screw caps or hard plastic containers with snap tops. Breast milk storage bags can be used for freezer storage but won’t keep milk protected for as long as sealed containers. “The bag may leak or spill and can become contaminated more easily than a hard container,” Hawkins says. Leave an inch of space at the top, since breast milk expands when frozen.

• Store milk in small batches and label it clearly. Just like any food, once breast milk is thawed, it can’t be refrozen. To avoid wasting unused milk, store milk in small batches of 2 to 4 ounces and label with the date. It’s easy to heat up more milk if baby is still hungry, but keep in mind that if baby only drinks part of a bottle of thawed milk, you can only store the remaining milk for about an hour or two in the fridge before discarding, and it should never be rewarmed.

• Store where the temperature is most constant. “Be smart about where you place the milk. In the back center of the freezer, temperatures will be the coldest and most constant,” Eichenberger says. “Avoid putting milk in the freezer door. Since the door is constantly being opened and closed, the temperature is more likely to be variable.”

How to Thaw Frozen Breast Milk

After freezing breast milk, you’ve got to reheat it once you’re ready to use it. Wondering how to thaw frozen breast milk? We’ve got you covered.

There are several ways to go about defrosting breast milk, and the microwave isn’t one of them. “Doing so can kill all the breast milk’s living immune properties and create hot spots that can potentially burn baby's mouth or throat,” Hawkins says. The best way to thaw frozen breast milk is to leave it in the refrigerator overnight. “If a rush defrost is needed, place the container of breast milk in a bowl of warm water, making sure the water doesn’t rise above the rim of the bottle,” Hawkins says. Admittedly, defrosting frozen breast milk can be time consuming, so plan ahead and always keep some breast milk in the fridge to have on hand.

Wondering how to store thawed breast milk? If you’re not feeding baby immediately, keep it in the fridge. If you thawed it at room temperature, the milk is good for up to two hours (after that, throw it out); if you thawed it in the fridge, it can be used for up to 24 hours.

How to Warm Breast Milk

The last thing you want to do when baby is howling to be fed is wait for milk to warm up—but it’s quicker than you think! Gently swirl (if it’s in a bottle) or massage (if it’s in a bag) the milk while you hold it under warm, running water for several minutes. You can also fill a bowl with warm water and let the milk heat up. Just be sure to use warm water, not hot, so the milk doesn’t overheat. Another option for how to warm breast milk is to use a bottle warmer. Again, stay away from the microwave—the uneven heating could easily scald a baby or damage the milk, Clark says. Regardless of the method you choose, always make sure the milk is just the right temperature for baby; test a drop on the inside of your forearm—it should feel warm, not hot.

How to Tell When Breast Milk Has Gone Bad

As eager as you may be to use up all your pumped breast milk, you also want to be sure the milk you feed baby is fresh and safe to drink. So how can you spot spoiled breast milk? There are a few simple ways.

First, examine its appearance. When chilled, your breast milk will naturally separate into layers, with the fat rising to the top. The milk should easily mix after you swirl it around; if you still see separated clumps, it could be a sign your milk has gone bad. “You’ll know if the milk is absolutely bad because it’ll appear stringy, mucusy or will look as though there’s pus in the milk,” Hawkins explains.

You can also give the milk in question a smell. Spoiled milk will have that rancid, foul odor that’s hard to mistake, similar to cow’s milk that’s past its prime. Still not sure? Perhaps the easiest way to detect spoiled breast milk is to taste it, Hawkins adds. Spoiled breast milk will have that unmistakable sour taste.

Lipase in breast milk

Occasionally, mother nature throws us a curveball. Some moms may detect a sour or soapy smell from their breast milk after its been stored in the fridge or freezer—but it doesn’t mean the milk has gone bad, Hawkins says. It could simply be a sign that your milk has high levels of lipase, an enzyme that helps baby easily digest the fat in your breast milk and absorb essential fatty acids like DHA.

Having a lot of lipase in breast milk isn’t necessarily a problem. “Many babies are unbothered by this,” Hawkins says. “They drink the milk without any hesitation and there’s nothing to worry about. The milk is still good.” But other babies might not appreciate the odor and refuse to drink your milk after its been stored. Take heart! Scalding or heating freshly pumped milk to a high temperature can tamp down on the lipase activity and get rid of that sour or soapy smell.

When scalding breast milk, place it on the stove (never the microwave) and keep a careful eye on it—you don’t want the milk to reach a boil, Hawkins cautions. Instead, you’re aiming to heat the milk to 144 F for one minute. You can use a food thermometer to know when you’ve reached the right temp, or simply keep the milk over heat until you spot small bubbles rising along the edges of the pan. Once the milk is ready, take the pan off the stove and sit it in a bowl of ice water to cool down rapidly. You can then store your cooled milk as you would normally.

Updated August 2018

Plus, more from The Bump:

Pumping 101: How to Pump Breast Milk

21 Pumping Tips to Get You Through the Day

Don't Waste a Drop: The Best Breast Milk Storage Bags