Adding Fresh Breast Milk to Refrigerated: Safety Guidelines

| Reviewed By Sarah Schulze, MSN, APRN, CPNP

If you are either exclusively pumping or using pumping to supplement breastfeeding, you have the option to store newly expressed breast milk in the refrigerator or freezer. But, what is the protocol when it comes to combining fresh milk with already refrigerated milk?

Can you add warm milk to cold milk? No, you cannot add warm breast milk to refrigerated breast milk. It’s best to first refrigerate freshly expressed milk to make it the same temperature as the refrigerated breast milk you already have. You should also use all the mixed milk within four days of expressing the oldest batch of milk.

Read on to learn more about storing your breast milk in the fridge safely.

Breast Milk Storage in Fridge

If you don’t plan on using freshly expressed milk right away, you can store it in the fridge.

Here’s what you need to know about storing breast milk in the refrigerator.

Why You Should Not Add Warm Breast Milk to Cold Milk

Adding warm breast milk to cold milk can rewarm the refrigerated milk. Rewarming refrigerated breast milk is generally safe for most healthy, full-term babies.

However, if your baby has a medical condition or was born pre-term, there’s a chance the bacteria from rewarmed breast milk can harm your child.

Breast Milk Storage Temperature

According to the Office on Women’s Health, you can store breast milk at the following temperatures:

  • Room temperature: Up to 77 degrees Fahrenheit for up to four hours
  • Refrigerated: Store at 40℉ for up to four days
  • Freezer: Store at 0℉ or cooler for up to six months

Adding Fresh Breast Milk to Refrigerated Breast Milk Safely

If you want to add fresh breast milk to refrigerated breast milk safely and have a healthy baby, make sure you cool the freshly expressed breast milk in the refrigerator before mixing it with the cold milk.

Keeping both batches of milk at the same temperature reduces any possible contamination.

Accidentally Mixed Fresh Breast Milk With Refrigerated

Cool fresh breast milk in the refrigerator before mixing it with cold milk to keep them at the same temperature.

If you accidentally mix fresh breast milk with refrigerated breast milk, the new batch can rewarm the cold milk. There are no known risks to rewarming refrigerated milk for healthy babies.

Combining Breast Milk From Different Days

If you’re combining breast milk from different days, make sure the oldest milk is fewer than four days old.

When you store the breast milk, always label it with the date you expressed the oldest milk. Then, use the milk within four days of the oldest milk you pumped.

How Long Can Breast Milk Last in the Fridge?

Breast milk can last in the fridge for up to four days. It’s best to use breast milk as soon as possible.

Breast milk has qualities that slow the growth of bacteria, but those qualities decline after a few days. If you know you won’t use the breast milk within a few days, freeze it immediately.

How Long Can Breast Milk Stay Out of the Fridge?

Breast milk can stay out of the fridge at room temperature for up to four hours, preferably in a sealed container.

If you thaw frozen breast milk, it can sit at room temperature for about one or two hours. If your baby starts eating the milk, it can sit at room temperature for up to two hours.

Can Warmed Breast Milk Be Refrigerated Again?

Yes, warmed breast milk can be refrigerated again as long as your baby didn’t drink from it.

Once your baby has drank from the bottle of milk, you should feed any remaining milk within two hours. It’s best to avoid wasting breast milk by offering your baby a small amount at a time.

Can You Freeze Refrigerated Breast Milk?

Yes, you can freeze refrigerated breast milk, but you should freeze it as soon as you’re confident you won’t use the milk in the next few days.

Breast milk only lasts about four days in the refrigerator. It’s best to freeze freshly expressed breast milk to keep your baby safe from bacteria.

How To Store Breast Milk After Pumping

Follow these tips for storing breast milk after pumping:

  • Store milk at room temperature for up to four hours.
  • Store milk in the refrigerator for up to four days.
  • Store milk in the freezer immediately after pumping for up to six months.
  • Store milk in an insulated cooler pack or cooler with frozen ice packs immediately after pumping for up to 24 hours. Refrigerate or freeze your breast milk within 24 hours of storing it in an insulated cooler pack or cooler.
  • Store milk in breastmilk storage bags, hard BPA-free plastic bottles, or clean glass bottles with tight-fitting lids.

How To Use Breast Milk Storage Bags

Breast milk storage bags (these hygienic, double-sealed bags come highly recommended) help you keep and organize pumped breast milk without taking up too much space in your fridge or freezer.

  1. To use these bags, pour your freshly expressed breast milk into the bag.
  2. After sealing the bag, write the time, date, and amount on it before you put it into the freezer or fridge.
  3. Depending on the kind you get, the bags will most likely be able to stand up on their own, so you can easily fill them and store them upright.

How To Warm Breast Milk From Fridge

Depending on your baby’s preference, you might not need to warm breast milk from the fridge.

If your baby likes warm milk, follow these steps to get breast milk to the right temperature:

  • Keep the milk storage bag or container sealed.
  • Put the milk container or storage bag into a bowl of warm water. You can also run the bag under warm water from the sink for a few minutes.
  • Before feeding your baby, test the temperature of the milk by pouring a little on your wrist.
  • Avoid putting milk in the microwave, which can eliminate some of the milk’s nutrients.

Related Questions:

Can I Add Fresh Breast Milk to Room Temperature Breast Milk?

Yes, you can add fresh breast milk to room-temperature breast milk. Any milk you mix together should be at the same temperature.

Keep in mind that your baby needs to consume room-temperature breast milk within four hours of expression, especially if the temperature in the room is warm.

Does Frozen Breast Milk Taste Different?

Yes, frozen breast milk tastes different. Studies show that frozen breast milk may be more rancid than freshly expressed milk.

If your baby refuses to drink thawed breast milk, you may want to substitute it with freshly expressed milk or only freeze your milk for fewer than seven days.


When adding fresh breast milk to refrigerated breast milk, practice the recommended safety guidelines to protect the milk’s nutrients and keep your baby healthy.