Why Can’t You Add Warm Breast Milk to Cold Milk?

If you’ve ever wondered whether or not it’s ok to add warm breast milk to a cold bottle, this article is for you.

At first glance, the answer might seem obvious: “No way!” But in actuality, there are some scientific reasons why adding warm milk to a baby’s cold bottle can be harmful. For that reason, let me explain how and when warm breast milk should be added into baby bottles.

Why cant you add warm breast milk to cold milk

When you add warm milk to a cold breast milk, the temperature of the breast milk will raise. This can cause bacteria to grow, and make the baby sick.

It’s important to always make sure that the milk is at the same temperature as the baby’s bottle before adding it in.

To combine the two, chill the freshly expressed milk in the refrigerator. Once cool, it can be safely combined with refrigerated breast milk that was pumped the same day.

When mixing milk can be ok

Generally, you will not want to mix warm breast milk with cold milk. But, there can be an exception if you are feeding it to the baby right away.

If you have freshly expressed breast milk and it isn’t as much as your baby typically takes in one feeding, then you can mix warm milk with the cold breast milk since it would be warmed anyway and it is not being stored for later consumption.

How to combine and store

Combining and storing breast milk can be a bit tricky, but with a little know-how, it can be easy. Here are the best ways to combine and store your breast milk. We will also provide tips on how to make the process as smooth as possible.

1. Start by pumping into a clean bottle and put the bottle of breast milk in the refrigerator

2. For your second pump, pour the cold breast milk into a jar. Clean and pump into that bottle.

3. After your second pump has finished, then follow these steps:

4. Go to the refrigerator and put away the milk from your second pump

5. Take the bottle of milk from the first pumping session that has already chilled

6. Pour the chilled milk from the first pumping session into the pitcher

7. Continue combining the chilled milk into the large pitcher as you pump throughout the day

8. Mark a line on your pitcher with how many ounces of breast milk are needed for each day – this is what you should fill it up to each day.

9. Once you have hit your minimum amount, you can place all your extra breast milk straight into the freezer to build up your freezer stash.

baby on couch drinking bottle

Ways to track pumped milk dates

There are a few different ways to track the date that milk is pumped. One way is to use a dry erase marker to write the date on the bottle. The marker can be easily wiped off prior to washing the bottle.

Another way is to write the date on a post-it note, and stick it onto the bottle. The post-it note can be secured with a rubber band if the stickiness of the post-it note is not strong enough to adhere to the bottle.

baby in bouncer drinking bottle

A third way is to use lids with different colors, or bottles of different colors for each day of the week.

Another way is to put the freshest milk in the back of the refrigerator, so the oldest is in the front. When you grab a bottle for feeding, use the bottle from the front.

And lastly, I found that once I had more than about two days worth of stored milk in the refrigerator, it was easiest to freeze all of it. Once in freezer bags, I could write on the label the date the milk was pumped.

You can also keep track of your frozen breast milk with this breast pump log and inventory list.

Can you mix milk from different days?

It is better to mix expressed breast milk from the same day. If you have to mix milk from two different days, put the earlier date on the container. Follow the storage guidelines for that date.

Can you combine milk from each breast?

If you pump both breasts at the same time, it is okay to combine the milk from both breasts into one bottle. This is because the milk in both bottles will be at the same temperature when freshly pumped.

Some mothers choose to combine milk from each breast, while others do not. There are pros and cons to both methods.

Pros of combining milk from each breast:

  • You will have less storage bottles taking up space in your fridge
  • It is easier to track how much milk your baby is consuming

Cons of combining milk from each breast:

  • It may be harder to track what each side is producing

Can you put milk straight into the freezer?

It is best to let freshly pumped milk cool in the fridge before freezing it. This helps the milk freeze correctly. To save time, pour the milk into a freezer bag and label it after pumping. Then move the expressed breast milk into the freezer once it has cooled down. Make sure to use the milk within 3 to 6 months of freezing it.

There are important safety considerations when storing your breastmilk. To ensure food safety, each container should be cleaned before using it to store any type of liquid food, including human breast milk.

This includes washing all surfaces with soapy water and rinsing well with clean water. Then sanitize all surfaces used for handling expressed milk either by boiling them for five minutes or washing them in a dishwasher set on “sanitize.”

Once everything has been washed and sanitized, it is safe to express breast milk and then transfer it into storage bags. Make sure the bottles, pumps, and hands used to collect the breast milk have been properly cleaned as well.

baby bottle on the counter

Use the milk separately

If you can’t make the milk at the same temperature, you can give them the cold milk first. After they finish that, give them the warm milk. If they don’t mind drinking cold milk, or you having to use two bottles, then there’s no problem with doing this.

Risks with combining milk

When you combine milk from different days, you are increasing the risk of bacteria growth. This can cause your baby to become sick.

Additionally, when you mix milk from each breast, you may not be able to track how much milk your pumping on each side.

Finally, when you put milk straight into the freezer, you run the risk of it not freezing correctly.

Preemie babies

If you have a preemie baby, this is especially important to take caution.

-Never combine milk from different days together, this can cause your baby to become sick with bacteria growth.

When pumping fresh breast milk, make sure to always clean the bottles and breast pump parts before doing so.

-Cool freshly expressed milk in the fridge first before storing it into the freezer.

If you are ever worried about issues related to breastfeeding or storage of milk, contact a lactation consultant or talk to your doctor. They will be able to help you with any questions you may have!

newborn baby drinking bottle

Frozen breast milk

There are a few different ways that you can freeze breast milk.

The best way to freeze breast milk is by pouring it into freezer bags. This way, you can easily thaw the milk by placing it in the fridge or under warm water.

It’s important to cool the breast milk in the fridge before freezing it. This is because if you freeze milk that is still warm, the breast milk will freeze at the wrong amount of time.

Make sure to label the freezer bags with the date you pumped the milk. Then move the bagged milk to your freezer once it’s cooled down. Make sure to use the frozen breastmilk within 3 to 6 months of freezing it.

The best way to keep breast milk fresh in your fridge is by storing it in a tightly sealed container like a glass baby bottle or plastic bottle.

Mixing freshly expressed breast milk

When you first start pumping, it is best to refrigerate the freshly expressed breast milk immediately. You can then freeze it later on. It is important to cool the milk down before freezing it. This helps the milk freeze correctly and prevents bacteria growth.

Final thoughts

When it comes to storing breast milk, there are important safety considerations that every mom should know. In this article, we have outlined the best ways to combine and store expressed breast milk. We also discussed the risks of adding warm milk to a cold bottle and why you shouldn’t do this. If you have any questions or concerns, be sure to talk to your doctor or lactation consultant.

Be sure to read The Ultimate List of Breastfeeding Essentials and 10 Must Have Features for the Perfect Breast Pump Bag

About the author

Lacy Reason is a highly experienced and compassionate lactation counselor, who has dedicated her career to educating and supporting new mothers on their breastfeeding journey.