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Can I Combine Warm Breast Milk With Cold?

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When I started pumping, I thought it would be really useful if I could combine freshly pumped breast milk with cold milk that was in the refrigerator. I did some research to find the answer.

So, can you combine warm breast milk with cold breast milk? No, you shouldn’t combine warm and cold breast milk. Adding warm milk to cold will raise the temperature of the milk, potentially allowing bacteria to grow. To combine the two, chill the fresh milk in the refrigerator. Once cool, it can be safely combined with chilled milk pumped the same day.

Although this answer seemed to make life a little more difficult, I eventually found the best process to combine and store milk. I also discovered a few tips to combine milk that made the process of pumping and storing milk much easier.

Process To Combine And Store Milk

One method to combine and store milk is to start with pumping into a clean bottle. Have several bottles that you feed your baby from clean and ready to go. As you pump, fill the bottles for each feed.

For example, if your baby eats 4 ounce bottles, seven times per day, then start filling the feeding bottles to the 4 ounce line.

  • If you pump 6 ounces during your first pump of the day, fill the first bottle to 4 ounces.
    • Fill the second bottle with the remaining 2 ounces.
  • During your second pump of the day, you pump 6 ounces again.
    • Fill a third, new bottle to 4 ounces.
    • Then, chill the remaining 2 ounces before combining it with the previously chilled 2 ounces from your first pump.
  • Now you have bottles for 3 feeds ready to go. Once you have seven full bottles, you are an entire day’s worth of feeds ahead of your little one.

If you get ahead, you can start filling bottles for the following day. As you pump, be sure to track the date that the milk was pumped. I have some more information on keeping track of the date your milk was pumped below.

An Alternate Method – Use “The Pitcher” Method To Combine And Store Milk

The pitcher method is useful once you already have a current day’s worth of bottles ready for your little one. This method is popular because it can save the number of bottles that get dirty and you will need to clean at the end of the day.

Start by pumping into a clean bottle and put it in the refrigerator. During your second pump, also pump into a clean bottle. After your second pump has finished, then follow these steps:

  • Go to the refrigerator and put away the milk from your second pump.
  • Take the bottle milk from the first pumping session that has already chilled.
  • Then, pour the chilled milk from the first pumping session into the pitcher.
  • Continue combining the chilled milk into the large pitcher as you pump throughout the day.

Mark a line on the pitcher with the number of ounces your baby eats in a day. This is the line that you will want to fill your pitcher up to each day.

For example, if you are nursing and pumping for the 9 hours when you are at work, then you may need enough milk for 3 bottles at daycare. Your fill line on the pitcher might be at 18 ounces if your son or daughter drinks 6 ounces per bottle.

If you are exclusively pumping, meaning that you are pumping for every feed that your little one eats during the day, then you may need a larger pitcher. In this example, your fill line on the pitcher may be anywhere from the 24 to 30 ounce mark.

Once the pitcher is full up to your fill line, freeze the rest of the milk that you pump that day. This will make sure that the milk in your freezer is as fresh as possible. It will also save space in your refrigerator so it doesn’t continue filling up with bottles of milk.

At the end of the day, stir the milk in the pitcher to keep the fat from separating. Then, pour bottles for your little one’s feeds for the following day. Finally, wash the pitcher so it will be ready to be filled up during your pumping sessions the following day.

When I discovered the pitcher method, it cleaned up the clutter of bottles in my refrigerator. It also saved me time because I was only searching and filling bottles once per day. I searched for a pitcher that was BPA free and safe for infants. Here is a link to the pitcher that I use.

Caveat To Mixing Warm And Cold Milk

In general, you never want to mix warm and cold milk. One caveat to this rule is if you plan to feed the milk immediately after pumping. If you do not plan to put the freshly pumped milk into the refrigerator, then it is ok to top off the bottle with cold milk. This is only because the bottle is for a feeding your baby will take immediately.

This may be the case when you only pump 2 ounces during a pump session, but your baby will usually eat 4 ounces during a feeding. If your baby eats 4 ounces, you can pull 2 ounces out of the refrigerator, top off the bottle with 2 ounces of milk that you freshly pumped, and then place the 4 ounce bottle in the bottle warmer.

In this example where you pumped less milk that your little one takes in a feeding, you would likely be warming up cold milk. Because you are warming the bottle, it is ok to add it to warm freshly pumped milk and then give that bottle to the baby immediately.

Why is it unsafe to combine warm and cold milk?

When pumping milk it is important to understand the reason why it is unsafe to combine milk of different temperatures. Freshly pumped milk is the same temperature as your body, around 98.6 degrees. Cold milk is the temperature of your refrigerator. This is around 38 to 40 degrees for safe food storage.

When warm and cold milk is combined, it raises the temperature of the cold milk above 40 degrees. This potentially creates an environment for bacteria to grow. Young babies are more susceptible to getting sick from bacteria that could grow in the refrigerator. This is because they do not have developed immune systems like older children and adults. To help prevent your little one from being exposed to this potential bacteria growth, avoid combining warm and cold milk from pumping,.

Methods To Track The Pumped Date Of Milk

As you start pumping and storing milk in the refrigerator and freezer, it is important to track the date that the milk was pumped. A few alternatives to tracking the date include:

  • Write the date with a dry erase marker on bottles. The dry erase marker can be easily wiped off prior to washing the bottles.
  • Write the date on a post-it note, and stick it onto the bottle. You can secure the post-it note with a rubber band if the stickiness of the post-it note is not strong enough to adhere to the bottle.
  • Use lids with different colors, or bottles of different colors for each day of the week.
  • 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.

Another tip which helped me out was to only keep enough milk in the refrigerator for the current day and the next day. Once I had more than that, it was easiest to freeze the excess milk. Once in freezer bags, I could write on the label the date the milk was pumped.

Related Questions

Can I mix breast milk from two different days?

It is preferred to mix breast milk pumped during the same day. If there is a reason to mix milk from two different days, then label the milk with the earlier date. Follow storage guidelines based on the earlier date.

Can you combine breast milk from both breasts?

If you pump both the left and right breasts during a single pumping session, it is alright to combine milk from both breasts into the same bottle. This is because the milk in both bottles is the same temperature when the milk is freshly pumped.

Can you put breast milk straight into the freezer?

It is best to allow freshly pumped milk to cool in the refrigerator before putting it into the freezer. This allows the milk to freeze in the correct amount of time. To save time, pour the milk into a freezer bag and label after pumping, then move it to the freezer after it has cooled.

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