Have you noticed that the amount of milk you express when you pump varies? Sometimes you might express enough for a full feeding, while other times it might only be enough for a partial feeding. No worries—you can combine smaller amounts of milk expressed at different times to make a full feeding. I call this building a bottle.

To build a bottle, pump both breasts. When you are finished, combine the milk you expressed from the right and left breasts into one container. Seal it. Put this milk in the refrigerator. Let’s call the milk from this first pumping session milk 1.

Repeat the process next time you pump. Combine the milk expressed from the right and left breasts into one container, seal it, and cool it. Let’s call the milk from this pumping session milk 2.

Once cooled, you can pour milk 2 into the container of milk 1. If this is enough for a full feeding, great! Otherwise, continue to pump, cool, and combine milk until you build a bottle with the right amount of milk for your baby.

If you are pumping your milk strictly to build a freezer stash, go ahead and put milk 1 directly into the freezer. After pumping again, cool milk 2 and then you can pour it onto the frozen bottle of milk 1, and so on.

When building a bottle of milk in the freezer, you will notice obvious layers. This is normal. When you defrost your milk, simply give it a gentle shake to mix the milks that were pumped at different times. Your baby will never notice the difference.