How long can I keep my milk...really?




Try two different searches on Google: “milk storage guidelines” and “How long can I save my milk?”

“Milk storage guidelines” gave me 590,000 answers topped by La Leche League and including Ameda, the Centers for Disease Control and Kellymom.

“How long can I save my milk” netted a whopping 67 million hits, the top one from a children’s hospital system parenting site. Baby Center, Medela and Askville were on the first page, as was Dr. Sears’ site.

This may be more a study on Google’s search characteristics than on milk storage, but it reflects the vast variety of information sources out there. My observation is the “milk storage guidelines” search yielded sources with a more “professional” credential, while the more conversational question “How long can I save my milk” added more “informal” sources, including a higher rating for non-professional, mom-to-mom types of advice.

The fact is there are no absolutes. There is a lot of ground between fresh milk taken directly from the breast in sterile surroundings to milk that is spoiled to the point of making a baby sick. And standards have to be higher in various circumstances: certainly there is less room for flexibility in an intensive care unit with tiny, sick babies than for year-old healthy babies.

Evidence based guidelines are important and are constantly updated. But I think moms need to know what factors are involved so they can make informed decisions themselves. What would make milk less safe? What would make milk safe longer?

Keep in mind, the antibodies in milk that help your baby stay healthy also reduce the growth of bacteria in milk in the first place. Bacteria counts in pumped breastmilk actually go down before they start growing. This is why breastmilk doesn’t spoil as quickly as formula and why we can use breastmilk which has been at room temperature even for several hours. On the other hand, freezing destroys some antibodies; so thawed milk needs to be treated more like formula and used within 24 hours.

Here’s the bottom line. There is bacteria in milk from the time it is collected: from mom’s skin, on pump parts, in the air. Bacteria grow in milk. When enough bacteria grows in milk, it is no longer good for baby.

These are the things that affect how much bacteria there is as milk is collected:

  • clean hands
  • clean pump parts, bottles and storage bags
  • clean environment to pump (who wants to pump in the bathroom?)

Once milk is collected, temperature affects how fast bacteria grows.

  • bacteria grows more slowly at cooler temperatures 
  • temperature variations increase bacterial growth

There is less temperature variation in the back of your refrigerator as compared to storage on the door (every time the door is opened, room air is introduced into the refrigerator).

If combining milk, add cool milk to cool milk.

Frost free freezers cycle through a (slight) warming phase to keep frost from building up inside the freezer. It doesn’t really thaw stuff in the freezer, but milk stored in a frost free freezer doesn’t last quite as long.

Usually a freezer attached to your refrigerator will be opened more often than a dedicated deep freeze, so milk in the deep freeze will have a longer life.

Lower freezer temperature increases the length of time milk can be stored.

Breastfeeding & caffeine

You may have seen or heard recent news clips suggesting breastfeeding moms limit their caffeine intake. It is true caffeine is passed into mothers' milk; babies' less mature metabolism doesn't clear the caffeine as quickly as an adult might, creating the potential for caffeine to have a concentrated effect on the baby. 
The reports were not based on new research, but picked up an interview with Dr. Ruth Lawrence published in the February Journal of Caffeine Research. In the discussion, Dr. Lawrence, the author of Breastfeeding: A Guide for the Medical Profession and a well-known breastfeeding authority, pointed out there is no research showing exactly what is a safe level of caffeine for a mother who is breastfeeding. Caffeine in moderation is standard advice for moms. 
Journal of Caffeine Research. December 2011, 1(4): 192-194. doi:10.1089/jcr.2011.1212