Aug 14

My Baby Refuses To Drink My Stored Milk

Why do some women find that their stored (cold or frozen) milk develops an unpleasant or rancid smell? Some babies won’t drink this milk though others don’t seem to notice.

Why Does This Happen?

Mothers’ milk is amazing…. It contains special enzymes to help baby digest fat. When milk is stored these enzymes start to break down fat (triglycerides) even when milk is cold or frozen.

Most of the time this fat breakdown causes no problems, but the release of chains of fat called Free Fatty Acids (FFA) can cause milk to smell or taste bad.

It does not make the milk bad!

We know from a recent study that this milk is fine for babies to drink (if they don’t mind the taste). It has normal amounts of nutrients, no excess bad bacteria, and causes no tummy troubles for babies.

It is not sour, it is not spoiled, it is safe for baby to drink.

Milk banks actually use this donated milk that babies reject to feed little preemies and they do just fine. We think that all stored milk develops these FFAs and it may be that some moms have a stronger enzyme and some babies are just pickier about taste.

How Long Does It Take To Happen?

It is super variable in how long this takes to happen. Some mothers finds their milk turns overnight in the fridge, and for others it takes months even in a deep freezer to happen. In general colder temperatures and shorter times in storage decrease the chance of the milk developing an unpleasant smell.

What Can I Do To Prevent This?

If baby rejects the milk and it has a rancid smell; mother can try a little scientific treatment of her milk to disable that milk enzyme that is called Lipase. She can heat her pumped milk either in the microwave or on the stove in a water bath – it doesn’t even have to boil to hit between 115-160 degrees F (boiling is 212 degrees F)- and then cool it down and store it.


With trial and error (and maybe a kitchen thermometer) as to how and how long to heat the milk, most moms can do this mini pasteurization step before milk is put in cold storage and avoid throwing milk away. Do this heating step in an appropriate container- not plastic. Although it is true that the heating will kill most cells and bacteria and some of the biologic factors in milk, if baby is also breastfeeding each day it should be fine, and is certainly better than infant formula!

What Can I Do If I  Have Excess Milk My Baby Won’t Drink?

Milk that your baby doesn’t drink due to the poor taste is not bad for baby’s tummy, and they may like it mixed in with baby food. It is also fine to donate for feeding NICU babies so if you have over 100 ounces of milk your baby rejects please consider donating it to a non-profit milk bank like San Diego Mothers’ Milk Bank.

Lisa Stellwagen MD, FAAP  Professor of Clinical Pediatrics at UC San Diego Health