Why does my expressed milk smell bad? Is it spoiled?
As you thaw a bottle of expressed breastmilk for your baby, you notice a bad smell, soapy or sour, and your heart breaks to realize the stash of “liquid gold” you've worked so hard for is unappetizing, or worse, unusable.
The first thing to do is make sure you're handling and storing your milk properly (link to storage guidelines) to reduce the risk of bacterial contamination.
A rancid smell may be a sign of chemical oxidation that's caused by certain polyunsaturated fats in your diet or minerals in your drinking water. Switching water sources and avoiding DHA supplements like fish or flaxseed oil may help.
Milk that smells soapy, metallic, or “like vomit” may be a sign of excess lipase.
Lipase is an enzyme that breaks down fats, making your milk easily digestible and releasing vital nutrients and fatty acids.
Some mothers' breastmilk contains too much lipase. Though unnoticeable when your baby nurses at the breast, the excess lipase gradually digests the fats in stored expressed milk, causing the changes in smell. The taste of the milk may or may not be affected, depending on the extent of the problem. If your baby accepts it, there's nothing else you need to do.
Once the fats are broken down, the milk can't be “fixed.” That's the bad news. The good news is that you can prevent it in the first place.
The key is to scald freshly expressed milk before storing it, to deactivate the lipase enzymes while leaving many, if not all, of the nutrients and immune factors intact.
To scald the milk, put it in a glass or BPA-free plastic container and heat the container in water. You can use a pan on the stove, a crock pot, or -- the method that many mothers find easiest -- a bottle warmer. Just make sure it's not the type that turns off automatically when it gets too hot.
Measuring with a digital cooking thermometer, heat the milk to:
144.5F/62.5C for 1 minute or
163F/72C for 15 seconds or
180F/80C and immediately remove from heat
Place the container of scalded milk directly into a bowl of water and ice (glass may crack; use a plastic container for cooling). The ice bath cools the milk quickly and prevents bacteria growth. Once the milk is cool, store it as usual. Try a few test batches before you start to build a stash.
Microwaves aren't recommended for scalding because they heat unevenly and you can't tell when the milk is at the right temperature.
If your baby rejects the milk you stored previously and you have a freezer full of milk you can't use, consider donating it to a milk bank. Milk banks combine milk from many different mothers and pasteurize it, significantly diluting the milk that has excess lipase. Your unusable milk could be a lifesaver for another baby.
(info on milk banks)