If you've ever pulled a bag of frozen milk out, given it a sniff, and thought “that doesn't smell like milk anymore” — you've probably met lipase. Here's what's actually going on, and what you can do about it.

What Is Lipase?

Lipase is a natural enzyme found in breast milk that helps your baby digest fat. It's completely normal — and actually a good thing. The issue is that in some mums' milk, lipase activity continues during storage, breaking down fats and producing a soapy, sour or metallic taste and smell over time.

How Do I Know If My Milk Has High Lipase?

The most common sign is a change in smell or taste after your milk has been frozen for a while — often described as soapy, rancid, or like sour metal. Importantly, this is a taste issue, not a safety issue: the nutritional value of the milk remains intact, even if your baby (understandably) turns their nose up at it.

What Can You Do About It?

Some mums scald their milk before freezing to deactivate lipase, though this involves heat which can affect some nutrients and adds an extra step to an already busy pumping routine. Freeze-drying takes a different approach — the process itself deactivates lipase, often improving the taste of milk that's already been affected, without any added heat at the point of expressing.

If your stash has started to develop that telltale taste, freeze-drying could give it a new lease on life. Learn more on our Freeze-Drying Service page, or check our FAQ for more on the lipase question.