High lipase in breast milk can affect the taste and smell of expressed milk. Lipase is a natural enzyme found in breast milk that helps break down fats, making them more digestible for infants. When lipase levels are higher than average, the fat breakdown process can accelerate, which may lead to changes in the milk’s flavor and odor. Often, breast milk with high lipase develops a “soapy” or “metallic” taste after being stored, even when properly refrigerated or frozen. While this change does not make the milk unsafe, some babies might refuse it due to the taste.

It’s important to distinguish high lipase from the oxidation of breast milk. Oxidized breast milk tastes rancid or sour/spoiled even when stored per usual guidelines. It’s caused by drinking water that may contain copper or iron ions, and from taking  fish-oil and flaxseed supplements or eating a diet high in polyunsaturated fats.

If you’re dealing with high lipase in breast milk and want to reduce the taste changes, here are a few strategies that may help:

Scald the Milk: heating it to around 180°F (82°C) until you see small bubbles around the edges but not a full boil—can inactivate the lipase enzyme, stopping further fat breakdown. This process needs to be done immediately after pumping, before storing the milk in the fridge or freezer

Trial of Different Storage Techniques: Although high lipase is an inherent trait in the milk, storage methods can sometimes influence how quickly the milk’s taste changes. For example, freezing milk immediately after pumping may slow down the enzymatic activity more effectively than refrigeration

Offer Freshly Pumped Milk: For families who don’t need to build a large freezer stash, offering freshly pumped milk can avoid the taste change issue altogether. Since high lipase typically impacts milk stored for longer periods, using milk within a few hours after pumping can maintain the taste and avoid baby’s rejection

Experiment with Mixing Fresh and Stored Milk: If scalding or using only fresh milk is impractical, some parents have success blending fresh milk with previously frozen milk, which can dilute the taste changes enough to be acceptable to their baby