Why is my breast milk sour in the fridge?

Your breast milk can sometimes taste sour after being stored in the fridge, particularly after being frozen and thawed. This is a common experience.

Reasons for Sour-Tasting Breast Milk

While breast milk is naturally sweet, it can develop a sour or soapy taste for several reasons. Here’s a breakdown:

Lipase Activity: Breast milk contains an enzyme called lipase. This enzyme is essential as it helps babies digest fats. However, lipase can break down fats in stored breast milk, which can result in a sour, soapy, or even rancid smell and taste. This is especially noticeable after refrigeration or freezing.
Diet: Certain foods that you eat can flavor your breast milk. While this is usually subtle, strong flavors may alter the taste and sometimes be perceived as sour. This tends to be less common than the lipase-related taste change.
Storage Method: Improper storage can also contribute to changes in the taste of breast milk. This is usually related to contamination by bacteria or incomplete lipase deactivation.

Here are some practical insights to manage and potentially prevent breast milk from becoming sour:

Scalding Method: To help prevent the sour taste caused by lipase, you can scald your breast milk immediately after pumping before storing. This inactivates the lipase enzyme. The following method can be followed:
1. Heat the milk in a saucepan until small bubbles form around the edges (but do not boil).
2. Remove the milk from the heat and let it cool before transferring it to a storage container.
3. Store in the refrigerator or freezer, as usual.
Proper Storage: Ensure your storage containers are clean and properly sealed to prevent bacterial contamination.
Fresh is Best: Whenever possible, prioritize feeding your baby fresh milk. Frozen or refrigerated milk is best used within the recommended time frame.
Check for Rarity: While sour or soapy milk isn't dangerous for your baby, if it is consistently very sour, consult with your doctor to rule out any other reasons.

Reason	Description	Solution
Lipase Enzyme Activity	Lipase breaks down fats, sometimes resulting in a sour taste, particularly in refrigerated or frozen milk.	Scald the milk after pumping before storing.
Diet	Certain foods in your diet can flavour breast milk and may lead to an altered taste, sometimes perceived as sour.	Be mindful of your diet and adjust as needed.
Storage Method	Improper storage and handling can introduce bacteria or affect lipase activity, leading to taste changes.	Store the milk properly in clean, airtight containers.