Does breast milk curdle?

In this brief guide, we are going to answer the question “does breast milk curdle” with an in-depth analysis of the possible reasons behind breast milk curdling. Moreover, we are going to discuss the nutritional profile of breast milk and what curdling is. 

So without much ado, let’s dive in and figure out more about it.

Does breast milk curdle?

Expressed breast milk separates into layers of protein, fats, and water when it is stored, thus it can curdle. It does not necessarily mean that it has gone bad. Breast milk stays fresh for up to days when stored at a low temperature.

A mother’s milk remains fresh as long as it is inside the breast but once it is expressed, special care has to be taken in handling and storing it as expressed breast milk lasts for about 3-4 hours at room temperature. It lasts for about 5 days when stored properly in the fridge.

You can read about the proper handling and storage of breast milk here.

Why does expressed breast milk curdle?

As the breast milk is not homogenized therefore when it is stored in the fridge it has the ability to separate into different layers based on differences in densities of various constituents of milk. A creamier layer (containing fats and protein) will float on the surface while a clear watery layer will be present at the bottom. All you gotta do is to give the bottle of milk a little swirl or shake it a few times and the two layers will become one again.

But if you are a bit skeptical about the curdled breast milk, it is better to give it a sniff test as spoiled breast milk has a distinct strong odor.

What is the nutritional profile of breast milk?

Breast milk has a different nutritional profile, flavor, and color than regular milk. It is highly nutritious and contains all the macro and micronutrients that are needed for the proper growth and development of a baby. No doubt that the diet of the mother greatly impacts the quality of the breast milk but mostly breast milk has everything that a growing child needs.

Breast milk has two types of protein. 60-80% of it is whey protein while the rest is casein protein. Moreover, breast milk also contains all the essential fatty acids that are required for the proper nourishment of the baby. Now when it comes to the vitamins part of the milk, that is where the diet of the mother has the greatest impact. Therefore a mother should consume a healthy, nutritious, and wholesome diet so that the baby can get essential vitamins via breast milk.

So lactose is the main carbohydrate and accounts for 40% of the carbohydrates present in the breast milk.  Thus breast milk is important for the proper development and well-being of the child.

Other FAQs about Milk which you may be interested in.

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What do you mean by curdling?

Curdling is the formation of large clumps which are formed when the colloids or the emulsions break down.

The most important constituent of the milk when it comes to curdling is protein. The protein in milk is typically suspended in a colloidal arrangement with the little protein particles moving around freely and randomly. 

In normal conditions, these protein particles repulse one another, permitting them to roam about without clumping. But when the pH of the solution changes, nonetheless, they pull in each other and this results in the formation of larger clumps. This is actually what happens when milk coagulates. 

As the pH drops and turns out to be more acidic, the different atoms of casein protein attract each other and become curdles drifting in the pool of clear whey. One thing to keep in mind about the curdling process is that it takes place more quickly at hot temperatures than it does at cold temperatures.

What are the different ways to curdle milk?

The ways to curdle milk involves changing its overall pH or the temperature of the milk.

Curdling milk by the addition of acid

Milk can be curdled fast by adding any acidic substance like lemon juice or vinegar in it which will change its pH and will result in clumping of the protein part of milk.

For this purpose warm the milk in a utensil gradually until you see steam coming out of it. Add the acidic substance like vinegar, orange juice, or lemon juice to it. Stir it so that the acid can be uniformly incorporated into the whole mixture. The more acid you will add, the larger will be the particles of curd you will obtain. For the acid choice, the most used one is lemon juice followed by vinegar and then orange juice owing to its acidity.

Let it sit for 5-7 minutes and afterward strain it and to separate the curd from the rest of the mixture.

Curdling milk by heating

For this process pour the milk into a saucepan and let it boil 1-2 minutes after it reaches the boil. Stir the milk occasionally but do not overdo it as we want the milk protein to clump together. The milk will start curdling once it reaches the temperature of 180 Fahrenheit or more than that. Remove the saucepan from the stove and allow it to sit for 5 to 10 minutes. You can let it stand for even longer if you need more curdling effect. Afterward, strain it.


In this brief guide, we answered the question “does breast milk curdle” with an in-depth analysis of the possible reasons behind breast milk curdling. Moreover, we discussed the nutritional profile of breast milk and what curdling is.