Why does soy milk curdle?

In this brief guide, we are going to answer the question “why does soy milk curdle” with an in-depth analysis of why soy milk curdles. Moreover, we are going to discuss whether or not soy milk curdles in coffee and tea. 

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

Why does soy milk curdle?

There are two factors, temperature, and acidity, that are chiefly responsible for the curdling of soy milk. Now when it comes to curdling soy milk, we can do it on purpose by the addition of some acidic item in the hot soy milk or this process can also take naturally when soy milk is added to a strong cup of coffee. 

The curdling behavior of soy milk was not observed when it was added to tea. We are going to discuss these points in detail so that you better understand the curdling of soy milk.

Curdling soy milk

Curdling is the formation of large clumps which are formed when the colloids or the emulsions break down. So what you gotta do to curdle soy milk is to add it into a saucepan and heat it until the steam begins to come out of it. 

Add any acidic substance to it. For one cup of soy milk, you have to add one tbsp of lemon juice. Stir it thoroughly. 

Then remove the saucepan from the stove and let it sit for 10 minutes. Afterward, strain it to separate the curd from the rest of the mixture. Soy milk is curdled on purpose for the preparation of tofu. 

You can read more about tofu here.

To understand why soy milk is curdled, you have to understand the composition of soy milk and its main constituents owing to which it is curdled.

One cup of soy milk has 80-100 calories in it. It is a good source of protein and has about 7 grams of protein, 4 grams of fat, and 4 grams of carbohydrates. 

It is a good source of potassium and comes fortified with calcium, vitamin D, and vitamin B12. It has a very low amount of saturated fat present in it and does not contain cholesterol that makes it an odd low-calorie milk substitute.

Now when it comes to curdling, it is the protein part of soy milk that plays the main role. The protein in soy 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 drops and becomes more acidic, they pull in each other and this results in the formation of larger clumps. 

This is actually what happens when soy milk coagulates. 

Other FAQs about Milk which you may be interested in.

Can coconut milk be substituted for milk?

Can you substitute almond milk for milk in pancakes?

How long does coconut milk last?

Soy milk curdling in coffee

Acidity is the main reason behind soy milk curdling. As we all know that ground coffee, instant coffee, or black coffee is more acidic than soy milk itself. Being more acidic means that the pH of the coffee is lower as compared to that of the soy milk. 

Soy milk has a curdle point of 5.5 while the pH of the coffee is 5. So when high acidic coffee comes in contact with the basic soy milk, it makes the soy milk curdle. 

It coagulates the soy milk and the clumps soy milk settles on the base of your cup, leaving you with a cup of coffee that is just a disappointment.

Heat accelerates the process of curdling soy milk. The hotter the temperature is the more are chances for soy milk to curdle. 

So when it comes to coffee, heat combined with the high acidity of the coffee serves as the icing on the cake and curdles your soy milk.

It is worth mentioning that as long as the coffee beans and the soy milk that you used to make the espresso were fresh, you can drink the curdled soy milk coffee in light of the fact that the reason behind soy milk curdling in this situation was the high acidity of the coffee that eventually changed its pH and brought about soy milk clumping and curdling. 

One thing to remember is that it won’t have that incredible taste or mouth feel to it however it likewise won’t cause health problems even if you gulp it down.

Soy milk curdling in tea

Soy milk does not curdle in tea, therefore if you want to go for a cup of your favorite tea with soy milk, you can go for it without worrying about the curdling.


In this brief guide, we answered the question “why does soy milk curdle” with an in-depth analysis of why soy milk curdles. Moreover, we discussed whether or not soy milk curdles in coffee and tea.