Why Does Soy Milk Curdle In Coffee? How to Fix It

crazy by Editorial Staff | Posted on March 31st, 2023

If you add soy milk to coffee, you may notice that it curdles and separates from the coffee. This can be an unpleasant surprise for many coffee lovers and may leave them wondering why this happens.

In this blog post, we will explore the science behind why soy milk curdles in coffee and what you can do about it.

Soy Milk

What is soy milk

Soy milk is a non-dairy alternative often used as a coffee creamer. It is made from whole soybeans or soy protein isolate, water, and other additives such as sweeteners, vitamins, and minerals. Soy milk is known for its creamy texture and nutty flavor that can complement the taste of coffee. 

The popularity of soy milk as a coffee creamer

Soy milk has become increasingly popular for those looking for a dairy-free option. The creamy texture and mild flavor of soy milk make it a desirable alternative to dairy, and many baristas have honed their skills to create latte art and smooth foam with soy milk.

What is curdling

Curdling is a process in which a liquid, such as milk, separates into solid curds and liquid whey. When milk curdles, the proteins, specifically casein, coagulate and form solid masses or curds, while the liquid whey separates.

The problem of curdling

Many coffee drinkers with lactose intolerance or a preference for non-dairy milk face the problem of curdling problem when they switch to a soy milk creamer. While some may find the texture of curdled soy milk tolerable, others prefer a smoother and creamier experience. This can be frustrating, especially for those who rely on non-dairy alternatives. 

What causes curdling?


Acidity is one of the main culprits behind the curdling of soy milk in coffee. Soy milk’s proteins react to the acidity of the coffee, causing the milk to curdle. Coffee, with a pH of around 5, is more acidic than soy milk, with a curdling point of around pH 5.5. 

This difference in acidity levels makes soy milk particularly susceptible to curdling when mixed with coffee.


Temperature plays a crucial role in the curdling of soy milk in coffee. When it comes to temperature, if soymilk rises too quickly, it will curdle. Temperature can cause curdling by altering the structure of proteins in a liquid, such as milk. 

When a liquid is heated, the proteins denature, meaning their three-dimensional structure unravels and changes. The proteins may coagulate and form solid masses or curds if the temperature or heating time is too high.

Presence of alcohol

The presence of alcohol can cause curdling in soy milk. This is because alcohol disrupts the natural balance of proteins in the liquid, causing them to denature and clump together. For example, if you add whiskey or another high-proof alcohol to soy milk, the sauce may curdle and form small lumps.

How to prevent curdling

The following ways can prevent curdling:


Emulsifiers are a common ingredient found in many types of milk, including soy milk. These substances are added to milk to prevent curdling by effectively blending the fat, protein, and water molecules. 

Studies show that emulsifiers reduce the surface tension of the milk by creating a thin layer of fat around each protein molecule. This layer helps to keep the proteins suspended and dispersed throughout the milk, preventing them from clumping together and curdling. 

Incorporating emulsifiers into soy milk can help to prevent curdling when added to coffee, even if the coffee is acidic. However, some people prefer to avoid emulsifiers in their food products due to concerns about their potential effects on health. For those individuals, alternative milk options are available that do not contain emulsifiers

Pre-heating soy milk

One solution that works for many is pre-heating the soy milk before adding it to the coffee. Gently heating the milk before introducing it to the coffee can help prevent curdling caused by the proteins in the soy milk reacting with the acidity in the coffee.

Adding coffee slowly

Adding coffee slowly is a great way to prevent curdling when using soy milk as a coffee creamer. As mentioned earlier, abrupt temperature changes can cause curdling, so adding coffee slowly helps to slowly increase the milk’s temperature and decrease the rate of curdling.

Adding a pinch of salt

Adding a pinch of salt can be a possible solution to prevent soy milk from curdling in coffee. As discussed earlier, curdling happens when the acidic nature of coffee reacts with the protein content in soy milk. 

Salt can counteract this reaction. Adding just a pinch of salt to your coffee makes soy milk less likely to curdle. This little hack can be quite helpful for those who regularly enjoy soy milk in their coffee. 

Remember, adding too much salt can alter the taste of the coffee, so it’s best to use it sparingly.

Other alternatives to soy milk

For those who can’t tolerate soy or are looking for alternatives to prevent curdling in their morning coffee, there are a few options to consider. 

Almond milk

Almond milk is a popular alternative to soy milk for those who experience curdling in their coffee. Almond milk can also curdle when mixed with coffee due to the drink’s high acidity and temperature. 

Besides, studies show that being a great coffee creamer, almond milk is high in vitamin E, making it a healthy choice. Like soy milk, it is an excellent dairy-free option for vegan or lactose intolerant. 

Additionally, it has a slightly nutty taste that pairs well with coffee’s bold flavor, making it a popular choice amongst coffee drinkers.

Oat milk

Oat milk is becoming an increasingly popular alternative to dairy and soy milk in coffee shops and households. Its mellow, smooth, and slightly sweet taste makes it an excellent choice for coffee lovers who want a rich and creamy texture without the added sweetness of dairy. 

While soy milk tends to curdle when heated, oat milk has a high tolerance for temperature changes, making it less likely to curdle in your coffee. However, for the best results, it is recommended to preheat the oat milk before adding it to your coffee and to add the coffee slowly to prevent any separation.

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Disclosure: No compensation or free products were received in exchange for writing this review.


Editorial Staff

The editorial staff at Crazy Coffee Crave is a team of coffee enthusiasts & Baristas who enjoy the one thing we all think about as soon as we get up in the morning. Trusted by thousands of readers worldwide.