Why Does Oat Milk Separate In Coffee?

January 28, 2024 | Coffee 101

Written By: Millie Pham
Last Updated: January 28, 2024

Why Does Oat Milk Separate In Coffee? Quick Answer

  • Your oat milk separates in coffee probably because the coffee's acidity clashes with the lactic acid in the oat milk. 
  • It might also separate if the oat milk hits the hot coffee straight from the fridge, shocking it into curdling. 
  • Additionally, your oat milk could separate in coffee if it lacks enough emulsifiers to keep it stable.

We've all experienced it: you pour yourself a comforting cup of coffee, mix in some oat milk, but as you take a sip, you notice it's not quite right.

The milk has separated, leaving your coffee looking less than appetizing. It's a frustrating start to the day, to say the least.

While oat milk is a popular dairy alternative for its creamy texture and eco-friendly footprint, it doesn't always behave as expected in coffee.

After trying out numerous cups and diving into the science of it, I've figured out a few main reasons why oat milk often separates in coffee, rather than mixing into the smooth, perfect blend we're all after.

Here are six reasons why your oat milk separates in coffee:

1. Acidity of Coffee

When it comes to coffee, acidity is a key player. This isn't about how sour or bitter your coffee tastes, but rather about the natural acids found in coffee beans.

In simple terms, these acids are what give your coffee a bit of zing and a fresh, lively flavor.

Now, here's where it gets interesting with oat milk.

Oat milk, like many other milks, has something called lactic acid. It's totally normal and not something to worry about.

But when you pour oat milk into your coffee, this lactic acid meets the acids in your coffee, especially acetic acid. If your coffee is really high in these acids, it can throw off the balance and cause the oat milk to react in a way we call 'curdling.'

It's when the oat milk doesn't mix smoothly and might look a bit chunky or separated. This doesn't mean your coffee is bad. It's just a bit of a mismatch in the dance of ingredients.


So, if you're seeing this happen, you might want to try a coffee with less acidity. This could be a darker roast or a coffee labeled as low-acid. 

These coffee types have less zingy acid, so they're more likely to get along with oat milk and keep your coffee looking smooth and delicious.

2. Temperature Difference

Here's something simple about mixing oat milk in coffee: temperature matters a lot. Imagine taking a warm shower and suddenly getting a burst of cold water. That's a shock, right?

The same thing can happen to oat milk when it's cold from the fridge, and you pour it into hot coffee.

This sudden change from cold to hot is like a shock for the oat milk. What happens next is the oat milk can get all flustered and start to curdle.

Curdling is when the milk doesn't mix well, and you see little clumps or layers instead of a smooth blend.


To avoid this, you can try warming up your oat milk a bit before adding it to your coffee. You don't need it hot, just room temperature or slightly warm.

This way, the oat milk and coffee are more like friends meeting in a comfortable room, rather than opposites in a surprise encounter.

By doing this, you're giving your coffee and oat milk a better chance to mix well, making your drink smooth and enjoyable

3. Lack of Emulsifiers

Let's break down the role of emulsifiers in oat milk, keeping it straightforward.

Emulsifiers are like the glue that holds the different parts of oat milk together. Oat milk is made of water, oats, and sometimes added oils [1].

Water and oil don't mix well on their own – they're like two people who aren't really friends. Emulsifiers are the mutual friend who helps them get along.

When oat milk doesn't have enough of these mutual friends, or if they're not very good at their job, it can start to separate, especially when mixed into coffee.

This is similar to how oil separates from vinegar in a salad dressing if you leave it sitting for a while.

The separation, or curdling, happens because the oat milk can't hold itself together in the new environment of the coffee, which might be hot or acidic.


To avoid this, switching to a milk brand that's made for coffee use. 

Some oat milks, particularly those labeled for baristas or coffee, are specifically designed with the right amount and type of emulsifiers. 

These emulsifiers are better at keeping everything mixed together, so when you pour the oat milk into your coffee, it stays smooth and doesn't separate.

4. Quality of Oat Milk

The quality of oat milk can really affect how it behaves in your coffee.

Not all oat milks are created equal – some are like high-performance athletes, while others are more like casual joggers.

Higher quality oat milks are often designed to handle the tough environment of a steaming cup of coffee.

They come prepared, with the right balance of ingredients and stability to face the heat and acidity.

On the other hand, lower-quality oat milks might not be up for the challenge. They can get overwhelmed when they hit the hot, acidic coffee and start curling or separating.

The difference often comes down to how the oat milk is made.

The better ones might have more effective emulsifiers (just like I said earlier), a more balanced fat content, or be processed in a way that makes them more stable.

Some are even labeled as 'barista' or 'coffee' blends, meaning they're specifically made to work well with coffee.


So, when picking your oat milk for coffee, it might be worth investing in a higher-quality brand, especially if you love a good coffee. 

It can make the difference between a smooth, creamy cup and a lumpy, separated one. Remember, with oat milk, sometimes you really do get what you pay for

5. Fat Content

The fat content in oat milk can be a big deal when it comes to mixing it with coffee. It's all about balance.

Oat milk with more fat tends to be like a strong swimmer in the ocean of coffee – it holds its own and mixes in smoothly.

This is because fat can help stabilize the milk, making it less likely to curdle when it meets the hot, acidic coffee.

But, if your oat milk is on the lower fat side, it can struggle to stay mixed in with the coffee and might end up separating or curdling.

The lower fat content means there's less to help the oat milk maintain its composure against the coffee's heat and acidity.


So, if you're finding that your oat milk doesn't play well with your coffee, you might want to check the fat content.

Choosing an oat milk with a bit more fat, which can hold up better.

6. Storage Conditions

How you store your oat milk can really make a difference, especially when you add it to your coffee. If your oat milk is stored right, it's more likely to mix well into your coffee without any issues.

Keeping oat milk in the fridge at the right temperature is key. If it's left out too long or not stored at the right temperature, it can go bad faster.

Also, once you open a carton of oat milk, it's important to use it within a reasonable time. Generally, opened oat milk should be used within 7 to 10 days for optimal freshness and quality.

So, if your oat milk has been sitting open in the fridge for a while, it might not be at its best for your coffee.

In short, keep your oat milk stored properly in the fridge, and try to use it while it's still fresh. This way, you're more likely to enjoy a smooth, curdle-free coffee experience

Millie Pham

Hi there! I'm Millie Pham, a devoted brewer and tea lover at heart. As the founder of Bean Leaf Cup, my mission is to share my tea and coffee expertise with you all. I firmly believe that creating a fantastic cup of tea or coffee should be easy for everyone. No matter if you're already a coffee or tea expert or just beginning your journey, I'm here to help you navigate the world of brewing. Welcome aboard!

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