Can Oat Milk Curdle?

Written by: Kelly Donovan

As oat milk continues to increase in popularity, many of us find ourselves asking questions about this dairy-free product, such as "Can oat milk curdle?"

In many ways, oat milk behaves quite similarly to regular dairy milk, and this includes the ability to curdle. Oat milk can and does curdle when the temperature or acidity of its environment causes a chemical reaction.

Continue reading to find out why oat milk curdles, plus some helpful tips for prevention so that you can get back to enjoying your morning brew.

Does Oat Milk Curdle?

Yes, oat milk can curdle just like any other type of milk. In many cases, oat milk behaves in a very similar way to standard dairy varieties.

When your oat milk curdles, it can leave you feeling like you're drinking two different drinks, and your morning coffee will not provide the same nourishment as usual.

This happens because of the high levels of heat and acidity in your coffee that cause high-energy chemical reactions.

Why Does Oat Milk Curdle?

Oat milk curdles when the pH value drops into an acidic range. This happens because of chemical reactions in the milk, as detailed below.

The Coffee Bean is Highly Acidic

There are many different coffee beans available for your hot beverages, and the one you choose can either increase or decrease the chance of your oat milk curdling.

The more acid contained in your coffee beans, the higher the chance that your milk will curdle. 

coffee beans spilled over table

You're Adding The Milk Too Soon

Many of us love to add a splash of milk to a freshly brewed beverage, but this could be causing your oat milk to curdle. 

As we know, the higher the temperature, the greater the rate of reaction.

So if you add the milk as soon as you've brewed the coffee, there is a much higher chance that your oat milk will curdle.

Thanks to the rules of thermodynamics, when you allow a cup of coffee to sit, the temperature will reduce naturally.

But if you add milk, the heat does not flow out of the cup in the same way and instead begins to react with the milk.

The Cup You're Using Isn't Clean

If you're using an unclean cup, mug, or bowl for your oat milk, you'll find that the milk is more prone to curdling.

Any coffee still clinging to an unwashed cup will raise the overall acidity level in the cup, making the milk more likely to curdle.

And it's not just utensils with leftover residue that are the problem, but also utensils that you haven't used for a while.

If your cup or bowl contains dust, it will react with the oat milk and cause it to curdle.

Your Oat Milk Has Expired

If your oat milk is spoiled, it will be much easier for it to curdle because it already possesses a higher acidity level.

Many manufactured products contain an acidity regulator to help prevent this from occurring, but there is a good chance that the milk will de-emulsify if spoiled.

Oat milk has a shelf life of around nine months because when it's sealed, there is no chance of exposure to microbes or product deterioration.

But, once you open the product, you'll need to keep it refrigerated and consume it within 7 to 10 days - any longer, and there's a very good chance your milk will spoil.

In addition, your milk could expire much faster if it is homemade.

Many manufactured oat milks contain dipotassium phosphate to act as their emulsifier; this regulates acidity and helps to minimize any rapid pH level changes.

If you make your own oat milk, you'll want to create an emulsifier to get a smooth texture and reduce the chance of curdling.

man holding stomach with glass of milk on table

You're Not Storing Your Oat Milk At The Right Temperature.

Where you store your oat milk matters; if you expose it to room temperature or higher for long periods, there is a good chance it will spoil.

Then, when you pour it into a fresh cup of coffee, it's increasingly likely to curdle.

Instead, manufacturers recommend that you store oat milk below room temperature.

How to Stop Oat Milk From Curdling

It can be really annoying when you prepare to take the first sip of your morning brew, only to discover that the milk has curdled, and you'll have to make a fresh cup.

Here are some tips to help prevent this from happening.

Use A Low Acidity Coffee Bean

The acidity levels of the coffee beans should be easy to spot on the packet when you go shopping.

By selecting a low acid bean, you decrease the overall amount of acid in your beverage and reduce the risk that your milk will curdle.

Add The Milk First

Instead of waiting for your coffee to brew before adding the milk, try this.

Make the oat milk the first thing you add to the cup, then slowly pour the coffee over it.

For the best results, allow the coffee to cool to room temperature before adding it to the milk. This helps the milk slow down its absorption rate, making it less likely to curdle.

woman pouring oat milk into mug

Use Fresh Oat Milk and Keep It Refrigerated

In general, use oat milk within three weeks of purchase to maintain its freshness (you may want to reduce this time if you're drinking homemade milk). 

And ensure that you follow the manufacturer's instructions for the best storage policies.

Remember that they've tested their product against various heat treatments and know the optimum temperature for keeping the product fresh.

In general, once you've opened the milk, you'll need to consume it within 4-7 days, but it can last for up to 10.

If you want to protect the integrity of the product, keep it cool (i.e., store it in the fridge); the longer you leave the milk in an ambient room temperature environment, the faster it will spoil.

Additionally, avoid air exposure where possible as this helps to reduce the risk of the milk spoiling.

Many manufactured products come with this type of packaging, but you'll need to purchase an airtight container for storage if you make your own milk.

Don't Overheat The Milk

Keep your milk below 70 degrees celsius at all times, even when frothing. This helps to reduce the rate of any chemical reactions and makes curdling much less likely.

Look For Products With A High Calcium Content

Many manufactured oat milks have added calcium to enhance the product's taste.

This makes the product more palatable, and it also reduces the levels of acidity, thus making curdling much less likely.


Does Oat Milk Curdle When Heated?

Not all oat milk curdles when heated; it all depends on the type you use, its natural acidity level, and whether you add an espresso shot.

Milk curdling is a chemical reaction. These reactions increase as you elevate the temperature, so it's inadvisable to heat any milk to a high temperature - including the oat variety.

If you are frothing the milk, keep the temperature to a maximum of 70 degrees celsius, which should help prevent overheating and curdling of the milk.

Why is My Oat Milk Separating?

It's pretty standard for oat milk to separate if you leave it idle for a while.

Separation of milk is a different reaction to curdling; it simply means that the water has separated from the other ingredients in the oat milk.

To rectify this, you can give the liquid a shake (helping the ingredients emulsify again).

If you're making your own oat milk try using a natural product such as sunflower lecithin powder to prevent the product from separating.

Why Does Oat Milk Curdle in Coffee?

Oat milk will curdle in your coffee if you subject it to specific acidity levels. Oat milk contains acid, as do coffee beans; when you heat both elements to a high temperature, you increase the reaction rate.

The more heat you add to this compound, the higher the chance that your oat milk will curdle.

Why Does Oat Milk Curdle in Iced Coffee?

You may well be asking, "If heat causes milk to curdle, then why would this reaction still occur in iced coffee?"

Good question - but there are two very good reasons.

Firstly, it's not just the temperature that causes the reaction in oat milk; the temperature merely speeds up this reaction. It is also the acidity levels.

Just because the coffee is cold, there could still be an excess of acid, which causes your milk to curdle.

Secondly, many people heat the milk before adding it to ice coffee.

This is a popular option, thanks to the sweetness of warmed milk.

If you opt to heat the milk for an iced coffee, keep it below 70 degrees celsius, and you shouldn't have too many problems.

Final Thoughts

Like any other milk, oat milk can and will curdle for many reasons.

The most important thing is to ensure that your product is fresh, as drinking anything that has bacterial growth can damage your health.

While curdled milk is less likely to damage your health, the taste isn't exactly inspiring!

If you want to avoid this annoying reaction, opt for low acid coffee beans, clean utensils throughout before use, and always keep the milk temperature below 70 degrees celsius.

About the Author

Kelly Donovan is a freelance writer. She enjoys helping people reach their wellness goals by educating them about how food plays a role in their health.