Why Alternative Milk Curdles In Coffee And How To Prevent It

It's becoming more common for consumers to turn to dairy alternatives for their morning cup of joe. Whether due to allergies, health goals, or personal preferences, alternative milk options are making a splash in the market. Brands like Chobani's Oat Milk and Blue Diamond's Almond Breeze are gaining ground in the alternative milk industry, while even retailers like Trader Joe's have gotten in the game. No matter your milk, all coffee drinkers can agree that curdled milk is a surefire way to ruin a morning. Alternative milk seems to curdle in coffee more often than regular milk due to differences in temperature and pH, but there are simple fixes to help prevent this!

To understand how to prevent curdled milk, it's important to understand why it curdles in the first place. Coffee is naturally acidic, with a pH of about 4.85 to 5.10, which is partially where the drink gets its signature flavor. The shock when mixing acidic coffee with basic or alkaline level milk is a major contributor to the chemical reaction that causes curdling with alternatives like soy or oat milk, which have varying pH levels. 

Another reason for curdled milk is temperature. When the hot, acidic pH of coffee meets the cold, basic, or alkaline pH of alternative milk, the temperature difference speeds up the chemical process called protein denaturation and leads to curdled milk. Depending on the kind of alternative milk you prefer, there are easy adjustments you can make to enjoy your coffee curdle-free.

A quick solution to prevent alternative milk from curdling is to use a less acidic kind of coffee. Instead of an African coffee, which tends to be more acidic, try a South American coffee, which leans on the less acidic side. Or, to further reduce acidity, try diluting the coffee with a bit of water, such as in iced coffee. To help with temperature-based curdling, try allowing the coffee to cool slightly before pouring in your alternative milk. This will help avoid that protein denaturation process that leads to nasty curdling. You can also try gently warming the milk in small intervals to get it closer in temperature to your coffee before combining the two. Slowly pouring your coffee into the milk – instead of pouring milk into your coffee — is another method to help prevent curdling.

Some alternative milks are more prone to curdling than others. Soy milk is less likely to curdle in hot coffee due to the high protein count, whereas almond milk is more likely to curdle due to a lower protein count. Oat milk holds up pretty well thanks to higher levels of carbohydrates, which help stabilize the protein reaction between the coffee and milk. Coconut milk similarly withstands the curdling process fairly well, thanks to its higher fat content. At the end of the day, if all else fails and you're still getting curdled milk in your coffee with every pour, you can always turn to green tea (check out our recommendations for beginners) or try squeezing lemon juice in your coffee instead.