Plant-based milk can match or supersede dairy milk in many aspects. Some types provide a similar protein content as cow’s milk with fewer calories and less fat, and plant milk is often naturally rich in vitamins or fortified with them. However, when it comes to cooking, plant-based milk can be challenging due to the possibility of coagulation.
Vegan milk can curdle when combined with acidic or hot substances. This makes adding plant-based milk to the coffee a particularly difficult task. Curdling can also occasionally be a sign that plant-based milk has expired.
Although plant-based milks can curdle, there are several strategies to work around this issue and even some alternative products you can use.
Why Does Plant-Based Milk Curdle
Non-dairy milk is a colloid, meaning the plant base substance (ex. almonds, soy, oats, etc.) is fully emulsified in the liquid (water) substance.
Normally, this mixture is uniform and its components can’t be separated, but contact with heat and/or acidity can cause a reaction that breaks the emulsion and causes coagulation, or “curdling”, of the proteins in plant milk.
This means combining plant-based milk with ingredients like tomatoes, lemons, or coffee can cause curdling, especially when heat is added in cooking or baking.
Curdling is both a physical and chemical problem, but mainly the balance between acid and protein is what determines if plant-based milk will curdle or not.
Non-dairy milk will clump when acidity overpowers the proteins. This can happen when an acid is added to the plant milk or when heat degrades the proteins in the plant milk (allowing acidity to take over).
Can You Drink Curdled Plant-Based Milk
Have you ever brewed a cup of tea that smells like heaven and when you add the milk, suddenly heaven is covered with clouds. Your cup of tea is mixed with curdling milk.
Curdled doesn’t automatically mean spoiled. While it may have an unpleasant texture, curdled plant milk is safe to drink. The separation that occurs due to acidic or high-temperature conditions coming in contact with non-dairy milk does not make the drink harmful in any way.
Additionally, sometimes curdled plant milk is beneficial, like in the process of making tofu where soy milk coagulation helps create solid texture.
If, however, the plant-based milk is curdled in the milk carton, it’s probably spoiled and you shouldn’t drink it.
Look for other signs of spoilage as well: an unpleasant or sour smell, the presence of mold, an expanded container, or thickening. Some milks may have “sediment” collect in the carton, but this is usually vitamin deposits in fortified plant milk and this is why some plant milk requires shaking.
Always check expiration dates and refrigerate plant milk once opened.
Why Does Vegan Milk Curdle in Coffee
Because coffee is both acidic and hot, it’s the perfect storm of conditions to curdle vegan milk.
Plant milk has a “curdle point” acidity of around 5.5 pH. As a point of reference, pure water has a pH of 7 and orange juice is around 3 pH. Black coffee usually has a pH below 5 which breaks the “curdle point”, and the heat of brewed coffee then accelerates the curdling process.
Black tea can also sometimes reach below the 5.5 pH curdle point, but green and herbal teas are well above it with acidities in the 7-10 pH region. Therefore if you don’t mind switching to tea, it might be an easy strategy to avoid plant milk clumps in your morning beverage.
Although coffee curdles many plant milks, not all kinds are affected. Most oat milks don’t seem to curdle in coffee, and other plant-based milks can sometimes be prepared differently to avoid curdling.
If you’re a hardcore coffee fan, there’s still hope to use non-dairy milk with the following strategies.
How to Avoid Plant-Based Milk Curdling in Coffee
To avoid curdling plant-based milk you can use less acidic coffee, use plant-based creamers or barista specialized plant milks, or reduce the temperature difference between the milk and coffee.
Changing the Coffee
The main goal in changing the coffee you’re using is to make it less acidic.
Medium and dark roast coffees are less acidic than light roast. Beans grown in Central or South America are also ideal and avoid African coffees which tend to be more acidic.
Cold brew coffee has the benefit of being less acidic and avoids heat-caused curdling.
If you prefer your coffee hot though, try to dilute it as much as possible (without sacrificing your taste preference) and avoid concentrating the coffee in any form (such as making espresso) which will increase the coffee’s acidity.
Changing the Milk
Another strategy to prevent plant milk curdling is to switch the kind you use.
As stated before, oat milk is an ideal option because it curdles less than other varieties (such as soy or almond).
Rice milk should be avoided as it was found to curdle even in tea. Calcium levels can also play a role in preventing curdling, so it’s advantageous to buy vegan milks fortified with calcium.
Recently, there are also specialized plant-based creamers that are pH-corrected, more stable when heated, and thicker.
These creamers, as well as barista blend plant milks used in coffee shops, are made to blend well with hot coffee and often have extra ingredients to prevent curdling.
For example, the Silk brand creamer has added high oleic sunflower oil, pea protein, potassium citrate, and baking soda not present in the original plant milk. The creamer is about $2.00 more expensive per quart than original Silk almond milk, but since it will be used in smaller amounts (specifically as creamer) than plant milk (used in cereal, recipes, etc.) it should last longer.
Here we have an article about different plant-based milks with their pros and cons.
Changing the Technique
Both whisking and adding the hotter liquid to the cooler one can reduce plant milk curdling by preventing abrupt temperature change. Try starting with plant milk in the mug, then slowly adding coffee so that the milk can slowly warm to match the temperature of the coffee.
Whisking during this process or when adding non-dairy milk to hot coffee will also work to combine the two without curdling.
You can also try adjusting the temperature of either the milk or coffee. Letting the coffee cool before adding plant milk can reduce the acceleration of curdling caused by heat. Similarly, you can try heating the plant milk before combining it with coffee to help incorporate the two more easily.
Be careful not to heat plant milk too aggressively as it can change the texture or flavour.
Heat Tolerance of Different Plant Milks
Due to varying water, fat, and protein contents, each non-dairy milk has a different heat tolerance.
Homemade plant milks usually don’t take as well to heating as commercially produced plant milks and sediment more easily because they aren’t mixed as completely.
Proteins in milk denature if heated too much which can cause curdling, so it’s important to avoid boiling plant milks.
Always try to heat plant milks on low-to-medium temperature settings, and use the following table to avoid overheating and curdling non-dairy milks when cooking or combining with coffee.
| Plant Milk | Max Temp |
| Almond Milk and Oat Milk | 65°C (149°F) |
| Soy Milk and Coconut Milk | 60°C (140°F) |
| Homemade Plant Milks | Avoid Heating |
Stovetop vs Microwave Heating
Both stovetop and microwave heating will increase plant milk’s temperature to reduce curdling in coffee.
When using the stove, make sure to stir non-dairy milk so that a layer of fat won’t form at the surface of the milk as some of the liquid components evaporates.
Stirring also works to prevent burning the milk at the bottom which can ruin the texture and taste.
Layers around the plant milk won’t form in the microwave since the molecules are heated from vibrating caused by radiation rather than via the heat of the pan.
However, to avoid boiling plant milk in the microwave it’s important to only heat in 30-second segments.