Oat milk can sometimes curdle or separate when added to coffee. It's important to note that while curdling or separation can be unappetizing in appearance, it typically does not affect the safety or taste of the beverage. There are a few reasons why separation and curdling might occur: 1. Oat milk is more likely to curdle if your coffee is too hot (above 160F) or if you're using highly acidic coffee. Either of these situations can cause the proteins in oat milk to coagulate and separate, resulting in a curdled appearance. Try allowing your coffee to cool slightly before adding oat milk and/or opt for a less acidic coffee blend to minimize the chances of this happening. Alternatively, consider adding a pinch of baking soda to your espresso grounds before brewing to help increase the pH. 2. Different brands of oat milk have wildly different reactions to coffee. Some brands are specifically formulated to withstand higher temperatures and acidity, reducing the likelihood of curdling. If you find that your oat milk consistently separates or curdles in coffee, it may be time you switch brands to a barista-approved variety like Oatly. 3. Oat milk can separate over time, especially if it's been languishing in the door of your fridge for some unknown period of time. Shake the container well before using it to ensure that it is well-mixed. 4. How you add oat milk to your coffee can also affect its tendency to curdle. I recommend that you add the oat milk slowly and gradually while stirring or swirling the coffee to distribute the milk more evenly and reduce the chance of curdling.