How To Prevent Your Eggnog Latte From Curdling

When Christmas time rolls around, no holiday gathering feels complete without a punch bowl filled to the brim with sweet, creamy eggnog. This festive indulgence is made by whisking eggs and sugar until light and airy, then mixing in milk or cream infused with comforting spices -– and sometimes rum or brandy for a little merry kick. Usually served chilled, when mixed with hot coffee or espresso to make an eggnog latte, its once creamy texture can easily become grainy and curdled. To find out why this happens — and how to prevent it — Food Republic consulted Nelson Serrano-Bahri, chef and director of innovation at the American Egg Board.

"Eggnog will curdle when exposed to extreme heat or acidity," Serrano-Bahri told us. "Espresso is both acidic and hot." When an espresso shot is poured over eggs and milk, these properties can cause the proteins in their natural structure to coagulate. When the unraveled proteins tangle back together, a curdled, uneven texture forms. "Heat shock is largely to blame," Serrano-Bahri told us, but acidity "can also accelerate protein coagulation and fat separation."

In order to prevent this, "You need to temper the eggnog," Serrano-Bahri explained. This simple yet effective technique refers to slowly raising the temperature of the eggnog mix before pairing it with the espresso. This will prevent the milk and eggs from scrambling or curdling due to the sudden heat shock — just think of it as acclimatizing your eggnog to the espresso!

Whether you're adding eggs to chicken noodle soup or making a creamy hollandaise sauce, the key to successful tempering is managing your temperature carefully. "Slowly warm up the eggnog on its own at first, either in a steam pitcher or a saucepan, to approximately [120 to 130 degrees Fahrenheit] (just warm to the touch)," Nelson Serrano-Bahri told us. Take care not to boil your mix, as this will immediately cause it to curdle. "Then, add the espresso or hot coffee slowly while whisking or swirling constantly." This will evenly disperse the milk and egg proteins, preventing them from clumping up.

To be on the safe side, before mixing, you should allow your espresso to cool slightly to reduce the risk of heat shock. "If steaming with a steam wand, begin with the espresso in the cup and add steamed nog slowly, with the pitcher agitating to keep [the] emulsion," Serrano-Bahri added. Remember to add the espresso to the eggnog, not the other way around, as pouring it directly into the hot espresso will immediately cause the proteins to react negatively with the heat. 

Certain types and brands of eggnog also hold up better in lattes than others. "Ultra-pasteurized commercial eggnogs (especially 'barista,' 'high-heat,' or 'ultra-filtered') hold up best," Serrano-Bahri told us. "They're thermally stabilized and can contain carrageenan or gellan gum that resists breakdown." You can also switch things up by making a vegan eggnog, replacing eggs and dairy with plant-based milk, which isn't immune to curdling but often contains stabilizers, and aquafaba, an excellent egg substitute.

When an eggnog latte separates, it means the emulsion of fat, proteins, and water has been broken down. "If it's just slightly separated: Whisk or froth it again for a few seconds," Nelson Serrano-Bahri told us. "Shaking can re-emulsify the fats and proteins." 

"A splash of warm milk (oat or whole) can rebond the texture," Serrano-Bahri added. Another way to prevent curdling is to use the freshest milk available; it is naturally less acidic than older milk, which safeguards against the espresso's acidity, causing the egg and milk protein to denature. Or, you can approach the acidity problem from the other side by choosing a less acidic coffee blend. Light roasts and arabica beans tend to be much more acidic than dark roasts or robusta beans. You could also attempt straining your latte to collect any small clumps, or add cornstarch to stabilize the emulsion, which you incorporate by pre-mixing water and cornstarch into a slurry. Not only will this prevent separation, but it will also enhance the mouthfeel that makes an eggnog latte so satisfying.

"If it's fully curdled (stringy clumps, watery liquid underneath): You can't fix the original emulsion," Serrano-Bahri explained. This is an irreversible chemical change to the protein structures in the milk and eggs, but once you've got the hang of tempering, you're eggnog lattes are guaranteed to come out perfectly smooth every time!