Curdled Buttercream

Q: My buttercream curdled after I added some milk to soften it. Why did this happen?

A: Buttercream can sometimes curdle or ‘split’ when milk is added to soften it, and this is particularly common in winter.

Butter is an emulsion of butterfat and water. When you add milk, you are adding extra water to the buttercream (full-cream milk is almost 90% water). If the butter is too cold, it can struggle to incorporate this additional moisture, causing the buttercream to temporarily split or look curdled.

The good news is that it is usually easy to fix. Continue beating the buttercream and, in most cases, it will gradually come back together. The friction created by beating warms the butter slightly, making it softer and allowing it to incorporate the additional moisture and reform a smooth emulsion.

If the weather is particularly cold and the buttercream isn't coming back together, place the bowl in a sink of warm water for 1–2 minutes, stirring frequently, until the buttercream softens slightly. Take care not to let the butter melt. Return to the mixer and continue beating until the buttercream is smooth and cohesive again.

This problem is more likely to occur in winter because ‘room temperature’ butter is generally colder than it is in summer. The bowl, beaters and surrounding air may also be cooler, all of which can lower the temperature of the buttercream and make it more difficult for the butter to absorb the additional moisture from the milk.

Temperature is key when making a buttercream - it needs to be soft enough to incorporate the milk, but not so warm that the butter begins to melt.