Runny buttercream is almost always down to one thing: too much liquid in your mix. It’s usually simple to fix – add sieved icing sugar a spoonful at a time, and mix each spoonful in well. Eventually it will be firm enough to pipe and decorate with.
This guide covers classic American buttercream (butter and icing sugar) – if you’re working with a meringue-based buttercream, the causes are a little different.
Why Buttercream Goes Runny
Runny buttercream is just a balance problem. Too much liquid = too runny. The ratio of fat and sugar to liquid has tipped too far toward liquid, so the mixture can’t hold its shape. Common causes:
- Too much liquid. Perhaps you’ve been a bit heavy handed with the milk, cream or flavourings? Especially if you’ve added them all at once rather than gradually
- Butter that was too warm. If it was left out too long or started to melt slightly during mixing, your whole mixture loses structure
- A warm kitchen or warm hands. Buttercream is super temperature-sensitive – a hot day or a lot of handling can soften it past the point of holding shape
- Not enough icing sugar. If you’ve used more butter than icing sugar, then things can start to get soupy. Sometimes it’s just a ratio issue from the start, particularly if you’re scaling a recipe up or down
The Fix, Step by Step
- Add icing sugar gradually. Sieve in a spoonful at a time, mixing on low-medium speed between each spoonful. Stop as soon as you get back to a stable, pipeable consistency. Go gradually, as it’s easy to overcorrect and end up with buttercream that’s too stiff instead!
- If it’s too warm, then chill it first. Pop the bowl in the fridge for 10-15 minutes, then re-mix it on medium speed. This can bring a warm, runny buttercream back without needing to add extra sugar (which can make it overly sweet).
- If it’s a regular problem, check your butter-to-sugar ratio. If your buttercream regularly resembles soup, it might be worth tinkering with your recipe rather than fixing it each time. I like a 1:1 ratio of butter to icing sugar.
How to Stop it Happening Again
- This one might be controversial, but just don’t add liquid! I’ve never had to use milk or cream to loosen up stiff buttercream. Keep it simple with just butter and icing sugar and you reduce the risk of having runny buttercream
- If you do add any liquid, do it slowly, in small increments and mix as you go. It’s easy to overdo it!
- Keep your butter properly cool but softened – not warm or melting
- Work in a cool room (where possible), especially in summer. Even just closing the curtains and working away from direct sunlight can make a big difference.
- And if your kitchen’s like the fiery depths of hell in summer, then try chilling your bowl before you start. You can also pop your mix in the fridge intermittently, just to stop it getting too warm while you’re mixing.
Dealing with the other problem of buttercream that’s split rather than runny? Head over to Why Did My Buttercream Split? for the solution
Frequently Asked Questions
Can I fix runny buttercream without adding more sugar?
Yes – if it’s a temperature issue rather than a ratio issue. Pop your bowl of runny buttercream in the fridge for 10 minutes and give it another whip. This should firm it up without needing to add extra icing sugar
Will adding more icing sugar make it too sweet?
A small amount of extra icing won’t noticeably change the sweetness, but it’s worth adding gradually rather than all at once so you don’t overdo it
Why does this happen more in summer?
Warmer temperatures mean softer butter. As it’s 50% of your buttercream, the softer the butter, the softer the whole mix. Extra icing sugar and a little more chilling in summer will help avoid your buttercream getting runny