How to Thicken Frosting for Cakes and Cookies
When baking, it's always wise to start with a thicker frosting and thin it out as needed. Thick frosting comes in handy in a variety of baking projects and applications. In order to build a structurally-sound layer cake, you'll want to use a thick, firmer buttercream in between your cake layers; this will give the cake height and keep it level. When decorating cookies, a firm royal icing is crucial to piping elegant, clean designs and fine lines.
While it's relatively easy to thin out your frosting—a bit of water, milk, or cream should do the trick—regaining body and thickness in your frosting is slightly more challenging. But don't worry: It's not impossible to thicken frosting. If your frosting has gone wrong for who knows what reason (from a hot kitchen to too much added moisture) and has devolved into a soupy mess, not to worry: We're here with a route back to fluffy frosting perfection.
Some of our techniques for thickening frosting call for added ingredients, like powdered sugar; others simply require time. We're giving you the complete lowdown on how to thicken frosting in a pinch, whether you're working with buttercream or royal icing. Keep these tricks in your back pocket for future baking mishaps.
How to Thicken Buttercream
When you are frosting a cake, it's crucial to work with buttercream that's reached the perfect consistency. If your frosting is too runny, it'll melt and slide all over the cake; if it's too thick, it won't spread easily. Think of building and frosting your layer cake as a construction process: You'll want to start by forming a solid base structure, then work from there. When building a cake, we start with a thick, firm buttercream, then as we move into decoration, we thin our frosting out with a little bit of heavy cream to make it more spreadable and viscous.
But if you're starting out with a frosting that's a little too thin and runny, don't fret: You can come back from this. There are a few different ways to thicken your frosting to ensure that your cake is sturdy, clean, and polished:
- Allow your frosting to sit in the fridge, covered with saran wrap, for 2 hours—this will help your frosting firm up.
- If the frosting still has not reached your desired thickness after chilling, add a few tablespoons of sifted powdered sugar to help your buttercream stiffen.
How to Thicken Royal Icing
If you're making royal icing, often used for decorating cookies, mixing to the right consistency is key to achieving clean, pretty lines and decorative features. You can learn all about the different consistencies of royal icing that we use for different purposes here, but the main distinction is between flooding-consistency icing (a looser icing used to fill in large surfaces) and piping-consistency icing (a stiffer icing used to pipe lines and intricate designs).
We always start with a firmer icing, then gradually add water to make it more liquid. To achieve a flooding-consistency icing, we add water—a couple tablespoons at a time—until the icing reaches a spreadable consistency. But what if you want to work the other way around, making the icing firmer rather than looser? We've all been there: You accidentally added too much water at the onset, making your icing far too runny for the piping bag.
Luckily, you have a few options for an easy fix:
- To thicken your royal icing, add more sifted powdered sugar—a couple tablespoons at a time—until the icing reaches your desired consistency.
- If you want to thicken your royal icing without adding additional sugar, you can add a very small amount of corn starch (around ½ teaspoon), which will help your icing thicken up.
- Allowing your icing time to rest and chill in the fridge can also help it gain more body—if it's not already in the piping bag, be sure to cover the bowl with saran wrap so the icing doesn't form a crust.