There are two common issues I hear about when making Swiss meringue buttercream. It is either curdled (looks “broken” or like cottage cheese) or soupy (looks like melted vanilla ice cream). This problem typically occurs after adding the butter to the meringue or when rewhipping the buttercream after cold storage in the fridge.
Swiss meringue buttercream is either soupy or curdled due to the temperature of the butter; it is either too warm or too cold. Both issues can be fixed either chilling or gently heating the buttercream. A slightly softened yet cool butter will bring the buttercream together and give it smooth texture for frosting cakes.
Now the key to knowing whether to heat or chill the buttercream is to look at the texture:
I will explain different ways to address each issue as well as the science behind each problem below.
By the way, if you’re more of a visual person, I walk you through it all in this buttercream video here:
Swiss meringue buttercream (SMBC) is a light and fluffy textured stable frosting. The “Swiss” in the name comes from the method in which we make the meringue - heating a sugar and egg white mixture and whipping until fluffy. Soft butter is then added to this meringue. This is how traditional Swiss meringue buttercream is made.
Now this is where it gets science-y. The stability (able to withstand high room temperatures and hold up heavy cake layers) comes from the fact that it’s an emulsion, which is a mixture of fat and water based ingredients. In our buttercream here, the butter is the fat ingredient and the meringue is the water-based ingredient.
Normally fat and water don’t like to mix . And even if you try to mix them, they will separate over time - think of shaking or whisking oil and water for a simple vinaigrette.
Swiss meringue buttercream, however, is stabilized (or prevented from separating) by something called an emulsifier. Think of emulsifiers as connectors - they have a really unique ability hold onto BOTH fat and water. This emulsifier, or connector, is located inside the butter, which is going to be important later on. ;)
Does your buttercream look like this? Kinda cottage cheese-y? Or broken?
This means that the butter is too cold. Remember how I said fat and water don’t like to mix? Well this is exactly what I’m talking about. When the butter is too cold, it forms these curds. That’s all the butterfat hanging out with each other.
You may see water too. That’s likely the meringue, which has deflated into a sugar syrup (but that’s normal and not an issue here).
The emulsifier - remember - they’re inside the butter? They’re stuck inside those cold firm curds and cannot connect to the meringue.
There’s a few ways to do it. No matter what method you choose, you want to heat it very gently until you just notice that the buttercream touching the insides bowl starts to just slide around. (Unless you’re using the microwave method, in which case just follow the instructions.)
Now place your buttercream back on the mixer and mix on low speed until the temperature is evenly distributed. It should take about a minute for the buttercream to come together, but if it seems like there’s still some cold pockets or chunky butter pieces, gently heat a little more and remix.
Does your buttercream look like this?
That means the butter in your Swiss meringue buttercream is too warm. Now you’ve likely formed a stable emulsion because it looks homogenous and not split.
The problem here is that the fat based ingredient (butter) is liquid.
In baking and cooking we can use butter in both its states: liquid and solid. For buttercream we want the butterfat to be a soft solid so that we can easily frost cakes and pipe with it. The ideal temperature I would say for these techniques is around 68-75°F/20-24°C degrees.
The timing will depend on the amount of buttercream you’re trying to make but start with 5 minutes. Sometimes all you need is to put a chill on the bowl but not the buttercream itself. In that way, it kind of functions like an ice cream maker, where you’re just mixing and eventually the bowl will chill the mixture inside if you slowly mix it.
Now place the chilled bowl back on your mixer and let it mix on low speed. You slowly start to see the thicker buttercream form along the interior of the bowl sides, then as it continually chills, the buttercream will thicken all together.
If it still seems soupy after about 5 minutes of mixing, try to chill it in the fridge for another 5-10 minutes. Be careful though, you don’t want to over-chill it to the point where the butter is a firm solid. No big deal if you do - just go do any of the gentle heating steps listed above this section.