How to Fix Curdled or Soupy Buttercream

Meringue buttercream almost always looks ruined at some point. Somewhere after you add the butter, the silky meringue turns into what looks like cottage cheese floating in liquid, or it slumps into a thin, greasy soup. Neither one means you need to start over. Both are temperature problems, and the fix is to move the temperature in the right direction while the mixer keeps running.

The trick is knowing which way you need to go. Curdled buttercream is too cold; soupy buttercream is too warm. A quick look, or better, an instant-read thermometer, tells you which, and a few minutes of warming or chilling brings the emulsion back together.

Diagnose before you act

Meringue buttercream is an emulsion of fat (butter) and water (from the egg whites), held together by whipping. When the butter is too firm, it cannot blend smoothly with the meringue and breaks into small hard pieces swimming in liquid. When the butter is too soft, it melts and cannot trap air, so the frosting turns loose and shiny.

An instant-read thermometer settles the question in seconds. Below about 18°C (65°F), expect curdling. Above about 24°C (75°F), expect it to turn soupy. If you have no thermometer, feel the outside of the bowl: cold and stiff points to curdling; warm points to soupiness.

• Lumpy, grainy, separated with liquid: too cold
• Thin, glossy, will not hold a peak: too warm
• Smooth but slightly soft: keep whipping a few more minutes

Fixing curdled buttercream

Keep the mixer running on medium. Warm the outside of the bowl briefly with a kitchen torch, a hair dryer, or a towel wrung out in hot water, for 10 to 20 seconds at a time. Watch the sides of the bowl: as the butter softens, the mixture suddenly turns smooth and creamy.

Another approach is to scoop out about a cup of the buttercream, melt it in the microwave in 10-second bursts until just liquid, and stream it back into the bowl while whipping. This warms the whole batch evenly without risking overheating one area.

Fixing soupy buttercream

Set the bowl in the refrigerator for 10 to 15 minutes, or in a larger bowl of ice water for a few minutes, until the edges are firm and the center is still soft. Then return it to the mixer and whip on medium-high. It may pass through a curdled stage briefly before turning smooth.

If it is still loose after whipping, chill for another 5 minutes and repeat. Avoid adding powdered sugar to thicken it; that changes the flavor and texture without fixing the underlying temperature problem.

Preventing it next time

For Swiss meringue buttercream, whisk the egg whites and sugar over simmering water until the sugar dissolves and the mixture reaches 71°C (160°F), the temperature FDA recommends for egg dishes, then whip until the bowl feels cool to the touch, about 8 to 10 minutes. For Italian meringue buttercream, whip until the hot syrup meringue has cooled the same way. Adding butter to a warm meringue is the most common cause of soupy frosting.

Cut the butter into tablespoon-size pieces and let it warm to cool room temperature, around 18 to 20°C (65 to 68°F). It should bend without cracking but not look shiny or greasy. Add it a piece at a time, and keep whipping after the last piece goes in; it often takes several minutes to come together.

Other buttercreams that split

American buttercream rarely curdles, but it can separate if you add cold milk, cream or lemon juice to soft butter. Warm the liquid slightly and add it gradually. Ermine frosting, made with a cooked flour and milk base, breaks if the base is warmer than the butter; cool the pudding base completely first.

Cream cheese frosting behaves differently. Overbeating breaks down the cream cheese and turns it runny, and no temperature trick reverses that fully. Chill it to firm it up, and next time beat the butter and sugar first, then mix in cold cream cheese briefly at the end.

Common questions

Can I make meringue buttercream ahead?

Yes. Refrigerate it airtight for up to about a week or freeze it for longer. Bring it to room temperature, which takes a few hours, then rewhip. It will curdle as it warms; keep whipping and warming gently until smooth.

My buttercream tastes too buttery. Is that related?

No, that is a flavor balance issue. A pinch of salt, a little more vanilla, or a spoonful of melted chocolate or fruit purée rounds out the flavor. Use a good unsalted butter, since meringue buttercream is mostly butter.

How long can a cake with meringue buttercream sit out?

These frostings contain eggs and lots of butter. Keep the finished cake cool and refrigerate it for longer storage, following the general rule of no more than about 2 hours at room temperature for perishable foods.