Buttercream
Fat holding air and, in most styles, water — which is why almost everything that goes wrong with it is a temperature problem rather than a mixing one.
What makes it set
Solid fat, and An emulsion
A baked product is set by the oven. This one is not — and what sets it instead decides almost everything that can go wrong with it. See the whole family by mechanism.
Also called butter icing (UK), butter cream (INTERNATIONAL), swiss meringue buttercream (INTERNATIONAL) — One of several styles. It behaves differently from the icing-sugar kind and the page says how., italian meringue buttercream (INTERNATIONAL)
Buttercream is butter beaten with sugar until it holds air, and then — in every style except the simplest — with water in some form as well. It firms in the fridge and softens in a warm room for exactly the reason butter does, because it mostly is butter: the structure is a network of fat crystals, and that network exists only within a range of temperature.
The word covers at least four preparations that fail differently. The simplest beats icing sugar straight into softened butter; the sugar never dissolves, so its crystal size is the finished texture. The meringue styles beat butter into a whipped egg-white foam — Swiss heated over water, Italian cooked with a hot syrup — and are genuine emulsions, silkier, less sweet, and prone to splitting when the two halves are at different temperatures. A French style uses yolks instead of whites. A German or custard style beats butter into a set pastry cream.
Knowing which one is in the bowl is not pedantry. It decides whether a gritty texture is fixable, whether a split is recoverable, and whether adding more icing sugar will stiffen it or ruin it.
American usage calls all of this frosting, and calls several things that are not buttercream frosting too — cream cheese frosting and the cooked flour kind among them. BakeHQ does not treat the two words as equivalent for that reason: a page claiming to answer every frosting question would be answering some of them about the wrong substance.
What holds it together
A fat-continuous system: solid butterfat holding air cells, with sugar either dissolved into a water phase dispersed through it or suspended in it undissolved. The fat crystal network carries the structure, so the buttercream is as firm as its butter is at that moment and no firmer.
Follows from BakeHQ's fat plasticity record, which carries the citations for the crystal-network account of solid fat behaviour.
RecordedFollows from evidence recorded elsewhere on BakeHQ
What temperature does to it
The single variable that explains most buttercream failures. Below its plastic range the butter is too hard to beat air into and the mixture looks curdled and stiff; above it the crystal network fails, the air escapes and any water phase separates, so the buttercream goes soupy and looks curdled in the opposite direction. Both states look wrong in a similar way and need opposite corrections.
No temperature figures are given, deliberately. A fat's plastic range depends on its crystal composition and BakeHQ publishes no solid fat content data for any specific butter.
RecordedFollows from evidence recorded elsewhere on BakeHQ
How it keeps
Keeps at cool room temperature for a day or two and in the fridge for a week or so, but comes out of the fridge hard and has to be brought back to temperature and re-beaten before it will spread. A meringue-based buttercream contains egg white that has been heated; a raw-yolk French style has not, and is the one to treat as perishable.
Domestic practice rather than a measured shelf life, which would depend on formulation, water activity and storage temperature — none of which BakeHQ models.
RecordedEstablished practice, not a measured result
What a good one is like
- Texture
- Smooth and light on the tongue, with no perceptible grain
- Structure
- Holds a piped edge at room temperature without slumping
- Flavour
- Tastes of butter first; sweetness should not be the only note
Where it stops
A buttercream is a fat, and it behaves like one in every situation where that matters. It will not hold its shape in a warm room however it is made, and no stabiliser changes that — the fat is either below its plastic range or it is not. It cannot be made low-fat and still work, because the fat is the structure rather than the richness. And it is the wrong finish where a hard, cuttable surface is wanted: that is a sugar-set icing's job.
Which buttercream is in the bowl, and why it decides the answer
The four styles are not interchangeable and they do not fail in the same way.
THE ICING-SUGAR KIND — butter beaten with sifted icing sugar, sometimes with a splash of milk — is the sweetest and the least stable in the mouth, because the sugar is suspended rather than dissolved. It is also the most forgiving: there is very little water in it, so there is very little emulsion to break.
THE MERINGUE KINDS dissolve the sugar in the whites before the butter goes anywhere near them. Swiss heats whites and sugar together over water until the sugar is gone, then whips; Italian whips the whites and pours in a hot syrup. Both give a silkier, markedly less sweet result, and both split readily — not because they are delicate but because they are emulsions, and an emulsion built from a cool foam and warm butter has two phases at different temperatures.
THE FRENCH KIND uses yolks rather than whites and is richer, softer and yellower.
THE CUSTARD OR GERMAN KIND beats butter into a set pastry cream, which means it inherits pastry cream's problems as well as buttercream's — including the one where it liquefies overnight because the cream was never boiled.
Why more icing sugar is not a thickener
The commonest piece of advice given to somebody with a loose buttercream is to add more icing sugar, and in the icing-sugar style it does work, because the sugar is a solid suspended in fat and adding solids stiffens a suspension.
In any style with a real water phase it works up to a point and then reverses. Sugar dissolves in water, and a saturated sugar solution is a syrup rather than a solid. Past the point where the available water is saturated, more sugar makes the mixture sweeter and eventually looser rather than firmer — and it cannot be taken back out.
The reliable lever in every style is temperature. Cold firms a buttercream because it firms the fat; that is the whole mechanism, and it is reversible in both directions.
Related
Things that go wrong
Buttercream is runny, split or grainy
Both of its causes are properties of buttercream itself — the temperature of the fat and whether the sugar dissolved — rather than of anything it is put on.
Used on and in
The finish the format is built around — a cupcake is sized so that one swirl is the right ratio of icing to cake.
Used thin, because a filling firm enough to pipe would crack the sponge as it was rolled.
The layer filling, where the fat also slows the crumb drying out at the cut surface.
What it is built from
Not merely the flavour — the fat crystal network IS the structure, which is why the icing is only ever as firm as the butter is.
Its fineness is the whole reason it is specified: sugar suspended in fat cannot dissolve, so the crystal size is the finished texture.
The science behind it
Fat plasticity and crystal structure
The plastic range is the whole of the temperature story: too cold to hold air below it, unable to hold structure above it.
Commonly confused with
Called “frosting” interchangeably in American usage, and the water the cream cheese brings makes them behave differently enough that the same fix does not work on both.
Keep reading
Royal icing
Sets by sugar drying out rather than by solid fat, which is why the same complaint means something different in each.
Buttercream is runny, split or grainy
Work through what you can actually observe, rather than a list of possibilities.
Fillings, icings and creams
The whole family, grouped by what sets each one.