Fillings, icings and creams
Buttercream, royal icing, fondant, pastry cream and the rest: what sets each one, and why the same complaint means different things in each.
One complaint, three different answers
Grainy buttercream is sugar that never dissolved — dissolve it. Grainy fondant is sugar that dissolved and then crystallised out again — stop it doing that. Grainy whipped cream is fat that has begun to coalesce, and it is about twenty seconds from being butter with no way back.
The same word, three mechanisms, three corrections. That is why these pages are grouped by how each preparation sets rather than by what goes into it — and it is why the diagnosis asks which one you have before it offers a cause.
Solid fat
Soft when warm, firm when cool, and reversible in both directions. Nearly every problem with one of these is a temperature problem, and nearly every fix is too.
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.
and an emulsionCream cheese frosting
A much wetter system than a butter icing, which is why the standard advice for a runny batch — add more icing sugar — eventually makes it worse.
and an emulsion
Sugar drying out
These set because water leaves them. The room is part of the recipe: they dry fast in dry air, refuse to set in damp air, and can soften again months later.
Royal icing
Icing sugar and egg white that sets by drying rather than by cooling or cooking — which is why humidity, not technique, is usually what went wrong.
A stabilised foam
Air held in a film that is stiff enough not to drain — for a while. The least stable things here, and the two that cannot be recovered once they are overworked.
Meringue
Egg white foam stabilised by sugar, in three versions with quite different stability — and the ingredient that ruins all three is fat.
and protein settingWhipped cream
Making whipped cream and making butter are the same process stopped at different points, which is why over-whipping cannot be undone.
Gelatinised starch
Thickened by starch that has swollen and gelled. The only group with a failure that shows up hours after you finished.
Pastry cream
A starch-set custard with a delayed failure mode: an enzyme in the yolks digests the starch overnight unless the cream was genuinely boiled.
and protein setting
Also here
Fondant
One word for two different substances — a crystallised sugar syrup and a kneaded sugar dough — which is why the advice a reader finds so often does not match the thing in front of them.
Ganache
Chocolate and cream held as one phase — an emulsion that firms as its cocoa butter crystallises, and splits when the balance of fat and water goes wrong.
What is deliberately not here
There is no glaze page. The search demand for the word is real and it is almost entirely about glazing hams, gammon and pottery — so a baking glaze page built to catch it would be answering a question nobody asked us. There is no separate custard page either: a pouring custard is set by egg alone and pastry cream explains where the two diverge, which is more useful than a near-duplicate.