Granulated sugar
The default sugar, and coarser than caster — which matters wherever the sugar has to dissolve or trap air.
Also called white sugar (INTERNATIONAL); table sugar (INTERNATIONAL); regular sugar (US); sucrose (TRADE)
Granulated and caster sugar are the same substance — sucrose — at different crystal sizes, and the size decides where each works.
In anything DISSOLVED, they are interchangeable. A syrup, a wet batter, a bread dough: given liquid and time the crystals disappear and nothing distinguishes them.
In anything where the crystal does mechanical work, they are not. Creaming depends on sharp crystals dragging air into fat, and caster’s finer crystals do it more efficiently and more evenly — granulated creams adequately and takes longer, and leaves a slightly coarser crumb. In a shortbread or a delicate biscuit, undissolved granulated crystals are detectable as grittiness.
The practical rule is that granulated substitutes for caster with a little more beating in most things and not at all where the texture is fine and the mixture is dry.
What changes if it is left out
Caster sugar substitutes directly and slightly improves anything creamed. Icing sugar does not — it is powdered and contains anti-caking starch, so it dissolves instantly and traps no air, giving a denser result.
Follows from the crystal-size mechanism recorded on caster sugar and on creaming, both of which carry their own support.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
What it does
Aeration
Sharp crystals drag air into fat during creaming. Coarser than caster, so it does the job more slowly and leaves a slightly coarser crumb.
Covered in
The sugars, and when the difference matters
The same substance one grade coarser, which matters wherever the crystal does work.
Compared in
Caster sugar vs granulated sugar
One side of the comparison.