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What Is Caster Sugar?
What it's called in the US: American recipes rarely say "caster sugar" — it's a British and Australian term. In the US, look for superfine sugar, baker's sugar, bar sugar, or the brand name Baker's Special. They are the same product.
The name comes from the "caster" (or castor) — the small shaker used to sprinkle fine sugar at the table.
How it compares to other sugars
| Sugar | Texture | Contains starch? | Best for |
|---|---|---|---|
| Granulated | Standard crystals | No | Everyday baking, creaming |
| Caster / superfine | Fine crystals | No | Meringues, sponges, cocktails, custards |
| Powdered / icing / confectioners' | Ground to a powder | Yes — cornstarch added | Icings, frostings, dusting |
Is caster sugar the same as powdered sugar? No — this is the most common confusion. Powdered sugar is ground much finer, to an actual powder, and almost always has cornstarch mixed in to prevent caking. That starch changes the texture and taste of a recipe, so they are not interchangeable. Substituting powdered sugar for caster sugar in a sponge or meringue will give you a dense, gummy, or chalky result.
Why recipes call for it: In meringues and soufflés, sugar has to dissolve completely into whipped egg whites — undissolved granulated crystals cause weeping and a grainy texture. In sponge cakes and shortbread, the fine crystals produce a lighter, more even crumb. In cocktails and cold drinks, it dissolves without stirring forever.
How to make caster sugar at home (it takes about a minute):
- Measure slightly more granulated sugar than the recipe needs — you'll lose a little to the sides of the machine.
- Add it to a food processor, blender, or clean spice grinder.
- Pulse for 20–60 seconds, until the crystals are noticeably finer but still sandy — not a powder.
- Let the dust settle before opening the lid, then re-measure by weight or volume, since grinding changes how it packs.
Substituting
- Granulated → caster: substitute 1:1 by weight, and grind it as above if the recipe depends on fast dissolving (meringue, mousse, cold drinks). For most cakes and cookies you can get away with plain granulated sugar and a longer creaming time.
- Powdered → caster: avoid. If you're stuck, use about 1¾ cups powdered per 1 cup caster and expect a different texture.
Golden caster sugar is the unrefined version — same fine crystals, but with a light caramel colour and a subtle toffee note.
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