Caster Sugar
Caster sugar (also spelled castor sugar) is a fine-grained white sugar, ground finer than regular granulated sugar but not powdered into dust. Common in British and Australian baking, it dissolves faster than granulated sugar, which makes it the standard choice for meringues, sponge cakes, mousses, and creamed butter-and-sugar mixtures where a smooth, even texture matters.
Varieties
Golden caster sugar is an unrefined version that keeps a trace of molasses, giving a light caramel note and pale gold color. It substitutes 1:1 for white caster sugar but will slightly darken batters and add a faint toffee flavor.
Buying tips
Look for bags labeled caster sugar or superfine sugar; in the US it's sometimes sold as baker's sugar. Check that the bag feels loose and pourable rather than clumped, which signals moisture exposure.
Substitutes
Granulated sugar, processed in a food processor — 1:1
Pulse regular granulated sugar for 20 to 30 seconds until it looks noticeably finer and slightly powdery at the edges. This is essentially how commercial caster sugar is made.
Superfine sugar (US) — 1:1
This is the American name for the same fine-grain sugar; if a US recipe or store label says superfine, it's a direct swap for caster sugar.
Regular granulated sugar, unprocessed — 1:1
Works fine in most cake and cookie batters where it's beaten with butter or dissolved in warm liquid, but expect a slightly coarser crumb and less volume in meringues.
Powdered (confectioner's) sugar — 3/4 cup per 1 cup caster sugar
Only use in a pinch for recipes without a delicate structure, like some cookie doughs. The added cornstarch can make cakes gummy and meringues won't whip properly.
Storage
Store in an airtight container or resealable bag at room temperature, away from moisture. Its fine grain means it can clump faster than granulated sugar if humidity gets in; a bay leaf or a few dry rice grains in the container helps keep it loose.
How to use
Best for meringues and whipped egg whites, where the fine grain dissolves fully and avoids a grainy texture. Also standard for creaming with butter in sponge cakes, whisking into custards and curds, and sweetening cold drinks or cocktails where quick dissolving matters.
What it pairs with
Works well anywhere a smooth dissolve matters: whipped cream, fruit macerated for shortcakes, meringue toppings on pies, and simple syrups for cocktails or soaking cake layers.
Nutrition
Nutritionally identical to granulated sugar, same calories and carbohydrate content gram for gram. The only difference is grain size, which affects texture and dissolving speed, not sweetness or nutrition.
FAQ
What's the actual difference between caster sugar and granulated sugar?
Grain size. Caster sugar crystals are noticeably smaller, which lets it dissolve faster in batters, meringues, and cold liquids where granulated sugar might leave a slightly grainy texture.
Can caster sugar replace powdered sugar in frosting?
No. Caster sugar won't dissolve into a smooth glaze or frosting the way powdered sugar does; it lacks the fine, dust-like texture and added cornstarch that give frosting its structure.
Is caster sugar the same as superfine sugar?
Yes, they're the same product under different regional names, caster sugar in the UK and Australia, superfine or baker's sugar in the US.
Can I make caster sugar at home?
Yes. Pulse regular granulated sugar in a food processor for 20 to 30 seconds until finer, then use it immediately or store in an airtight container.
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