Recipes often specify caster sugar without explaining why, and reaching for whatever sugar is in the cupboard instead can quietly change the result.
What caster sugar actually is
Caster sugar is white refined sugar ground to a finer grain than standard granulated sugar, but not as fine as icing sugar. The name comes from the fine holes of a sugar caster, small enough for it to pour through easily. Golden caster sugar is the same fine grind but made from a less refined sugar that keeps a light, natural colour and a very subtle caramel note.
Why the grain size matters
Finer crystals dissolve faster and more completely, which matters most in recipes where sugar needs to disappear into a mixture quickly, like meringues, sponge cakes, and creamed butter mixtures. Standard granulated sugar takes longer to dissolve and can leave a slightly gritty texture in delicate bakes, while caster sugar blends in smoothly.
Caster sugar versus white granulated sugar
They are chemically identical, both are refined white sugar, the only difference is crystal size. In recipes where sugar has time to dissolve, like a stirred sauce or sweetened coffee, granulated works fine as a substitute. In recipes relying on quick, even dissolving, like whisking egg whites for meringue, caster sugar gives a noticeably better result.
Caster sugar versus demerara
Demerara is a different category entirely, an unrefined cane sugar with large crystals and a natural caramel flavour, closer in character to golden caster than white caster but coarser in texture. Demerara suits toppings and drinks where texture and flavour matter, caster suits bakes where smooth dissolving matters most.
Substituting in a pinch
- No caster sugar: pulse granulated sugar briefly in a food processor to approximate the finer grain
- No golden caster sugar: standard caster sugar works, you will just lose the light caramel note
- No white sugar at all: caster sugar substitutes directly in most recipes calling for granulated
