Sweeteners

Caster Sugar (Superfine)

Ultra-fine white sugar that dissolves almost instantly, giving lighter meringues, smoother creamed batters, and grit-free custards.

Caster sugar — sold as superfine sugar in the United States — is plain refined sucrose milled to a grain finer than ordinary granulated. Each crystal sits roughly 0.35 mm across, between granulated (~0.5 mm) and powdered/icing sugar (~0.06 mm). Chemically it is identical to the bag of sugar most cooks keep on the shelf: the same sweetness, the same ~387 kcal per 100 g, the same browning power in the oven. What changes is kinetic. Smaller crystals expose more surface area per gram, so they dissolve faster in cold and room-temperature liquids, integrate more evenly into creamed mixtures, and leave no perceptible grain in custards and whipped cream.

That faster dissolution is the entire reason caster exists. In a meringue, any undissolved sugar crystals left suspended in the foam act as nucleation points for the syrup that beads up on the surface (bakers call it weeping). Finer crystals dissolve fully during whipping, giving a glossier, more stable foam. The same logic applies to a custard that will not be strained, cold lemon juice for a curd, a shaker full of ice and bitters, or macerated strawberries destined for Eton mess — anywhere the granular texture of ordinary sugar would be a real problem, caster is the clean answer.

Where crystal size is invisible after the bake, however, granulated is a perfectly fine substitute, and most recipes that call for caster work just as well with regular sugar swapped in 1:1 by volume. American 'superfine' and British 'caster' are direct equivalents; the only US watch-out is 'bar sugar', which is similar in grain but usually contains a small amount of cornstarch or dextrose as an anti-caking agent and is best reserved for cocktails rather than delicate baking.

Measured in: g
Storage: Pantry

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Types & varieties

British caster sugar

The UK/Ireland/AU/NZ standard; crystal size around 0.35 mm, designed to dissolve quickly in cold liquids and meringues

American superfine sugar

The direct US equivalent, sold under the 'Superfine' label by C&H and Domino; safe 1:1 swap for British caster

Baker's sugar

American trade name, sometimes even slightly finer than British caster; popular with commercial bakers for sponges and meringues

Bar sugar

Bartending-grade superfine sugar; often has a small amount of cornstarch or dextrose added to discourage caking — useful for muddling and shaken cocktails, not ideal for delicate baking

Vanilla caster sugar

Caster stored with a split vanilla pod (or a dab of vanilla paste) until fragrant; used as a flavored sweetener for dusting, biscuit doughs, and shortbread

DIY caster

Regular granulated sugar pulsed briefly in a clean, dry food processor or blender — a common kitchen workaround, not an industrial variety

Choosing a substitute when caster isn't on hand

Most baking can absorb granulated sugar 1:1 by volume with no detectable difference, so the substitution is worth thinking through only in a few situations. The right answer depends on what role the sugar is playing in the recipe.

For cold liquids — cocktails, fruit purées, lemon juice for curd — make a quick 1:1 simple syrup from granulated sugar, or pulse the dry sugar briefly in a clean dry grinder before adding
For meringue and pavlova, pulse granulated to caster texture; with straight granulated expect slightly slower whipping and a marginally less glossy result, but no real failure
For batters that will be fully baked (sponge, cookies, quick breads, muffins), straight granulated is fine — the crystals disappear into the crumb
Never substitute powdered/icing sugar 1:1; it is far finer and contains cornstarch, which can throw off structure, tenderness, and flavor
Fine sanding sugar is the right grain for decorating but its coating keeps it from dissolving into a surface; it is not a baking substitute

Common uses

Meringues, pavlovas, and Italian or Swiss buttercreams — finer crystals dissolve into egg whites more readily, reducing weeping and yielding a shinier, more stable foamSponge cakes and génoise — creams more easily with butter, trapping less air unevenness and producing a finer, more even crumbCustards, zabaglione, and pastry cream — eliminates grittiness when the custard is served without further straining or cookingCocktails — old-fashioneds, sours, and punches where granulated can sit undissolved at the bottom; this is what 'bar sugar' was developed forSorbets and granitas — dissolves in cold fruit purée without a grainy texture or the need for extended heatingMacerated berries and fruit salads — draws out juice quickly without leaving a sandy mouthfeel in the finished dishCaramel and dry caramel work — fine grains melt and color more evenly, with fewer stray coarse crystals scorching at the pan's edgeCreamed mixtures for buttercream and sweetened whipped cream — integrates without the brief grittiness that granulated can leave even after thorough beating

Tips & pitfalls

To make a DIY substitute at home, pulse granulated sugar in a clean, dry food processor for 10–15 seconds only; over-processing turns it into powdered/icing sugar, which behaves very differently and contains cornstarch in commercial form
Caster and granulated can be swapped 1:1 by volume in most baking — the small difference in weight is rarely meaningful
When substituting granulated for caster, expect slightly slower dissolution in cold liquids (cocktails, cold syrups) and a marginally grainier finish in unbaked custards; both are minor rather than deal-breaking
In the US, look for the word 'superfine' on the bag; 'caster' is rarely labeled in American supermarkets
Keep caster bone-dry — because the crystals are small and porous, it clumps faster than granulated when exposed to humidity; sift before measuring if it has set
In meringue, caster reduces weeping because any undissolved sugar crystals left in the finished foam attract moisture and release it as beads of syrup on the surface; finer crystals fully dissolve during whipping
Do not substitute caster where a recipe calls for granulated for deliberate texture — shortbread that should be slightly sandy, crumble toppings, or cookies that need a coarser crunch all depend on the larger crystal
For cocktails, if you only have granulated on hand, stir a quick 1:1 simple syrup and use that in place of bar sugar; it dissolves instantly and integrates cleanly into the drink

Nutrition

387kcal

Energy

1619 kJ · per 100 g

Where the calories come from

Protein 0%Carbs 100%Fat 0%

Protein

0% DV

Carbs

100g

36% DV

Fat

0% DV

Fiber

0% DV

Sugars

99.8g

of which

Sodium

1mg

0% DV

Notable micronutrients

Riboflavin (B2)1% DV

Selenium1% DV

Source · USDA FoodData Central · Sugars, granulated

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In the shops

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Good to know

Crystal size: Approximately 0.35 mm — finer than granulated (~0.5 mm), coarser than powdered/icing sugar (~0.06 mm)
Composition: Essentially pure sucrose (>99.9%); produced by milling standard refined cane or beet sugar to a finer grain
Regional naming: Caster or castor sugar in the UK, Ireland, Australia, and New Zealand; superfine, baker's, or bar sugar in the US and Canada
Origin of the name: British 'caster' refers to the small perforated castor shakers it was designed to flow through; American 'superfine' describes the grain
Clumping behavior: Bone-dry crystals with high surface area absorb ambient humidity quickly and clump faster than granulated; sift before measuring if lumpy
Shelf life: Indefinite if kept dry and sealed in an airtight container
Cost: Typically 10–25% more per kilo than standard granulated sugar
Calories: ~387 kcal per 100 g — identical to granulated and other white sugars

Substitutes

Granulated white sugar (1:1 by volume) — The most accessible substitute; identical sucrose content, but larger crystals dissolve more slowly in cold liquids and give a slightly grainier texture in unbaked custards and meringues
DIY caster (pulsed granulated) — Pulse granulated sugar briefly in a clean, dry food processor; stop the moment the crystals look finer — do not over-process or it becomes icing sugar
American superfine or baker's sugar — Direct commercial equivalent to British caster; safe 1:1 swap in any application
Fine sanding sugar — Fine enough in grain, but the coating prevents full dissolution into a batter; acceptable for decorating, not for baking into mixtures
Demerara or turbinado sugar — Not a true substitute — different color, flavor, and much larger crystals; only appropriate where those changes are wanted (coffee, oatmeal, some rustic cookies)
Coconut sugar — Texture and flavor diverge sharply; do not substitute 1:1 in delicate baking or anywhere the recipe assumes a neutral, fine white sugar
Liquid sweeteners (honey, maple, agave, golden syrup) — Not a structural substitute — will change moisture balance, browning, and flavor; reduce other liquids and adjust acidity if using