Caster sugar means fine crystals
Caster sugar is commonly called superfine sugar in the United States. Its crystals are smaller than ordinary granulated sugar, helping it dissolve readily in applications such as egg foams. It is not powdered or confectioners’ sugar.
King Arthur suggests finely processing granulated sugar as a substitute and using it by weight. Check the original recipe’s method and any specific substitution note before changing the sugar.
Three names to distinguish
Granulated sugar: ordinary crystals, with size varying by product.
Caster or superfine sugar: smaller crystals, useful when easy dissolving matters.
Powdered or icing sugar: a fine powder, often with added starch, used for different purposes.
A practical purchasing check
Read the package name rather than assuming a small bag near the decorating supplies contains the right sugar. If the recipe uses grams, preserve the stated weight. Grinding a product changes how it fills a measuring cup, so a volume shortcut can create an unnecessary second difference.
When dissolving matters
For meringue or a delicate foam, follow the source recipe’s gradual addition and mixing sequence. Selecting finer sugar does not remove the need to follow the method. For a simple batter that explicitly allows ordinary granulated sugar, there may be no reason to process it.
Write down which sugar you used when comparing results. A product-name note is more useful than describing both alternatives simply as white sugar.
Make superfine sugar without making icing sugar
Process granulated sugar briefly until its crystals are finer, then measure the finished sugar by weight. Stop while it remains granular; powdered sugar is a different product and may contain starch.
A concrete example appears in Sally’s French macarons: process 80 g granulated sugar with roughly 10–15 pulses, then weigh 80 g of the processed sugar for that formula. Pulse counts depend on equipment, so inspect the granules rather than turning that example into a universal timer. Do not add the cornstarch used in a homemade confectioners’ sugar blend.
Sources & scope
Reference synthesis and arithmetic where indicated. No first-hand kitchen testing is claimed.
- A guide to different types of sugars, how to use them, and when to substituteKing Arthur Baking · Accessed 2026-10-10
- French macarons guideSally’s Baking · Accessed 2026-10-06