What Is Caster Sugar and What's a Good Substitute?

Here’s what to know about the British baking ingredient. 

If you've ever baked with a British cookbook, you've likely noticed that many of the recipes call for caster sugar instead of granulated sugar. What is this mystery ingredient — and what's the best substitute for American bakers? Here's everything you need to know:

What Is Caster Sugar?

edited sugar for simple syrup photo by Leslie Kelly
Leslie Kelly

Caster, or castor, sugar is a type of fine granulated sugar that's widely available in the United Kingdom. It's not quite as common in the United States, though you can find it in some baking aisles under the name "superfine sugar." Its texture is somewhere between regular granulated sugar and confectioners' sugar. What's with the name? Years ago, this type of sugar was often found in a shaker (called a caster) and sprinkled on fresh fruits.

White vs. Golden Caster Sugar

Caster sugar is available in two varieties: white (regular) and golden. The golden variety is unrefined and processed in a way that maintains some of the molasses, similar to brown sugar. It has a warmer, more caramel-like flavor than white caster sugar.

Caster Sugar Uses

Meringue Cookies

Since it's finer than granulated sugar, caster sugar dissolves and incorporates more quickly — this makes it perfect for light and airy desserts like meringues and soufflés. It's also often used to sweeten beverages, such as tea, because it doesn't need heat to dissolve. Really, though, caster sugar can be used in almost any way granulated sugar is used.

Caster Sugar vs. Granulated Sugar

Granulated sugar has a larger and coarser grain than caster sugar. Though they can generally be used interchangeably, granulated sugar does not incorporate into batters as quickly. Cakes and other desserts baked with granulated sugar instead of caster sugar sometimes have a speckled appearance due to the undissolved granules.

Caster Sugar vs. Powdered Sugar

Russian Tea Cakes I sprinkled with powdered sugar
Philly Ry

Powdered, or confectioners', sugar is finely ground granulated sugar that has been mixed with a small amount of cornstarch to prevent clumping. It's commonly found in frostings and icings or dusted over desserts. Powdered sugar is finer than caster sugar, and the two are usually not interchangeable.

Caster Sugar Substitute

Adding Sugar to Whipped Cream
Photo by Meredith. Meredith

Granulated sugar will usually work just fine as a caster sugar alternative. Substitute on a 1:1 ratio (if your recipe calls for a cup of caster sugar, use a cup of granulated sugar).

If you're using granulated sugar in a cake or cookie recipe that calls for caster sugar, use this tip: Start with slightly colder than room temperature butter, then cream the butter and sugar for longer than you normally would. This gives the ingredients time to incorporate.

If you're making a meringue, meanwhile, mix granulated sugar and egg whites at a low speed. This gives the sugar ample time to dissolve.

Simply sugar
MichellePatrickPhotographyLLC/Getty Images

How to Make Caster Sugar

The best substitute is DIY caster sugar. Make the British ingredient at home with just granulated sugar and a food processor, blender, or coffee grinder. To make caster sugar, simply pulse or blend granulated sugar until it reaches a finely ground — but not powdery — consistency. Two or three quick pulses will usually do the trick.

Where to Buy Caster Sugar In the U.S.

Bakers located in the U.S. may be able to find superfine sugar on grocery store shelves, but will likely have to visit a specialty store or order the ingredient online.

Judee's Superfine Caster Baker's Sugar

Caster sugar

Caster Sugar Storage

Store caster sugar in the same way you'd store granulated sugar: In an airtight container in a cool, dark place. Sugars do best at room temperature, so don't worry about keeping it in the fridge.


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