Different types of sugar offer different properties in baking. Icing sugar and caster sugar are different types of sugar, used in different parts of the baking process.
It is not advisable to use icing sugar instead of caster sugar. That’s because the two have different coarsenesses, and because icing sugar has an extra little ingredient that makes it more unsuitable for the baking process.
What Is Caster Sugar?
Caster sugar, also known sometimes as castor sugar or superfine sugar, is used because it dissolves easily in the baking process, and because it has a soft, light texture to it.
The granules are slightly smaller than what is found in granulated sugar (the type that you’d buy to pop in your cup of tea).
Caster sugar is often used in recipes for all kinds of sweet baked goods, such as cupcakes and cakes, muffins, biscuits, and cookies. It is also used in meringues and soufflés.
What Is Icing Sugar?
Icing sugar, also known as confectioner’s sugar, bar sugar and powdered sugar is, as the name suggests, powder-like in nature.
It is incredibly fine, small particles of sugar, used in the finishing part of the baking process. Recipes that call for some sort of buttercream or iced frosting will often include icing sugar.
Icing sugar contains something other than just sugar, which is why it is not a suitable substitute for caster sugar: an anti-caking agent. This is often noted on the packaging as cornflour or maize starch, and this is what makes icing sugar a poor substitute for caster sugar.
What Will Happen if I Use Icing Sugar Instead of Caster Sugar?
Because of the anti-caking agent, icing sugar will not blend or mix the same as caster sugar in a baking recipe. The fine powder will clump together, causing sugary lumps in whatever you’re making.
The texture and consistency of the baked mix will change if you use icing sugar instead of caster sugar, too. Caster sugar is easier to whip or beat, causing firmer mixes. Icing sugar will leave things slightly runnier and clumpy.
What Can I Use Instead of Caster Sugar?
If you have a blender at home, you can create DIY caster sugar by blending granulated sugar, the type that you would mix into your cup of tea. Caster sugar is virtually a finer version of granulated sugar.
If you don’t have a blender, you can put some granulated sugar into a freezer bag, close it securely it, and then beat it with a rolling pin.
Alternatively, you can simply use granulated sugar as a substitute for caster sugar without grinding or blending it down first. You may need to use a little bit extra, however. And with meringues, you will need to beat more slowly.
Kim is a writer with more than a decade of experience, and a food enthusiast. When she’s not spending her time writing about her favourite dishes, you can find her in the cake aisle of her local supermarket, or making a mess in the kitchen.