Caster sugar, also known as castor sugar or superfine sugar, is a type of fine granulated sugar that is commonly used in baking recipes in many parts of the world, including the UK, Australia, and New Zealand. It is finer than regular granulated sugar, but not as fine as powdered sugar. Caster sugar dissolves more easily than granulated sugar, making it ideal for recipes that require a smooth texture, such as meringues, mousses, and whipped cream. It is also used as a sweetener in beverages, including cocktails and mocktails.
In the US, caster sugar is known as superfine sugar, bakers sugar, or bar sugar. If you cannot find caster sugar in your local grocery store, you can make it yourself by blending granulated sugar in a blender or food processor for a few minutes until it becomes super fine, but not powdery. Caster sugar is not the same as powdered sugar, which is even finer and often mixed with starch to prevent clumping.
