What Is Caster Sugar? Everything You Need to Know

Caster sugar is a staple in many British baking recipes. If you’re a seasoned baker (or a fan of The Great British Bake Off), you may already be familiar with it. In the U.S., however, caster sugar isn’t as common, so if it’s new to you, don’t worry! We're here to explain what it is, how to use it in your baking, and what the best alternatives are.

What Is Caster Sugar?

What exactly is caster sugar? It's simply granulated sugar that has been ground more finely. The finer texture of caster sugar allows it to dissolve more quickly than regular granulated sugar. This makes it a great choice for recipes like cocktails, mousses, and whipped cream where quick dissolution is key. While caster sugar is finer than granulated sugar, it's still coarser than powdered sugar, and each type has its ideal uses. In the U.S., caster sugar is not always easy to find at regular grocery stores. If it's unavailable, look for superfine sugar as an alternative. Additionally, both white and golden caster sugars are interchangeable, though golden caster sugar has a subtle caramel flavor due to being made from unrefined cane sugar, while white caster sugar is made from refined sugar and has a cleaner taste.

Caster Sugar Compared to Granulated Sugar

Caster sugar is more finely ground than granulated sugar, which allows it to dissolve with ease. While granulated sugar can still be used in baking, professional bakers prefer caster sugar because it blends effortlessly into cake batters, meringues, and similar recipes. While both sugars are often interchangeable, caster sugar is preferred for certain applications.

Caster Sugar vs. Confectioners’ Sugar

Confectioners’ sugar is ground far finer than caster sugar, transforming it into a soft powder. This super-fine sugar is commonly used for glazes, icings, and for dusting baked goods with a snowy appearance. To prevent clumping, confectioners’ sugar is often mixed with cornstarch, while caster sugar is purely sugar without any additives. These two sugars are generally not interchangeable.

How to Use Caster Sugar in Cooking

You can use caster sugar just like granulated sugar, with the added benefit of it dissolving more quickly. Try whisking it into a peanut sauce for a Peanutty Soba Noodle Salad, or use it to create a sugary rim for Spicy Jalapeño-Mint Margaritas. If you want to test its baking potential, swap granulated sugar for caster sugar in recipes like Pumpkin Cream Puffs, Pine Nut Drops, or Marbled Pound Cake—your options are limitless.

Caster Sugar Substitutes

If you can’t find caster sugar at the store and don’t have any on hand, there are several excellent substitutes you can use instead.

Granulated Sugar

Granulated sugar is the most reliable and easily accessible substitute for caster sugar, and it can be swapped in a 1:1 ratio. If you find granulated sugar too coarse for your recipe, try briefly processing it in a food processor to achieve a finer texture that will more closely resemble caster sugar.

Brown Sugar

Brown sugar may occasionally be used as a 1:1 replacement for caster sugar, but only in certain recipes. It adds moisture and a molasses flavor, making it ideal for rich, sweet treats like brownies and chocolate chip cookies, though it might not be suitable for all dishes.

Confectioners’ Sugar

While it's best to avoid using confectioners’ sugar as a substitute for caster sugar in baking, it can be an appropriate 1:1 replacement in recipes like frosting, whipped cream, and fruit sauces. Keep in mind that confectioners’ sugar often contains cornstarch, which can alter the texture of your dish.