When our Baking Club focused on Yotam Ottolenghi and Helen Goh's cookbook "Sweet: Desserts from London's Ottolenghi," members with the UK version kept noticing that the vast majority of the recipes call for caster sugar.
Caster sugar goes by a variety of names, including castor sugar, baker's sugar, and superfine sugar, the last of which alludes to what exactly it is: a finer granulated sugar. If a grain of granulated sugar is big and a grain of powdered sugar is tiny, caster sugar would be somewhere in between.
What is caster sugar?
Caster sugar goes by a variety of names, including castor sugar, baker's sugar, and superfine sugar, the last of which alludes to what exactly it is: a type of superfine sugar. Like if regular old white sugar got put into the food processor for a minute or two. If a grain of granulated sugar is big and a grain of confectioners' sugar is tiny, caster sugar would be somewhere in between. It's ideal for dissolving in ice cold beverages (like some added sweetness for an iced coffee or iced tea), as well as seamlessly blending into frosting, glazes, and whipped cream. Caster sugar brings plenty of sweetness without any of the textural graininess that coarser types of sugars often contribute. There's a chance you'll find caster sugar in some regular grocery stores, but any specialty baking shop or big-box online retailer is guaranteed to carry it.
As for how it compares to other types of sugar, it's not as fine as powdered sugar aka icing sugar aka confectioners' sugar. Whereas those types of sugar are true powder (closer to cornstarch or flour), caster sugar still has a grain-like texture that you can feel between your fingers.
Types of caster sugar
Just like regular granulated sugar and brown sugar, you'll find both white caster sugar and golden caster sugar. Golden caster sugar is made with natural, unrefined cane sugar, whereas regular caster sugar is refined for that pure white color. You can use them interchangeably…for the most part. Think of them, again, as superfine versions of regular sugar and brown sugar. They'll work as seamless substitutes for one another in cake and cookies, but you probably wouldn't use brown sugar in a recipe for vanilla buttercream; same goes for golden caster sugar.
After learning about the difference between regular granulated sugar and caster sugar, Food52's community member Eliza Triggs made back-to-back batches of Ottolenghi and Goh's Cranberry Almond Cookies and found that using caster sugar did make a noticeable difference in the appearance and taste:
The iced cookie on the bottom is made with regular sugar; it looks and tastes drier and denser (although it's definitely a tasty biscuit). The one on the top is made with caster sugar, and (although it's still crumbly) is softer, lighter, and more buttery.
Helen Goh explained that caster sugar appears in so many of the recipes in Sweet because: "In the UK, we use it for most baked goods, especially if it is being creamed/beaten with butter for making cakes, or for whisking with egg whites for meringues."
While caster sugar is readily available in the UK, Baking Club members in the United States have had trouble locating it, and when they can get their hands on it, they find it is priced much higher than regular granulated sugar. Luckily, Goh provided the group with three strategies to still get optimal outcomes in their baked goods. Here's how to achieve the best baked goods with caster sugar.
How to bake with caster Sugar
1. Start with cooler than room temp butter.
Goh explains that if you are creaming sugar with butter (for cakes or cookies, for example), starting with firmer butter allows you to cream the two together for a bit longer without it turning greasy, adding:
Over-creaming can result in an oily, dense cake because the butter has essentially melted. Similarly, under-creaming can result in a dense, dry cake, because the butter and sugar have not had enough air incorporated into it, and the sugar granules remain large, so the cake/crumb will be coarse and heavy.
2. Whisk egg whites on a lower speed.
If you're combining sugar and egg whites for something like a meringue, Goh suggests whisking the egg whites and granulated sugar together on a slightly lower speed so the sugar granules have more time to dissolve, adding:
One of the ways you can tell if your meringue is ready for the oven is if you can barely feel the sugar granules between your thumb and forefinger. I have seen a few 'speckled' pavlovas which look like undissolved sugar granules.
3. Make your own caster sugar.
You can also skip the workarounds and cut to the chase by making your own caster sugar. Simply process regular granulated sugar in a food processor, high-powered blender, or (clean) coffee grinder until the sugar granules are smaller. (Just keep an eye on it — if you process it too long you'll end up with homemade powdered sugar instead.) Goh notes that the granules won't be as uniformly sized as the store-bought variety, but says that it will work fine.
Once you've made a batch of caster sugar, here are a few recipes to put it to good use:
Caster sugar recipes
Combine lemon meringue pie and a pavlova and a layer cake and you end up with something like this. We love the combination of lemon curd and pistachio-y yogurt. Note: It's a hefty project — but well worth it.
A last-minute two-ingredient host gift (or a party trick for the next time you have people over). All you need are caster sugar and Angostura bitters. We'll bring the champagne.
Yes, toast can and should be called dessert. Do as Nigel Slater does and mash raspberries into oblivion, swirl these into sweetened whipped cream, and plop this cloud on just-toasted bread. In lieu of raspberries, try strawberries, blackberries, peaches, or apricots.
It's called lazy for a reason. To make the filling, you add a whole Meyer lemon (yep, rind, pith, and all), sugar, butter, vanilla, and eggs to a blender. Pour this into a tart shell and bake up your new go-to dessert.
Picture this: Espresso cake layers. Crispy-marshmallowy meringue. Maple syrup–sweetened whipped cream. Serve at the next gathering when you want to dazzle all your friends.
A sticky, dense almond cake gets upgraded with pomegranate molasses, then topped with sweetened mascarpone and fresh pomegranate seeds.
White rum, freshly squeezed lime juice, sugar, and ice, blended until slushy and frosty, equal as refreshing a cocktail as any heatwave could hope for. Serve in a glass that makes you smile, with a lime wheel on top.
Just when you thought crême brûlée couldn't be improved upon, it relocates to a flaky pie crust. Sprinkle sugar on top, then torch until your whole kitchen smells like caramel and toffee.