Superfine sugar is granulated sugar that has been ground into finer crystals than regular granulated white sugar. Also known as caster sugar, it is popular with bakers because the smaller crystals cream very easily into butter and dissolve more readily into meringues and batters. This leads to products that have a finer crumb and lighter texture when finished, a result that is preferred by many bakers. Superfine sugar is specifically called for in recipes that are very light, such as meringues and angel food cakes.
You can substitute superfine sugar into recipes that call for granulated white sugar and get good results, but you will not necessarily get as good a result if attempting to substitute regular sugar into a recipe that calls for superfine sugar. This is because recipes that specify superfine sugar to be used often count on the fact that the sugar dissolves so easily to get the best finished product possible. If your local grocery store doesn’t carry superfine sugar – or baker’s sugar, as it is sometimes called on packaging – there is no need to worry because you can easily make your own by processing regular granulated sugar in the food processor until it is very fine. A minute or so is usually more than enough time to process the sugar and the newly chopped crystals will work just as well in recipes as store-bought superfine sugar.
Superfine sugar is not the same as powdered or confectioners’ sugar and the two types of sugar are not interchangeable. Confectioners’ sugar has been pulverized to a powder that dissolves almost instantly in liquids and will not incorporate into a recipe the same way that superfine sugar will.