Powdered sugar

Powdered sugar, also called confectioners' sugar and icing sugar is a finely ground sugar produced by milling granulated sugar into a powdered state. It usually contains between 2% and 5% of an anti-caking agent—such as corn starch, potato starch or tricalcium phosphate^[1][2]—to absorb moisture, prevent clumping, and improve flow. Although most often produced in a factory, a proxy for powdered sugar can be made by processing ordinary granulated sugar in a coffee grinder, or by crushing it by hand in a mortar and pestle.