Icing sugar is a fine, powdered form of white sugar. Its texture is ideal for making icing and buttercreams as it dissolves quickly and easily and does not really require the application of heat.
Icing sugar comes in different grades according to how finely the sugar is milled, denoted by the number of Xs on the packet.
Icing sugar easily absorbs moisture and odours – keep in an airtight container in a cool, dark place. Unopened packets of icing sugar can be stored for up to two years.
Because of its fine texture, icing sugar has a tendency to lump together (despite the addition of anti-caking agents such as cornstarch in commercial varieties), so sift it before use.
Icing sugar can sometimes include wheat starch or cornstarch to keep the sugar soft and powdery, and so may not be suitable for coeliacs – check the packaging carefully before buying. Specialist bake shops may stock starch-free 'pure' icing sugar – as such, it may be lumpy and will require extra sifting before use. Pure icing sugar is preferred for making royal icing as the result will keep its shape better when piped or moulded.