How Do You Store Royal Icing?

You pipe icing or frosting if you only want a sugary flourish on your cookie or cake. If you want a more complex design than frosting scallops made with a spoon, however, that usually calls for royal icing: A variation which hardens after it cools down and keeps whatever fancy shape you molded it into. Regular old icing is typically a simple mixture of (lots of) powdered sugar and milk, but that thicker royal icing is typically made from (lots of) sugar and egg whites. Modern recipes commonly say to whip it up with meringue, which is egg whites and typically caster sugar or superfine sugar.

Eggs and milk are not known for their longevity, and leftover royal icing made with fresh eggs only lasts three days at room temperature, even if sealed. If you used meringue powder instead of fresh eggs, then royal icing can last closer to a couple of weeks at room temperature, so long as it's kept in bowl tightly covered with plastic wrapping. If you put that plastic-wrapped bowl into the fridge, then it should last up to a month (again, assuming you used meringue powder). If it puffs up or sours, it's spoiled.

All of that assumes you have a full, leftover batch of royal icing than you intend to pipe onto a dessert in the future. What if you've already made sugar cookies with intricate doodles on them? To store decorated cookies with royal icing, similarly seal them in a plastic-wrapped bowl, but they may only last about five days to a week before the cookies themselves begin going stale. They'll taste best within those first few days, though.

If you've decorated a cake with royal icing, that's much harder to wrap up in plastic without ruining the design. Instead, you want to let it sit in the fridge until the royal icing has completely gone solid. Then it's safer to wrap it up or place it in a solid container, where it should last a week in the fridge. If you think you might need these leftovers for longer, then it's also possible to freeze your cake or cookies, or even just the icing itself. Tightly seal them first, as always — batches of royal icing should be stored in resealable bags. In the freezer, cookies and cakes last about three months and pure royal icing lasts up to four to six months.