How to Make Royal Icing

1. Combine meringue powder with water in the bowl of a stand mixer, following the ratio printed on the can, and whip on low until it forms a soft, slightly foamy consistency, similar to the start of a meringue.
2. Add powdered sugar gradually, a cup or so at a time, mixing on low speed between additions so the sugar does not cloud the kitchen in a fine dust.
3. Once all the sugar is in, increase to medium-high speed and whip until the icing holds a stiff peak and looks matte and opaque rather than glossy. This is piping consistency, thick enough to hold sharp lines and lettering.
4. For flooding, thin a separate portion with water, a few drops at a time, until a spoon drizzled across the surface disappears back into the icing within about 10 to 15 seconds. This is a common working test in cookie decorating, not a fixed rule, and different decorators judge it by eye at slightly different speeds.
5. Divide and color as needed with gel paste before piping, since royal icing takes color the same way buttercream does, in small amounts with time to bloom.
6. Keep the working bowl covered with a damp cloth or plastic wrap pressed to the surface whenever you are not actively using it, since royal icing begins forming a dry skin quickly once exposed to air.
7. Pipe an outline first with the stiffer consistency, then flood the center with the thinned icing, letting it settle and self-level before it sets.

Piping consistency is stiff enough to hold a sharp, three-dimensional line when piped through a small round tip, useful for outlines, lettering and detail work that needs to keep its shape as it dries. Flooding consistency is thinned with a small amount of water until it spreads and self-levels into a smooth, flat surface inside a piped outline, which is the technique behind flat, glossy cookie decorating. Both come from the same base batch; flooding icing is simply the stiffer piping icing loosened with water added a few drops at a time.

Getting the flood consistency right takes some trial runs, since a batch that is too thin runs over the piped outline before it sets, and one that is too thick leaves visible ridges and peaks instead of a smooth surface. Testing a small amount on a spare surface before committing to a full batch of cookies is worth the extra few minutes.

Meringue powder is dried, pasteurized egg white, treated with heat during processing to reduce the risk that raw egg carries. Traditional royal icing recipes call for whipping fresh raw egg white directly with powdered sugar, and that egg white never gets cooked at any point in the process, since royal icing simply air-dries rather than baking. Meringue powder sidesteps that entirely because the pasteurization already happened before the powder reached the kitchen.

This is worth taking seriously and stating plainly rather than treating as an optional preference: raw egg carries a real risk that matters more for children, older adults, anyone pregnant, or anyone with a weakened immune system. Meringue powder whips up and dries the same way fresh egg white does, so switching to it costs nothing in the finished result and removes that risk entirely. Pasteurized liquid egg white, sold in cartons at most grocery stores, is the other common substitute and works the same way if meringue powder is not on hand.

Beyond the raw egg question above, royal icing itself is shelf stable once fully dried, since it is mostly sugar with very little water left in it. If you are baking or decorating for someone else, ask about allergies before you start, since egg and any added flavorings cross contact at the mixing bowl rather than only at the table. And if you are selling decorated cookies or cakes rather than giving them away, that is governed by your state's cottage food law, which varies a great deal from state to state and is worth reading properly once rather than assuming it matches a neighboring state's rules.