Royal icing is the decorator’s cement, a smooth paste of powdered sugar and egg white that dries hard and holds its shape. The same bowl of icing can outline a cookie, flood a smooth background, or pipe a stiff flower, and the only difference is how much water it contains. This calculator works out the egg white and water for the consistency you need.
Stiff royal icing uses the least liquid, with egg white at about sixteen percent of the sugar weight and no extra water. It holds sharp peaks and keeps piped flowers, leaves and lettering exactly where you put them. If stiff icing slumps or loses detail, it has too much water, so add powdered sugar a spoonful at a time until it holds a peak.
Outline icing adds a little water to reach twenty percent total liquid, which makes it flow just enough to pipe a clean border. The border acts as a dam that holds the flood icing inside, so it must be firm enough to stand up but smooth enough to pipe without breaking. A good outline dries to the touch in about twenty minutes.
Flood icing is the thinnest consistency, at about twenty six percent total liquid, and it flows smoothly to fill the space inside an outline. It should settle flat within about fifteen seconds after piping, which decorators call the fifteen second rule. If it settles faster, it is too thin and may overflow the border or dry with craters.
Egg whites give royal icing its strength and shine, and one white weighs about 30 grams. For 500 grams of sugar, stiff icing needs about 80 grams of white, which is roughly three whites. Weighing whites keeps the ratio exact, because whites vary in size and a count only recipe can drift badly between batches.
Water must be added a teaspoon at a time, because the jump from outline to flood is small and easy to overshoot. Stir gently rather than whisking hard, since beating in air creates bubbles that dry as pinholes in the finished surface. If bubbles appear, let the icing rest and stir slowly to release them before piping.
Meringue powder is a safe alternative to raw egg whites, and it suits anyone who wants to avoid raw egg. Use about one tablespoon of meringue powder per 100 grams of sugar, plus water to reach the same total liquid as the calculator shows. The dried result is just as hard and glossy, though the flavour is slightly different.
Colour royal icing with gel food colour, not liquid colour, because liquid colour adds water and changes the consistency you just measured. Add colour before the final water adjustment, so you can correct the thickness after the colour goes in. Dark colours need time to deepen, so mix them an hour ahead when you can.
Drying time depends on thickness and humidity. Thin flood icing dries to the touch in a few hours but needs overnight to harden fully, while stiff details dry faster because they hold less water. Do not stack or bag decorated cookies until the icing is completely hard, or the surface will dent and stick.
Store leftover royal icing in an airtight container with plastic wrap pressed onto the surface, and it will keep for up to two weeks in the fridge. Stir it gently before reuse and check the consistency, because it often thickens as it sits. A few drops of water bring it back, added slowly and stirred well.
A worked example helps with small batches. For 250 grams of sugar, stiff icing needs about 40 grams of egg white and no extra water, while flood icing needs the same 40 grams of white plus 25 millilitres of water. Small batches are easier to control, so mix a fresh bowl for each colour rather than tinting one huge batch.
Flooding is a calm, step by step process. Pipe the outline first and let it crust for ten minutes, then flood the middle with a piping bag or squeeze bottle and guide the icing into the corners with a toothpick. Work on one cookie at a time and pop any bubbles with the toothpick before the icing starts to set.
Calculadora de Consistencia de Glasa Real – Glasa Fluida, de Borde y Firme