Foam icing is an old-fashioned cake topping. It is essentially a sweet meringue, made by heating egg whites in a double boiler with sugar, and whipping it until light and fluffy. The egg whites are heated to a food safe temperature of 160 degrees Fahrenheit in the process, which takes about seven minutes in a double boiler. This is why many older recipes call it "seven minute icing." Most recipes include lemon juice, cream of tartar or corn syrup to prevent the sugar from crystallizing and to make a lighter foam.
Things You'll Need
- 2 egg whites, room temperature
- 3/4 cup sugar
- 1/2 tsp lemon juice or cream of tartar
- 2 tbsp cold water (optional)
- 1 tsp vanilla extract, preferably pure
- Heatproof bowl
- Pot or saucepan
- Whisk or hand mixer
- Candy thermometer or instant-read thermometer
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Combine the recipe ingredients in a heatproof bowl, with lots of room for expansion. If you are using cream of tartar, whisk that into the water before adding the other ingredients.
Place the bowl over a pot of water that is simmering, but not boiling. Whisk the egg whites by hand or with an electric beater for five minutes, by which time it should have formed a light, glossy foam.
Test the temperature of the foam with a candy thermometer or instant-read thermometer. It must reach 160 degrees Fahrenheit for the egg whites to become pasteurized, and therefore food safe.
Remove the foam from the double boiler once that temperature has been reached, and add the vanilla extract. Continue to whip for another two to three minutes as it cools.
Once the foam has cooled, spread it lavishly over the cake, and between its layers if desired. Foam icing is usually applied in swirls and billows, rather than smoothed flat.