Citric Acid and The Science of Meringue

Of Eggs and Sugar

Meringue, one of the simplest preparations in a kitchen [simple being relative; read on], is the combination of egg white and sugar. Funnily enough, acid has an interesting effect on both ingredients. In egg whites, acid helps loosen the proteins and keeps it loose for longer so more air can be whipped into it. In sugar, acid interferes with crystallization, so melted sugar stays melted while it’s cooking. In other words, acid is instrumental in producing lighter, stiffer egg whites and sugar that won’t recrystallize.

Sounds like the makings of a perfect meringue.

Hot, Hot, Sticky, Sweet

Sugar when heated, has this annoying tendency to want to convert back to a crystalline structure as it cools. To prevent this, ingredients are added to interfere with this process. Recipes commonly call for a squeeze of lemon juice when heating sugar to keep it from recrystallizing. Some might include a touch of corn syrup (which has a pH of ~5). For the purpose of keeping sugar melted, a couple of pinches of citric acid will also do the trick.

It bears repeating that you cannot work effectively with heated sugar without a thermometer of some kind. Whether it’s an infrared gun or a traditional candy thermometer, it is essential that you are able to measure the temperature of cooking sugar with accuracy. You can’t simply “wing it.” The properties of sugar can vary greatly within 25 degrees, and are virtually indistinguishable from one another visually, with the exception of caramel. And by that time it’s probably too late [unless you’re making caramel, of course]. The chart that show the stages of candy temperatures is interesting, but no one needs to know it; the recipe is going to tell you precisely how hot to make the sugar.

I should also mention that sugar gets hotter than boiling water, so avoid at all costs coming into contact with cooking sugar until it’s cool enough to touch. Again, a thermometer makes a difference.

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4 thoughts on “Citric Acid and The Science of Meringue”

  1. Brilliant, thank you! I love marshmallow frosting but it's very tricky to work with and doesn't usually come out the way I want it. I'll try using swiss meringue. Can I use a hand mixer instead of a mixer? Can I add vanilla extract or use vanilla sugar?

    1. In general yes, you can use a hand mixer for batters and foams. Swiss meringue is the basis for 7-minute frosting.

      Vanilla sugar is usually synthetic, and tastes as such. You *can* make your own by burying a vanilla bean in sugar for a few weeks, but stick with real, pure vanilla extract for the best flavor.

  2. Yes – I tried being cute and making "Lemonade Meringues" using lemonade mix. Due to high acid, they came out more like mentos. I guessed a base, like baking soda, might counter. They'll make gas, also.
    But just 3 eggs to 2 1/4 cups sugar works w/o the tartar or other leavening.

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