The science of meringue is easily explained, but no matter how many times I watch watery, viscous egg whites inflate into glossy white peaks, it always feels like alchemy. How could a simple egg white whipped with sugar transform into the voluminous lovechild of marshmallow and whipped cream? From mousses to buttercream to the toasted finish of a baked Alaska, it's one of the fundamental building blocks of pastry and a technique that provides fluffy, sweet aeration to hundreds of our favorite desserts.
Remarkably, the only ingredients needed to make meringue are egg whites and sugar, though an acid—usually lemon juice or cream of tartar—is often included as well. Here's how it works. Egg whites consist of water and proteins. As you whip the whites, you force egg proteins to unfold and bond around air bubbles, creating a new type of structure. As you continue to whip, the bubbles get broken down while the protein mesh gets stretched out thinner and thinner. Eventually, as the bubbles become so small that an individual bubble is not observable to the human eye, the whipped whites take on a glossy, shaving cream-like texture.
This basic concept remains the same for all meringues, but there's more than one way to skin a cat; the various methods to create meringue can be categorized into three different groups: French (made by simply whipping egg whites and sugar), Swiss (the whites and sugar are gently heated in a double boiler while cooking), and Italian (a hot sugar syrup is drizzled into egg whites as they whip). All three are useful in their own way, but today we're going to talk about Italian.
Italian meringue lends itself to a large range of uses. Whipping a hot (240°F!) sugar syrup into foamy egg whites doesn't just make it the most stable of the meringues—it's also safe to eat without additional baking, which is why it's traditionally used to make buttercream frosting, or "Italian Buttercream." Italian meringue is also the most involved of the meringues because it requires a little bit of sugar cookery, but once you understand some meringue basics and have a good thermometer, it's as easy as meringue pie.
Italian Meringue, Step By Step
Step 1: Combine sugar and water
In a heavy-bottomed saucepan, add your sugar. Pour in just enough water to give it the consistency of wet sand. For a four egg white meringue, you'll need about one cup of sugar and a half cup of water.
Step 2: Cook the syrup
Begin cooking the sugar on high heat, stirring only until it comes to a boil. Once it reaches a boil, stop stirring. Make sure to wipe down the sides of the pan with a wet pastry brush to clean off any sugar granules. This prevents small granules from caramelizing on the side of your pan and the sugars from crystallizing in mixture as it cools.
Step 3: Use a thermometer!
The moisture content and hardness of a sugar syrup can be accurately gauged by its temperature. In this case, we're looking for the "soft ball stage," the temperature at which a small amount of sugar dropped into a bowl of cold water will form a ball that holds together but is still malleable. Use a candy thermometer to monitor the temperature of your sugar. 240°F is what we're after.
Step 4: Start your meringue
While the sugar syrup heats, wipe the bowl of a stand mixer with a lemon wedge. (If you prefer, you can also add a 1/2 teapsoon of lemon juice or cream of tartar directly to your egg whites). Place four egg whites into the bowl and set your mixer to medium speed. You want the egg whites to reach soft peaks by the time the syrup has come to temperature.
To check for soft peaks, pull the mixer head out of the meringue. It should form gentle peaks that very slowly collapse back into themselves.
Step 5: Drizzle in your syrup
When your sugar reaches 240°F, carefully, carefully, remove it from the stove. (Hot sugar is just as dangerous as fryer oil, so use caution!) Very gradually stream the hot sugar syrup into your egg whites as they continue to whip on low to medium speed.
Step 6: Continue beating
Once you've added all of the syrup, increase the mixer speed to medium-high. Continue mixing until the meringue reaches the desired peak. Soft peaks are often used to aerate mousses, for example, while a stiff peak is best for buttercream.
Pro-tip: To clean out the pot you used to cook the sugar, fill it with water and bring it to a boil. This should dissolve any sugar that's hardened in the pan.
Making meringues is not hard, but here are some tips to make sure that you get the most out of those egg whites.
- Avoid fats: Since fat prevents egg white from foaming properly, its very important that your mixing bowl and tools are clean of fat or grease. Essentially, fats interfere with the bonding of the egg proteins as they whip, making it more difficult to create the foam structure.
- Use Eggs at Room Temperature: Room temperature egg whites whip up faster. The ideal temperature for whipping egg whites is about 70°F. Warmer egg whites make it easier for sugar to dissolve in the meringue. If all you've got is fridge-cold eggs, start by whipping them at a lower speed for a minute or two to help loosen and warm up the whites before switching to higher speed for volume.
- Don't Overbeat! If egg whites are whipped for too long they will eventually collapse because it has a curdling effect on the egg protein. To avoid over-whipping, keep you mixer at medium-high speed, rather than going full speed ahead. Once the sugar syrup has been added to an Italian meringue, it will become much more stable, and overbeating will be less of an issue, which gets us to...
- Sugar is your friend: The typical ratio for meringue is two parts sugar to one part egg white. Since eggs whites contain 90% water and only 10% protein, sugar helps create stability in foams because of sugar's hydroscopic qualities. In simpler terms, sugar binds with water and holds it in place. It also adds viscosity to the liquid whites, making the bubbles more stable.
- Add an acid: Adding an acid like lemon juice, cream of tarter, or even vinegar raises pH, helping to denature some of the egg protein. Whipping takes slightly longer, but the acid gives the foam more flexibility, making it less likely to collapse when you get to folding, piping, and baking—basically an acid is your stability insurance.
- Use fresh eggs for greater stability: It's often said that old whites are your best choice for making meringue, and in fact there is some level of truth to the claim. Old egg whites are thinner, so they foam more quickly and produce more volume, which was great back when people whipped meringue by hand. Thanks to the modern mixer, meringue making is a lot easier and older eggs aren't necessary. In fact, older eggs create a less stable foam because the liquid drains more easily from the bubbles. As a general rule of thumb, if stability is more important than volume, use fresher eggs.