How exactly does a meringue get its airy texture? It all comes down to protein. All proteins contain sequences of amino acids that connect into distinct patterns to form coiled structures. When making a meringue, the egg white proteins must first be disassembled by breaking down their chemical bonds. This unfolds the proteins, but the amino acid sequences are still chained together.

This process is called denaturation.

Denaturation is a physical or chemical process. The egg white proteins that make up the meringue are physically beaten until they uncoil. Some recipes call for adding acid, which contributes to the chemical factor (1).

Fresh eggs are best for making a meringue because the proteins are stronger (can hold a more stable structure when put back together) and more acidic (helps break down bonds and slow the meringue process). Egg whites that are too old become more basic and harder to whip.

I’ve broken down the proteins. Now what?

As egg whites are beaten, air makes its way inside the liquid and creates bubbles, causing the structure to become a foam. On the layer between the air (from the environment) and on top of the egg white mixture, bonds form around the liquid that change it into a semi-solid state. This process is called coagulation.

If egg whites are over-whipped, the structure of the coagulated layer will break down, causing the air bubbles to pop. The amino acid chains will cross-link, and you will lose your airy creation (2). Bye bye, meringue!

This is where sugar comes into play.

Sugar is added to to the mixture just after the egg whites begin foaming. Sugar dissolves into the foam and bonds with the chains to lend water to the mixture. This aids coagulation, solidifies bonds, and increases protein elasticity. More air bubbles are present in the mixture, and the meringue becomes huge!

You may also incorporate a paste of water and cornstarch after mixing the egg whites with the sugar. This fortifies protein structure but slows coagulation (1).

Another factor to take into account while stabilizing the egg white foam is acidity. Acidity slows coagulation, so more air bubbles can form in the foam. Some meringues use vinegar, lemon juice, or cream of tartar to get this effect.

If you don’t have these ingredients- don’t panic! Silver or copper bowls will also do the trick. The silver and copper binds to available sulfhydral (sulfur with hydrogen) groups in the denatured chains, which delays coagulation (2). Now you can get voluminous meringues without the added cost of ingredients!

There are three stages of meringue. The “foamy” stage occurs when the egg whites are cloudy and yellow with large bubbles. The mixture is still in liquid form. The “soft peak” stage is seen when the egg whites become whiter, and lines from the whisk can be seen if you move your tool through the mixture.

Sugar is added during this stage (~1 tbsp at a time). When you remove your whisk after incorporating some sugar, you will see small peaks that won’t retain their shape for too long.

Finally, the “stiff peak” stage is completed when all the sugar is mixed with the egg whites. The meringue is beaten to full volume, and a thick, glossy texture is observed. The peaks will retain their shape after removing the whisk (3).

Time for some heat.

When meringues are heated or baked, the generated steam causes the air bubbles to expand, making more volume. Moderate heat will make the best meringue. Higher temperatures and/or increased cooking times will speed up the protein bond formations, and cause browning that prevents water from escaping. Low temperatures contribute to slow cooking, so the proteins at the bottom of the pan will not set. You’ll get a sad meringue, since it will “tear up” (leak water).

Quick fix- Meringue spread onto a warm pie or pan will start cooking from the bottom! You can also put fine cake crumbs on the surface of the pan or pie to dry out the meringue (1).

When done correctly, the meringue baking process will obtain a puffy, dainty, and delicious result. Let’s get cooking.

Sources:

1. “Demystifying Meringue.” Demystifying Meringue. GlenCoe Online, n.d. Web. 25 Jan. 2014. <http://highered.mcgraw-hill.com/sites/0078616441/student_view0/food_science_activities/demystifying_meringue.html&gt;.

2. Brady, John W. Introductory Food Chemistry. Ithaca: Comstock Associates, 2013. Print.

3. Jackson, Linda K., and Jennifer Evans. Gardner. Meringue. Layton, UT: Gibbs Smith, 2012. Print.