food science: meringue

I geek out hard on the food science behind eggs, so it’s pure nerd joy for me to talk about meringue today. Meringue in general is an essential basic skill for any baker/pastry-er. As you may already know, I am a firm believer that having thorough knowledge of the how and why behind each recipe is the only real way to have complete dominance over your technique, so let’s look into the mysteries of meringue.

foam

We start at the very beginning. What is a meringue, not in the pastry sense but in the physical sense? In scientific jargon a meringue is simply a foam: gas dispersed in a liquid. Sounds sexy, I know. In the case of a meringue the gasses are bubbles of good ol’ O₂ (that’s air you numbskulls!) and the liquid is the water within egg whites. Somewhat uniquely is the addition of egg white protein, which we will talk about in much more detail shortly.

Basically, meringue is a ton of little air bubbles held together, so adding meringue to a recipe really means adding air more than anything else. In a mousse or buttercream a meringue will add volume and contribute to an overall light, fluffy texture. In a baked good like an angel food cake or biscuit (the French cake, pronounced “bis-quee” not the southern kind made by your meemaw) it’s bringing volume and texture to the party but it’s also going to help the product rise. Air is a powerful leavening agent!

Ok, meringue is a bunch of air bubbles and water, but what about the stuff that holds it all in? What about the protein??

egg whites

Obviously to know a meringue you must know egg whites (called albumen among the most scholarly) and luckily that’s not too hard to do. Egg whites are pretty much just protein (10%) and water (90%), with a few enzymes and a speck of glucose sugar thrown in for good measure. And as I mentioned, it’s the protein we’re most interested in.

Egg white protein is the literal and figurative glue that holds egg foams together. Without it, a meringue would never maintain its form long enough to be of any use in a recipe. At the basic level, air bubbles suspended in water is absolutely a foam, just not a stable one, because water within a foam quickly binds back together with itself to create, well, water (think of the head of a beer). It’s the protein in egg whites that becomes the structured network that gives the foam its stability.

There are six major proteins that make up the protein content of egg whites, but for our purposes we’ll focus on just a couple of them.

ovalbumin is the most prevalent protein in an egg white. It’s globular in structure, curling up into a sphere-like shape in its natural state. Parts of the ovalbumin protein chain are hygrophobic (repellent to water) and it’s that portion of the chain that is tucked away in the center of the sphere while the portion of the protein that is hygroscopic (attracted to water) surrounds it and interacts with the water in the egg white.

Ovalbumin uncurls or “denatures” (a protein in an unnatural form is known to be “denatured”) when heat is applied, so although there’s lot’s of ovalbumin in egg whites, it doesn’t do much to stabilize any meringue formed in a cold process. In a hot process meringue, like an Italian meringue or Swiss meringue, ovalbumin is a big part of the stabilization that occurs.

ovomucin makes up a little tiny part of egg whites – not even 2% of all the proteins present – but it makes up for a lack of presence with stabilizing power. Part of that power comes from its size (it’s the physically largest protein in egg whites) and also from its structure. While ovalbumin is spherical, ovomucin is fibrous, a sort of coiled rope. The size and shape makes ovomucin great at thickening egg whites and in turn plays a strong part in building stable meringue.

lysozyme is a crucial protein/enzyme because it plays a key role in protecting the egg white from harmful bacteria. Lysozyme creates chemical reactions that break down the cell walls of bacteria, basically annihilating them like a bacteria terminator. A Bacterminator, if you will.

Because of lysozyme (and other less studly enzymes) you can age your egg whites, which is a big deal. As you may have read in my post on macaron, aging your whites means allowing some of the water in them to evaporate, concentrating the protein content. It’s best to do this at room temperature, and while that would normally mean a bacteria growing bonanza, the Bacterminator keeps the egg whites safe*.

*If you age your whites and get sick, sorry not sorry, that’s on you! In no way am I guaranteeing that the enzymes in an egg white keep it 100% safe at room temperature. Wish I didn’t have to mention it at all, but this is America and half of you out there probably have a lawyer on speed dial. Just sayin.

salt

Salt is a common ingredient in a lot of meringue recipes, because in terms of flavor salt will both balance and enhance the finished product. But salt isn’t exactly a friend to meringue construction. When salt is added to egg whites it quickly dissolves into its base components of sodium and chlorine. The sodium and chlorine turns right around and bonds to the egg white proteins and that leaves less bonding sites for other egg white proteins to use to form long chains. Adding salt after your meringue has formed will ensure that all of the protein chains have safely bonded together and that any sodium or chlorine won’t be able to ruin the party.

acid

Acid is another common ingredient in a meringue, most often called for as cream of tartar (tartaric acid). Without getting too biochemistry on you, I’ll just say that while salt prevents protein chains from bonding, acid actually makes sure protein chains don’t over-bond. So remember: acid in the beginning of the recipe, salt at the end.

fat

Fat can safely be considered the arch-nemesis of meringue. If for some reason you have a meringue that doesn’t whip up or only whisks itself into a sort of foamy sludge, the likely culprit is a bowl or whisk that still has some fat from a past recipe on it or otherwise a bit of egg yolk may have snuck in with the whites.

Fat prevents meringue from forming in two ways. First, fat coats coiled up proteins preventing them from denaturing (uncoiling). Second, and most important, fat sticks itself in the neutral zone where air bubbles and water molecules meet. This is an important zone as we’ll see shortly, and when fat takes up space there, it keeps protein from getting in and bonding to hold things together.

Luckily, it’s pretty easy to prevent fat from ruining your meringue. Just keep your tools clean and be sure to carefully separate your eggs and all should be well. And no, if you do get fat into your meringue, there is no cure to save it. Cut the chord and open your heart to love a new meringue.

sugar

Of all the things you’ll add to your meringue, sugar is probably the most important. As always, sugar will make your meringue sweet, but it plays a big roll in the finished texture too. Here’s the basic guideline: The sooner you add sugar to your recipe, the denser and firmer the meringue will be. Again – sugar in the beginning = dense, firm meringue. Sugar at the end = light, fluid meringue.

When sugar hits egg whites early in the whisking process, it starts to dissolve into the abundant water, turning into a thick syrup. That syrup creates bulk and stability to the network of bubbles but also weighs the meringue down reducing overall volume. Heavy syrup doesn’t create light, thin bubble walls either, which is part of what makes the “sugar early” meringue so dense. Sugar molecules also get in the way of proteins trying to uncurl and lock together, so “sugar early” meringue will be slow to whip.

On the other hand, adding sugar late in the whisking process when the meringue is already formed will still create a thick syrup, but that syrup bulks up bubble walls that have already been built and so volume isn’t lost.

One thing to be careful of when you add sugar late in a meringue is giving the sugar crystals time to fully dissolve. Undissolved sugar will attract nearby water to it and form pools that will cause water seepage (what a terrible word) or will caramelize in unattractive beads on the surface of the meringue if you bake it.

the science step by step

step 1

The egg whites are whisked. I mean, no duh, but still, this is a very important first step! The tines of the whisk bring air into the egg whites. This of course begins to form air bubbles, but the opposing forces of air and water also pry the protein chains open, denaturing them. The tines pull water through the protein chains too, and that creates more uncurling.

Whisking too aggressively at this stage will incorporate too much air too quickly, before protein really has a chance to set up. This will ultimately build a meringue that’s weak and unable to hold itself up for long. Once a full foam has formed, without any clear albumen showing, it’s pretty safe to get serious about whipping.

step 2

More whipping. More air bubbles. More denatured protein. As the egg whites turn to foam, air bubbles and water molecules are isolated. Protein chains have opened enough to start to bind together, forming a matrix that will provide the stable walls for all ‘dem bubbles. As the protein network forms around the air and water bubbles, the hygrophobic portions of the protein face the air and the hygroscopic portions face the water.

step 3

Sugar is added, dissolving and creating a thickened syrup that further stabilizes the formed walls around the foam bubbles. The protein network continues to build and strengthen and the bubbles become smaller, creating a creamy texture in the meringue. At this point it’s a matter of managing the level of stiffness you need for your recipe.

step 4 – the point of no return

Uh oh! You walked away from your mixer to have a sip of cold, delicious, refreshing beer and got three deep before you remembered the meringue you had whipping. We’ve all been there. During your impromptu party, the protein chains continued to tighten until they bound so closely together that they squeezed air from the matrix decreasing the volume and squeezing water out too, forming pools of water at the bottom of the mixing bowl. What was once a creamy-smooth meringue is now crumbly in texture, more of a wad of protein than a fluid network of air, water and protein.

If you catch it soon enough, an over-whipped meringue can be mended with the addition of more sugar. The sugar will separate some of the tightly bound protein and also grab onto water before it exits to the bottom of the bowl. This of course sweetens the meringue beyond your original intent and still leaves the chance of undissolved sugar causing issues. Seriously over-whipped meringue isn’t really salvageable. On the bright side, that leaves you plenty of time for beer.

hot and cold

So far we’ve been talking about cold prep meringue, but what happens when heat is applied? I’m not getting into actual recipes and methods this week, but in broad strokes the two common hot process meringues are “Italian” and “Swiss”. Italian meringue uses a boiling sugar syrup that is poured over egg whites while whisking, and the Swiss variety is made by whisking egg whites and sugar over a hot water bath and then whipping them until they’re cool.

Each of the individual proteins in an egg white has a different level of sensitivity to heat, both in its ability to denature and its tendency to suffer damage. Yes, when introduced to prolonged heat egg whites (and eggs in general) will suffer some adverse effects in being able to create a foam, but those effects aren’t really noticeable in our realm and the benefits still outweigh any of that negativity.

With heat, ovalbumin – that most prevalent protein in all the egg white land – will finally denature and that adds a lot of stability. Sugar also dissolves more efficiently into warm water, so the sugar syrup created in a hot process meringue is stronger too.

In a Swiss meringue, the mixture is heated so much that the egg whites actually pasteurize, so the finished product is stable at room temp.

While we’re on the subject of pasteurization, what about using pasteurized egg whites? Well, what about it? Go for it! Commercially pasteurized egg whites are treated with minimal protein damage and will behave a lot like the fresh counterpart. Maybe it’s in my head, but I feel fresh egg whites make a better meringue. That doesn’t mean I won’t use pasteurized whites. They’re cheaper for one thing, and they make a meringue that’s stable at room temperature.

conclusions

Well hot damn, that’s a lot of egg info! Lots of sciency papers I read have a section at the end entitled “conclusions.” I figured to look super smart I should have one too. I hope this gives you a good idea about what’s going on in your mixing bowl while you’re making your next meringue. If you’ve been avidly following the blog – and who in there right mind wouldn’t!? – your head has probably increased in size because of all the extra food smarts we’ve packed in there. Better get some new hats.

Oh and not to worry, I’ll deliver some actual meringue recipes to you before too long. So stay glued to your computer and/or mobile device until that day arrives!

Cheers – Chef Scott

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