The science of meringue: egg whites & sugar

Made ice cream and have some egg whites left? Don’t feel like going through all the hassle of making marshmallows? That our go-to solution is to make some meringues. It would be a waste to throw the egg whites out and there always seem to be people around who can appreciate a well made meringue.

It’s so easy, just whip some egg whites, add some sugar, bake them or blow torch them, done.

Meringue is very light and airy, and somehow the egg whites are great at holding on to that air. If you’ve ever tried making meringue with milk or orange juice, you know it’s not going to work.

About time we take a closer look at meringues.

What’s a meringue?

Meringues are whipped egg whites with sugar, a sweet egg white foam is what it is. A lot of meringues have received some heat treatment as well, to stabilize them, but you can make a meringue without.

Meringues can be used by themselves, as a topping (on pie or eggnog), but can also be part of a dish. You use a meringue to add air to your chocolate mousse for instance.

You might have also run into French, Italian or Swiss meringue. Whereas the names aren’t always used consistently, these are all descriptors of a meringue that’s been heated. The main distinction is how the heat and sugar are added. The French version (in Dutch called schuimpjes) adds the sugar to the raw whipped egg whites and bakes them in the oven. The Italian meringue though uses a hot sugar syrup which is poured in with the beaten egg whites. Last but not least the so-called Swiss version gently heats the egg whites and sugars and only then whips them up.

Even though a meringue consists of only sugar & egg whites and maybe some heat, there are a lot of different meringues. Some are crispy, whereas other are soft, some can be piped whereas others are far too delicate to go through a piping bag. The opportunities are countless (just as they are for cookies!).

Why egg whites foam so well

A meringue starts with whipping up egg whites. A meringue requires a lot of air bubbles and a light foamy texture. Even if you whip an egg whites with a fork you will see air bubbles popping up. If you’d do this with water you might see some bubbles, but they will disappear again very fast. An egg white foam though can hold on to that air quite long.

What’s going on here?

Egg whites are mostly moisture and proteins, quite a lot (about 10%) of proteins but barely any fat. Egg white contains a mixture of proteins, the most prevalent one being ovalbumin. What’s special about this protein is that it can be denatured (unfolded) quite easily, simply by using some mechanical force (here’s where a whisk comes in play). When a protein denatures it unfolds. Parts of this unfolded protein chain like to sit in water whereas other parts do not (hydrophilic vs. hydrophobic). If at the same time air bubbles are incorporated into the egg white the parts that like to sit in water will sit in water, whereas the parts that do not will try to sit next to the air bubbles. This way the air bubbles are held in place by these unfolded protein chains.

The egg white proteins aren’t strong enough to hold on to the air forever. Over time, the air bubbles will coalesce and the egg white foam will collapse again. This is why a meringue has to be stabilized.

Meringues, ready to go into the oven
Meringues, ready to go into the oven

How sugar stabilizes an egg white foam

If you would try to bake your pure egg white foam, chances are that it will collapse in the oven. The heat of the oven evaporates the water in the foam. This makes it harder for the proteins to keep the air bubbles apart, essential all you’re left with is egg white protein. As a result, the air bubbles will escape and the foam will collapse.

This is why sugar is added to the egg white. Not only does the sugar sweeten the meringue, it has a very important structural role. Its first and foremost job is to help stabilize that egg white foam.

Adding sugar will increase the viscosity of the liquid phase in the egg white. Sugar dissolves in water, and if you dissolve enough it will form a sugar syrup. As you will have probably seen for your self, these sugar syrups tend to be a lot thicker than pure water.

By increasing the viscosity of the water phase, the sugar makes it harder for the air bubbles to merge together and escape. The air has to go through a layer of which the molecules don’t move as freely and don’t let the water through well. If you leave both a whisked egg white with and without sugar on your counter you will find that the sugary mixture stays foamy for a lot longer.

Powdered sugar vs granulated sugar

Depending on the type of meringue you’re making, you might be adding quite a lot of sugar to your meringue. In some recipes the concentration of sugar actually is close to the maximum amount of sugar that can dissolve in water at room temperature.

Since you want to dissolve all this sugar (else it will become gritty) recipes tend to call for using powdered (icing) sugar. The only difference between powdered and granulated sugar is the particle size. That of powdered sugar is a lot smaller and as a result it dissolves a lot more easily.

How egg yolk destabilizes an egg white foam

Before we dive even deeper into the world of meringues, let’s make clear that you really should only use the egg white and not the yolk for making a meringue. A yolk also contains proteins, but apart from that, it contains fat, which egg whites don’t. This fat can ruin your meringue.

As we discussed, proteins stabilize the egg white foam by unfolding and sitting on the surface between water and air. However, if fat is present, these proteins will not just sit on the water/air interface. Instead, it will probably prefer to sit on the fat/water interface, somewhat acting like an emulsifier. This severely limits the foam stabilization properties and as a result your foam won’t be as stable and will collapse a lot more easily.

whipping up Italian meringue

Firm, soft, light or dense meringues

By changing the ratio of sugar to egg white as well as by changing how and when you add the sugar, you can change the structure of your meringue.

There are of course a lot of moments you can add sugar to your egg whites, but there are two extremes: either at the start, before start to whip, or at the end, when you’ve already got your foam.

Generally speaking, adding the sugar at the beginning will give a denser structure. There tend to be more air bubbles, but they’re smaller. Also, it will take a lot longer for the egg white to actually form a foam when the sugar is already there. These types of meringues are sturdy enough to be piped in a piping bag and don’t need as much attention. If there’s plenty of sugar in there you aren’t that much at risk of overbeating the foam.

However, if you add the sugar add the end you’ve already created a very light egg white foam and the sugar will not affect the foam properties that much anymore. Instead, it will just dissolve and help support the egg white. You have to be more careful with this foam and most definitely cannot pipe it, you will push out all the air again.

A crispier French meringue

If you’re baking your meringue in the oven (French meringue style, you can find a recipe further down) the amount of sugar will impact the crunch and crisp of your meringue. More sugar will give a crispier sturdier meringue. This is because the sugar prevents the moisture from evaporating too quickly (so it won’t collapse that easily) but also because sugar itself, together with the protein, will form a sturdy structure that’s the actual meringue.

Once the meringue cools down the sugar will crystallize and the meringue will firm up. Sugar serves a very similar role in cookies, where it also contributes to crispiness.

A recipe for baked meringues (schuimpjes)

This recipe make small meringues that are baked in the oven to create a light crispy texture. It’s a good recipe to start with when developing a crispy meringue. Adding more sugar will make it even more crispy, whereas adding less will make it lighter, but you’ve just learned that, so should be able to figure it out.

Baked meringues / Schuimpjes
 
Prep time
Cook time
Total time
 
Author:
Ingredients
  • 2 egg whites
  • 100g sugar (standard)
  • sprinkle of salt
  • vanilla sugar
Instructions
  1. Whisk the egg whites (easiest is to use a stand mixer) until they've started to form a very soft foam. Add the used, salt and vanilla sugar and keep on whisking until the peaks in your peaks stay up by themselves.
  2. Bake at 100C for 45 minutes or until they're nice and firm. If you bake them too short they will collapse, baking too long will dry them out slightly.

A quick note on lemon juice & cream of tartar

Many recipes will call for using lemon juice or cream of tartar in your meringues. Both of these help stabilize your foam. In a lot of cases you can do without them but it will just give a slightly less stable or less firm foam.

Both work by lowering the pH-value of your egg white mixture. In other words, it makes the meringue mixture more acidic. These lower pH-values help the proteins to unfold and thus helps stabilizing your egg foam even better.

If you’re reading for leveling up your meringue science skills, it’s certainly worthwhile having a go with these two ingredients, but remember, you only need quite little amounts.

Further reading

Effect of sugar, citric acid and egg white type on the microstructural and mechanical properties of meringues, Fabio Licciardello, Pierangelo Frisullo, Janine Laverse, Giuseppe Muratore, Matteo Alessandro Del Nobile, 2011, Journal of food engineering, link

Effects of sucrose and sodium chloride on foaming properties of egg white proteins, Vassilios Raikos, Lydia Campbell, Stephen Euston, 2007, Food Research International, DOI: 10.1016/j.foodres.2006.10.008, link

A Study of the factors affecting the foaming properties of egg white – a review, K. Lomakina, K. Mikova, 2006, Czech J. Food Sci., 24: 110–118., link

Cook’s Illustrated on meringues, visited March-2018

Fine cooking on meringues, visited March-2018

On food and cooking, Harold McGee, 2004, p. 108-110

Exploratorium on egg foams

3 Comments

  1. Pingback: Paradise Meringues | RecipeReminiscing

  2. I LOVE your Blog Post on Meringues.

    Are you in Holland? Do you often post Dutch Recipes?

    I ask because I am looking for some Dutch Recipes
    and I am not having much luck finding a good Dutch Appelflappen.
    I have an old Dutch Cookbook, and use it for my Oliebollen, But, the Appelflappen
    is just making me a bit lost. 🙂

    I live in Sweden and all the Appelflappen Recipes I am finding call for self-rising flour,
    we don’t have this in Sweden.

    I have noticed that the difference between the Oliebollen, and the Appelflappen
    is that Oliebollen uses yeast, and it seems that Appelflappen uses baking powder.

    anyway, I look forward to reading more of your blog.

    • Hi!
      Thank you for reading my blogpost :-), I haven’t been writing a lot lately, but trying to write some more the coming time.

      Finding an English recipe for appelflappen might indeed be difficult, in my Dutch cookbooks I could find several :-).

      The easy way to make appelflappen is using store bought puff pastry (generally the frozen type). In the Netherlands you can buy this in squares of approx. 15-20 x 15-20 cm. Cut some apples in pieces and mix with sugar and cinnamon (to taste), place some apple mix in one half of the puff pastry and then fold the upper left corner onto the lower right corner to form a triangle. Fix both sides together with a fix and decorate with some egg to get a nice brown crust. Bake the puff pastry according to the instructions of the pack (generally 15-20 min at 200C. This is a method I generally use.

      In one of my recipe books I found a similar method, using either store bought puff pastry or ‘Hollandse korst’, which is a recipe for a Dutch puff pastry. It’s too complicated to completely explain here, but it consists of making a puff pastry dough from 500g flour + 3/4 tsp salt + 500g cold butter + 275 ml water. Cut the butter in cubes and gently mix with water and flour. Then follows a process of folding the dough, resting and cooling it, folding it again, etc. Just like with puff pastry. Once the dough is made they use half this amount for making 8 appelflappen. For eight appelflappen they mix 2 big apples (cut into pieces) + 35g sugar + 1 tsp cinnamon + 1,5 tbsp corn starch (Maizena in Dutch, which is just a little different from corn starch) + 35g raisins. This they use to fill the squares of dough and also coat with egg. It’s baked in the oven at 200C for 15-20 minutes. It’s pretty similar to what I do, feel free to vary quantities etc. to taste.

      Hope this helps :-).

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