Have some egg whites left from that ice cream or custard recipe you made? Don’t feel like going through all the hassle of making marshmallows? You will then probably end up using it for an egg white omelet, or, meringues! You can use meringues to top off a dessert, or you could just eat them as is. You can make them in all sorts and sizes, crispy or soft and smooth. The basic concept is simple: whip some egg whites and add some sugar.
Meringues are essentially egg white foams. The egg whites are great in holding onto air bubbles and forming a foam, whereas the sugar is there to stabilize it all so it doesn’t collapse again too quickly. There’s some great science involved that will definitely help you make even better and more varied 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 heat.
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. The meringue serves to incorporate some of those desired air bubbles into your mousse.
Types of meringue – French, Italian, Swiss
There are a lot of different types of meringues. A common classification is to group them 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.
For the French version (in Dutch called schuimpjes) you add sugar to raw whipped egg whites. This mixture isn’t stable over time, so you bake them in the oven (see recipe at the end of this post). This makes them crispy, but still slightly soft on the inside. By heating them and drying them out slowly you can store these for a long period of time as long as you store them in an air tight container.
When making an Italian meringue you first make a hot sugar syrup. You then pour this hot sugar syrup over and through beaten egg whites. The heat of the syrup cooks the egg whites, stabilizing them.
Last but not least, in the so-called Swiss version you gently heat up the egg whites and sugar together while whipping it. Once they’ve reached the temperature you’re aiming for you increase whipping drastically. This meringue definitely isn’t crispy, but it is very light and airy and even stable enough to pass through a piping bag without losing all the air again.
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.
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.
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.
- 2 egg whites
- 100g sugar (standard)
- sprinkle of salt
- vanilla sugar
- 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.
- 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.
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