Chocolate mousse – stabilizing a foam

A good chocolate mousse is super smooth, airy, chocolatey and just melts in the mouth. It’s a great end to a dinner and is definitely one of my favorite desserts.

If you want to make it yourself though it can be quite finicky to say the least. How to prevent those clumps from forming?, why has it turned out so dense? or why has it collapsed? I definitely had some issues getting a chocolate mousse moussy. But, once you get the hang of it, you’re well rewarded!

A chocolate mousse really is one of those foods where some understanding of it will help you out. Once you understand what’s going on in all those different steps your chocolate mousse life will be easier. That doesn’t mean your next mousse turns out perfect, but you will understand what went wrong.

What is a chocolate mousse?

Sounds like a stupid question? But let’s get back to basics first before we dive into a recipe and how exactly you’d make a chocolate mousse. A chocolate mousse is a foam, air bubbles have been incorporated into a rich chocolatey mixture. The trick of any good foam is to stabilize the air bubbles into the foam. You do not want the air bubbles to disappear, or the chocolate mousse collapse.

When you make a meringue you stabilize the air by adding extra sugar and baking it. A cake is stabilized thanks to the flour that cooks in the oven. A chocolate mousse on the other hand is stabilized by cold and destabilized by heat.

The air bubbles in a chocolate mousse are surrounded by chocolate, possibly gelatin, cream and raw eggs. The raw eggs don’t really contribute in stabilizing the air bubbles, nor does the cream. Later on we will see that these two are more important to incorporate the air bubbles, than to stabilize them.

Chocolate & gelatin stabilize air bubbles.

It’s the chocolate and often gelatin that stabilize the air bubbles. Chocolate is solid at room temperature and even more solid in the fridge. This is because of the cocoa butter fats in the chocolate. Something solid is exactly what we need when stabilize a foam, the air bubbles will be stuck inside! Gelatin can form quite unique gel like textures. Gelatin is a protein mixture and these proteins can form a network which stabilizes all the remaining liquids in the mousse. Together, the gelatin and chocolate stabilize.

Can you make a chocolate mousse without gelatin?

Yes, you can as a recipe below will show you. Mousses without gelatin do tend to be a bit more delicate since it lacks one of the two stabilizers of your mousse. That said, you can’t just leave out the gelatin  of a recipe that uses it since it is made to work with gelatin.

Can you make a chocolate mousse without eggs, milk and gelatin?

Yes, you can. You can make a chocolate mousse of just water and chocolate. It works very well, but misses that lightness and airiness from the recipes described here. That said, for some applications, it works just fine! Since you’re leaving out the dairy and eggs, there’s a lot less of material to stabilize and that’s why you don’t need the gelatin anymore. The chocolate itself does all the stabilizing.

Making a chocolate mousse

When you make a chocolate mousse you will generally walk through the following few steps:

  1. Melt the chocolate
  2. Incorporate some fluid in the chocolate (e.g. egg yolks, some flavours)
  3. Fold in air by using whipped egg whites or cream

Each step has its own reason for taking it and its own risks for mistakes, so we’ll walk them through one by pan.

chocolate mousse cake
Chocolate mousse cake with a mousse in the middle strong enough to hold the top. You can also see the air bubbles!

Step 1: Melting the chocolate

If you don’t melt your chocolate, it will be impossible to add any air into it. So, of course, you have to melt it. Chocolate melts around 40-45°C so you don’t need very high temperatures. What’s more, depending on your chocolate type, it will burn if you hear it up too much. So melt chocolate gently.

The most conventional way to do so is using the au-bain-marie method (in a bowl above a pan with boiling water). I personally only use that method when I already have a pan on the fire for something else (if a sauce is bubbling away for instance!). In all other cases I use the microwave. The microwave method tends to be a lot faster than au-bain-marie.

How to melt the chocolate using a microwave

The waves can heat up the chocolate fat and melt it. Take care that a microwave has hot spots and cold spots though. This can result in part of your chocolate being very hot (and burning) whereas the rest is still solid. Therefore, only put the chocolate in the microwave for 30-60 seconds at a time and mix it in between. The more chocolate has melted, the shorter you should put it in at a time.

Step 2: Mixing in fluids

Chocolate and water aren’t compatible. If you’ve ever had a few drops of water fall in your melted chocolate you will notice it siezes up. This is very normal for chocolate to happen. By adding more moisture you can overcome the graininess again, making a ganache.

So what happens here. The chocolate you start with has a continuous fat phase. However, by mixing in moisture you are converting this to an oil-in-water emulsion. This means that instead of having oil with moisture particles in it, the ganache is water with oil particles in it. You just need enough moisture to form this continuous phase.

The more moisture you add after the more fluid it becomes. For a chocolate mousse you want it to remain quite firm or it won’t be strong enough to hold on to the air that you add in the next step. However, it shouldn’t be so firm that you cannot fold in any whisked cream or egg whites. This phase is often a cause for trouble when making mousses. Here’s few guidelines:

  • If you mix in a cold liquid with the chocolate it will cause the fat to set. This will make it very hard to create those small fat particles that float in the water. Try to have the liquid at room temperature. If it really becomes too hot you can melt it again slightly. Take care, because you only want it to heat a little (especially if you’re adding egg yolks here), but you can do so with the microwave, but gently.
  • If it stays very stiff at this point, too stiff to mix in anything else, just add a little more moisture to make a little softer.

Using egg yolks

A lot of recipes call for adding the egg yolks to the molten chocolate. Egg yolks contain quite a lot of fats and they will make your mousse even more creamy and rich. That said, the egg yolks aren’t cooked while making the mousse, they will remain raw. Keep this in mind and decide whether this is a risk you are willing to take (not advisable for young children, pregnant women or other groups at risk for food poisoning).

Step 3: Incorporating air

This is probably the most crucial step and it’s what will really define the consistency of your mousse: adding air bubbles into the mouse. The most common ways to incorporate is by whipping up a cream or egg whites and then folding these in.

Cream and egg whites are both very good in holding on to air and forming a light foam (see meringues & ice cream for more explanation on why they’re so good at it). However, they cannot hold on to the air for very long periods of time. With a chocolate mousse you use this capability to add air in these separate components. You then fold it into the rest of the mousse gently.

When you fold in these airy foams they main trick is to do it gently. You do not want to lose all the air when mixing it with the chocolate mass. This is why you are often asked to fold in just a part of the foam into the chocolate. This first bit will probably lose a lot of air. However, it will soften up and liquefy the mass a bit more. This will then make it easier to fold in the rest and you will lose less air in the process!

Chocolate mousse recipes

It’s now time to put your new understanding to work and make some chocolate mousse. There’s two recipes here, one based on Matt’s recipe from Masterchef Australia, the other one from Mary Berry’s baking bible.

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2 chocolate mousse recipe examples

  • Author: Science Chef
  • Cook Time: 30 mins
  • Total Time: 30 mins
  • Yield: 4 large bowls

Ingredients

Masterchef version – uses no cream for foaming & no gelatin

  • 170g chocolate (I used extra dark, but feel free to use milk or regular dark, I like my mousse bitter and not that sweet)
  • 80 ml milk
  • 2 egg yolks
  • 4 egg whites
  • 2 tbsp granulated sugar (regular sugar, I prefer to use a fine version which has slightly smaller crystals)

Mary Berry’s version, uses cream & egg whites

  • 175g chocolate (I used a 50/50 mix of dark and milk)
  • 1 tsp powdered gelatin
  • 2 eggs (split into egg whites and egg yolks)
  • 250ml cream

Instructions

Masterchef recipe

  1. Melt the chocolate in the microwave, stirring regularly (tips in the post).
  2. Mix the milk into the chocolate. You will see little threads forming at first but when you continue mixing it will become one nice goey mass.
  3. Cool it down to just a little above room temperature and whisk in the egg yolks (if the mix is hot at this point you egg yolk might set or curdle, which you definitely don’t want).
  4. Whisk the 4 egg whites with the sugar in a stand mixer or with an electric mixer until you have really nice firm peaks.
  5. Carefully pour about a third of the whipped egg whites into the bowl with the chocolate and gently fold it together (don’t use a whisk here, instead use a spatula, else you’ll break up all the air bubbles).
  6. Once all the egg whites are incorporated properly pour the mixture with the rest of the egg whites.
  7. Place in the fridge straight away (or eat immediately) and leave there until you’re planning to eat it (feel free to take it out a couple of minutes before eating to get to room temperature again).

Mary Berry recipe

  1. Mix the gelatin with 2 tsp of cold water to pre-soak.
  2. Melt the chocolate completely.
  3. Mix the egg yolks through the egg yolk. It will initially become very thick. If it firms up too much very gently re-heat it slightly, you don’t want to re-heat too much or the egg yolk will cook.
  4. Heat the gelatin mixture slightly so that the gelatin properly dissolves in the water.
  5. Mix the gelatin into the chocolate.
  6. Whip the cream until it’s nice and firm and holds it shape, don’t overwhip it, or it will become butter.
  7. Fold the cream through the mixture. You might want to only mix in half to start with before adding the rest.
  8. Whip up the egg whites until you have nice firm peaks again.
  9. Fold the egg whites through the rest of the mixture. Since you’ve already folded in cream it should be easier to fold in the egg whites.
  10. This mousse works great on cakes!

 

2 Comments

    • Hi Janel! Thanks for coming by. Once the mousse has set it becomes quite firm so I think it should well hold between two layers, although I never tried it myself. Don’t build the cake too high though (I would guess three thin cake layers with mousse should work) and make sure the mousse has properly chilled before building the cake. Chilling the mousse is super important to let the chocolate set and the mousse firm up.
      Good luck!

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