lemon meringue tart cut in two

Swiss meringue – Science of a stable, delicious pie topping

It is super easy to whip up egg whites and create a light and foamy consistency. The tricky bit though, is to ensure that the air stays inside and doesn’t deflate out again! This is a common challenge, whenever you add air into your food, whether it’s whipped cream, a meringue or a mousse.

It becomes even more challenging when you want to make a topping for a pie or cake that you deposit using a piping bag. During piping you press considerably on the foam, risking getting rid of all of that air again! So you need to stabilize the foam enough for it to handle all this force. A Swiss meringue, one of many types of meringue, does just that.

Holding on to air

There are several strategies to keep air in your food. For one, you can add an ingredient that solidifies and stabilizes the foam. This is what the chocolate in a chocolate mousse does. Another alternative is to dry out the foam, which makes it solid. This is what you do when making a French meringue. Another option is to handle the foam very carefully, but this is not really an option when you want to pipe the foam on top of your pie.

A Swiss meringue uses other strategies to stabilize the air.

How Swiss meringue works

The thing that sets a Swiss meringue apart from other meringues is how you heat it. A Swiss meringue is made from just sugar and egg whites, no additional water. You whip the egg whites and sugar and then heat it up above the pan of boiling water until it is at least 71C. It’s this heat that sets Swiss meringue apart from the rest.

It starts with the egg whites

Like any meringue, Swiss meringue gets its airiness from the whipped up egg whites. The proteins in egg whites are very good in holding onto air once they’ve been whipped up. The proteins unfold because of the whisking and position themselves around the air bubbles to keep them in place.

When you whip the egg whites you create air pockets which are surrounded by the egg white liquid, which is mostly water. By adding sugar to the meringue, you increase the viscosity (aka make it thicker) of that water in between the air bubbles. This prevents the air from escaping from the meringue too quickly.

Then the heat kicks in

By heating up the egg whites & sugar you accomplish a few things. First of all, the increased heat helps to dissolve all that sugar in the egg whites. At a higher temperature, more sugar dissolves in water, which makes a super smooth meringue, you don’t want any crunchy sugar left.

The heat does more though, it helps the egg white proteins unfold. As a result, it can stabilize the foam better. The heat doesn’t fully denature the egg whites, it’s not hot enough for that, but definitely helps it to stabilize the foam as a whole.

Making a buttercream version

Whereas you can use Swiss meringue as is, you can also use it to make Swiss meringue buttercream. Over time Swiss meringue might soften and collapse slightly. Adding butter enriches the Swiss meringue and firms it up, preventing it from collapsing!

lemon meringue tarts
Swiss meringue is stable

Because of the combination of egg whites + sugar + gentle heat you create a very stable foam. The air bubbles in this foam aren’t very large, but they are very stable. As a result, a Swiss meringue can handle quite a bit. You can pipe it through a piping bag. It has gained enough strength to withstand the forces you exert on it while piping. It sometimes even looks a bit like a marshmallow (but more sticky and soft), which can also be piped before it’s dried.

Comparing meringues

There are a lot of different types of meringues. The Swiss meringue is most suitable for piping and dosing onto a pie or other baked good. The French meringue on the other hand is crispy crunchy, better suited for a Pavlova.

The Italian meringue is very similar to a Swiss meringue, however, instead of gently heating the egg whites and sugar together, you actually create a separate hot sugar syrup. You then pour the sugar syrup with the whipped egg whites. This adds even more heat and stability to the meringue and creates a slightly different texture, although, this one is probably most similar to the Swiss version.

It’s the heat treatment that sets them apart and creates those very different challenges!

Browning Swiss meringue

Swiss meringue is perfect to top a pie and you can make it even more spectacular by blow torching the top. The reason they brown so beautifully is the large amount of sugars & proteins. These two are necessary for the Maillard reaction (a browning reaction) to occur. The heat will induce Maillard reactions in the meringue which results in a brownish colour.

lemon meringue tart cut in two

Swiss meringue

Yield: enough for 6 small pie toppings
Cook Time: 20 minutes
Total Time: 20 minutes


  • 2 egg whites (= approx. 55g)
  • 110g sugar*


  1. Get a stand mixer ready with the whipping attachment.
  2. Bring a pot of water to the boil.
  3. Take a metal bowl and whisk the egg whites and sugar together loosely.
  4. Place the bowl on the pot with boiling water and, while whisking continuously, but not very vigorously. You just want to make sure it heats evenly. Track the temperature of the sugar and egg white mixture.
  5. Once the mixture has reached 71-75C, take it off the heat and pour it into the bowl of the stand mixer. Whip it up immediately at a high speed until is is very light and fluffy. It should turn a beautiful white colour.
  6. Continue whisking until it has cooled down to room temperature (stop whisking sooner if you see it collapsing again).
  7. When the meringue has cooled down to room temperature you can fill a piping bag with the mixture. This has several advantages, the piping bag prevents the meringue from drying out any further and keeps it nice and soft besides making it easier to decorate something with the meringue without getting sticky fingers.
  8. Using a blow torch** brown the meringue on the top, be careful not to burn it!


* Use twice the weight of the egg whites, if your egg whites are lighter or heavier, adjust the sugar recipe; also, for larger portions, use more egg whites and simply multiply their weight by two to determine the egg white content.

**If you don't have a blow torch you can also use the grill function of your oven. Put it at quite a high heat, you want it to brown as quick as possible without heating up the rest of the pie/tart that's below it. It depends on the quality of your grill whether you can make it a nice brown.

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