filled macarons chocolate espresso

The Science of Macarons – Busted Myths and Tips for Success

Some recipes are super flexible. Add a little more butter or flour to these chocolate cookies, and they’ll still look and taste great. And a little more or less butter to your brownie and it will slightly change in texture, but still taste great.

Others, are more finicky and somehow can only be perfection or disaster, with no, just fine, in between. Macarons definitely belong to that second category. In every cookbook and in so many places online they’re discussed as being one of the more finicky cookies out there.

But what on earth makes them so finicky (aside from our perfectionist expectations that is)?

What are macarons?

Macarons are very delicate, exquisite cookies consisting of two layers of baked almond meringue with a creamy filling inside. The filling is pretty flexible, you can use chocolate ganache, fruit purees, various types of buttercreams and firm meringues.

The challenge for making these cookies perfectly, are the shells. The shells are very delicate. The outside is just crispy whereas the inside is slightly soft. A perfect cookie is pretty flat on top, allowing it to lie horizontally. That top is also smooth, curved like a dome on the sides. At the bottom of these sides the macaron have what they call ‘feet’, a bubbly layer of meringue.

It isn’t easy to get this ‘perfect’ shape. But you can get a perfectly fine tasting one, that just doesn’t look as perfect. As such, it’s a great challenge for those up for creating the perfect cookie. In all honesty, we’re not those people, we like a good looking, delicious, but not perfect macaron. But if you are, we have some great resources for you at the end. And for all of us, we have an explanation for how these cookies work, so that you have some good science to share, while eating your perfect/less than perfect macarons!

front view of single macaron shells
A flat(ish) smooth(ish) dome with feet at the bottom!

How to make macarons

At the end of this post you’ll find an extensive recipe, for now, we’ll focus on how to create those shells. The shells are actually a type of egg white meringue. You make them by whipping up egg whites with some sugar and then folding through a mixture of almond flour and icing sugar. To stabilize and crisp up these meringues, you bake them in the oven.

Whipping up egg whites

Whipping up egg whites for meringues isn’t as much work anymore as it was before the invention of electricity. An electric mixer makes this very doable energy wise, however, it is a task you can’t walk away from.

When you’re whipping up egg whites you’re slowly unravelling the proteins inside an egg whites. These proteins then sit around all those beautiful air bubbles you’re whisking in. There they stabilize the air bubbles. It’s why you can whisk up an egg white, but not a bowl of just plain water (foam science).

If you unravel (denature) these proteins too much though they become a bit stiff as a whole. As such, you don’t want to over whip your egg whites. Anytime you want to mix something through the egg whites you want the foam to still be a bit flexible and soft. If the foam is too stiff it won’t give way to your almond flour and icing sugar mixture and be very hard to mix through.

bunch of macaron shells

Mix egg white foam with icing sugar and almond flour

The next crucial step is mixing that almond flour and icing sugar through. You’re using almond flour for taste. However, almond flour contains a considerably amount of fat, which isn’t good for an egg white foam. The almond flour won’t actually dissolve into the foam. Instead, it will just sit in between all those air bubbles. It is why recipes ask you to use a very fine variety, or even grind it down further. The particles need to be small enough to sit in between all those air bubbles without creating clumps in the final batter. These clumps and pieces would show up as uneven bits in the shell.

You mix the almond flour with icing sugar and there’s a good reason for icing sugar. Icing sugar is nothing more than just very finely ground granulated sugar. You want these small particles because it helps the icing sugar to dissolve within your egg white meringue, again contributing to a smooth foam. If you use granulated sugar it likely won’t dissolve quick enough and you’ll be left with sugar crystals in the final meringue!

Piping the batter

In order to create evenly sized domes, you have to pip the batter onto a tray. you might think that piping would actually push out all of the air out of the batter. And whereas some will certainly be pushed out, this batter is through enough to hold. It’s similar to using a Swiss meringue for instance.

This meringue batter is actually quite special. It will be fluid enough to create a flat top. However, it won’t run down into a puddle. Really, all the previous steps are such to create this ideal flow behaviour (the batter even has a yield stress! this is (partially) what holds it into that dome shape). Since this flow behaviour has to be just right, just slightly different ratios of water to sugar or even the temperature can impact this. It is why, creating a ‘perfect’ meringue isn’t impossible, but requires some optimization for your situation.

Oven baking

While the meringues are in the oven, which is at quite a low temperature by the way, the outside of the meringue will start to dry out. This drying out gives it that crispiness. The outside dries out quite easily and form this smooth top.

However, while the meringue is in the oven, the center will start to heat up and as a result the air bubbles within the center expand. Often, the small air bubbles will coagulate and form one or a few larger holes. Simultaneously, water evaporates. This water cannot disappear through the smooth sealed top so it likely goes through the sides. It is one of our hypotheses for the formation of those feet at the bottom!

if this gas expansion or moisture evaporation happens too fast or too much, it might result in a broken/cracked top of the macaron.

Tips for a perfect macaron

There are various people online who have extensive guidelines for making a perfect macaron, though often with a disclaimer that every kitchen/ingredient choice might result in a slightly different result. We’ve grouped the better (more scientific) ones here for you!

Not so Humble Pie – Macaron 101

Ms. Humble has tried a lot of different macaron recipes and has written a mega long post on her journey. It’s a fascinating read for those interested. She even introduced a ‘scatter plot’ which I think is super cool of course.

She’s really tried a lot of different things and has come to a way of working that works well for her. That’s the kind of post I like, not repeating myths and tips others have mentioned, but actually checking whether they work for you!

One of my favorite parts is where she tested the difference between parchment paper and silicone mats. It’s not something you would commonly change but there’s quite a difference!

Food science guy

A great complete article style report in which the science of macarons is described. Two different types of sugar (regular granulated vs confectioners icing sugar) are compared when used in making macarons. Interesting article, although the literature study does seem to repeat several of the myths described above.

filled macarons chocolate espresso

Chocolate Espresso Macarons

Yield: 15-20 filled macaron
Prep Time: 30 minutes
Cook Time: 20 minutes
Additional Time: 1 hour
Total Time: 1 hour 50 minutes

This recipe will make great tasting macarons. If you're after a perfect macaron, be sure to follow the specific tips and tricks. If you don't mind a macaron with a little bit of a tip, and non perfect dome, you have a little more leeway.

You will need a piping bag. If you don't have one, you can use a regular Ziploc or freezer bag, just cut off a tip to pipe the batter.

Ingredients

Meringues

  • 60g almond flour (very fine, or seized and larger bits removed, see post for reasoning)
  • 100g icing sugar
  • 50g egg whites (from 2 eggs, take care there is no yolk in there at all)
  • 1/2 tsp lemon juice (optional)
  • 15g granulated sugar

Filling

  • 60g dark chocolate
  • 24g very strong espresso (or use 20g water + 4g instant coffee)
  • 36g heavy cream

Instructions

Meringue

  1. Sieve the almond flour and icing sugar together. If your almond flour is too rough to pass through a regular sieve, blend it for a few seconds in a food processor and try to pass it through again. Using flour or sugar with too large particles will make a less smooth macaron shell.
  2. In a stand mixer* add the egg whites (and lemon juice if using) and using a whisk attachment start mixing at a medium speed. After a minute or so it will start to become fluffy. Turn up the speed to high and continue mixing until it's a soft foam but not yet very stable. Add the granulated sugar (if you're making a double portion, add it in two parts, if not, you can add all at once since it's a pretty small quantity) and continue whisking until you have soft glossy white peaks.whipped egg whites for macaron
  3. Add about half of the almond meal/icing sugar mix and add it to the bowl with whipped egg whites. Gently fold the powder through the egg whites using a spatula. You want all clumps of dry powders to be gone. Don't mix more than necessary to prevent deflating the batter too much.
  4. Add the remainder of the almond/sugar mixture. It should now be easier to fold this through since you've already blended through the first half making the consistency easier to fold.
  5. Fill a piping bag with the batter. You can use a spoon to place spoonfuls on a baking tray, however, you'll be sure they won't look pretty (though will likely taste just fine).
  6. Pipe rounds of about 3-4cm in diameter (less than a centimeter in height) onto a baking tray covered with parchment paper (do not place directly on the tray, they will likely stick!). Your batter should be sturdy enough not to sink into a puddle.macaaron shells
  7. Leave the batter to rest while pre-heating the oven to 140C (285F).
  8. Bake in the oven for 18-22 minutes. The cookies/meringues should be dry on the outside and still have a little moistness within.
  9. Leave to cool slightly on the tray before removing them and cooling them further.

Filling

  1. Warm up the chocolate in the microwave (at high power, max. 20s at a time, keep a close eye on it, you don't want to burn it!).
  2. Once it starts getting soft, add your cream and coffee and continue to heat in short busts. Mix it through well in between heating cycles until you've got a consistent brown creamy filling. (Instead of using a microwave, you can also do this au-bain-marie, in a bowl on top of a pot of boiling water.)
  3. The filling will be very fluid just after you've made it, too fluid to place in between two meringues. Leave the filling to cool in the fridge for about an hour. Stir through regularly if you want to keep an eye on it. Once the filling can sit on top of your spoon without flowing off or sinking in, you can start filling the macarons.
  4. Using a spoon or another piping bag (although it doesn't have to be as neat, since you'll be pressing the two sides together) place a dollop of filling on the flat side of a meringue. Add enough to give about a 3-4 mm thick layer once the filling is spread over the whole surface. Take another meringue of similar size (if you're a pro in piping, yours will all be the same size, but admittedly, that's not my level) and gently push it on top. If your filling runs out, either press more gently or cool the filling for longer to firm more.

Notes

*This recipe has enough egg whites to be whipped up in a regular KitchenAid stand mixer. You can of course also use an electric mixer or your muscle power to whip up these egg whites.

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