Learn the science behind:
Choux pastry is a little piece of magic. A small, dense, little ball of dough, turns into a light and airy hollow ball in the oven! It serves as the perfect casing for a range of fillings to make profiteroles, éclairs, cream puffs, Bossche bollen (a Dutch specialty), and much more.
But, why does it work? And, what can make it fail? We’re going to dig into the science behind a good choux bun. By the end, you should understand just exactly why choux pastry is made the way it is. Giving you all the tools to make your own.
- What is choux pastry?
- How to make choux pastry
- Role of ingredients in choux pastry
- Troubleshooting Choux pastry
What is choux pastry?
Choux pastry is a special type of pastry. Raw, it’s a dense, slightly fatty, dough. However, once cooked and baked, it forms a slightly crunchy hollow shell, that’s very light and airy. Baked choux contains more air than dough. These large hollow spaces within are the perfect place for fillings, such as creme patisserie.
Choux pastry itself doesn’t have a lot of flavor. It is slightly eggy, but otherwise quite neutral in flavor. The role of choux pastry, therefore, isn’t necessarily to add flavor. Instead, its main role is to provide structure. To make a casing for a filling, and a surface to be decorated.
From small & round to large & long
You can find choux pastry in all shapes and sizes. Small round choux buns, to make profiteroles, or large ones to make Bosche bollen. Eclairs are made using a long, narrow version. You can use a lot of small buns to make a croquembouche, or just two to make a religieuse (French pastry).
Keep in mind, there is a limit to the size of your choux pastry. Make it too large and it will be too heavy. The delicate dough won’t be able to hold onto its own weight and might collapse. Or, the puff might not puff up enough due to all the weight pushing it down.
How to make choux pastry
To make choux pastry you first have to cook the pastry, before baking it in the oven. This two-step process is crucial for creating those large air pockets. Let’s have a closer look.
As an example, we’ll use the recipe at the bottom of this article. It’s a ‘traditional’ choux recipe, made with butter, flour, water, and eggs.
Step 1: Cooking the choux pastry
Making choux pastry starts by cooking a mix of flour, butter, and water into a thick dough. During this step, a few key processes happen.
During this step, you need to melt the butter (or a plant-based version). By melting the butter you can actually mix it in completely with the other ingredients.
Traditionally, you’d heat the butter with water (or milk) before you add the flour. However, we like to heat the flour & butter together, before adding the other liquids. It makes it a lot easier to stir in the flour. And, nice bonus, you don’t run the risk of your flour clumping.
Choux = Roux – Cooking the flour
Next, you’ll continue to heat your butter + flour mixture, until it has fully come together. At this point, we add our other liquids, just like you would when making a roux for a bechamel sauce, and continue heating.
This is a crucial step when making choux pastry. You need to continue to heat the mixture until it starts to thicken. We’re cooking the flour.
When cooking the flour, the starches gelatinize. That is, the starches absorb more and more moisture when heated, until, at some point, the pockets of starch burst. All the starch molecules are set free. Since these molecules prefer to bind to water, they’ll bind even more of it. As a result, the dough will thicken considerably.
Choux pastry isn’t unique for using this trick. When using water roux to make donuts, or making a hot water crust pastry, you use the same phenomenon. The starch becomes stronger and firmer, but also more flexible. It’s what enables the choux to rise and hold onto its shape so well in the oven.
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Step 1b: Cooling & Adding eggs
The choux pastry will be hot at this point. So, before you can proceed to the next step, you’ll need to cool down the pastry.
Right before baking the choux pastry, we need to add eggs. However, those eggs shouldn’t cook when added. They should remain raw. As such, you can only add them in, once the mix has cooled down. Eggs make sure your choux pastry turns more liquid again. It should now be easier to mix and pipe using a piping bag.
Step 2: Baking choux pastry
It’s time for the magic to happen! During baking, the thick, dense pastry will be transformed into a light and airy puff. To make it happen, space out your dollops of dough onto your baking surface. Keep in mind that they’ll take up more space once baked.
Want to spruce up your choux pastry? Add a thin layer of craquelin just before baking on top of the choux. This topping will add flavor and texture.
What happens during baking?
Once the choux pastry has entered the oven, various things will start to happen. First of, the dough will warm up. The butter melts, softening the dough. As a result, the dough becomes more flexible.
After some time, when the dough is hot enough, water within the choux starts to evaporate. The water turns into a gas. This gas will try to escape the choux pastry. However, it can’t because it is surrounded by a flexible, but impenetrable outer shell. So, instead, the gas just pushes onto the dough, causing it to puff up. This process takes some time. As long as the dough is flexible enough, it will continue to expand.
Remember that the flour has been gelatinized in the previous step. This helps in creating that very flexible expandable dough!
At some point though, the dough will start to set. The egg proteins especially will start to denature. This causes them to firm up, much like when cooking an egg.
Initially, the outside layer slowly firms up, whereas the inside is still soft. If you look closely at this point (see also the video above) you can see parts of the choux pastry pop out all of a sudden. This happens when the outer layer cracks. The inner layers of dough were still flexible, so they’ll expand to fill up the space, ensuring no holes are formed. This is when choux pastry gets its cabbage-like, uneven look!
The choux turns brown
Aside from these drastic shape changes, you’ll also notice that the color of the choux pastry will change. In the oven, it slowly turns a light brown color. This is because of the Maillard reaction. Sugar from the flour and proteins from the eggs and flour react together, to form brown molecules.
Role of ingredients in choux pastry
Making choux pastry is as much about controlling the steps we discussed above, as it is about controlling the ratio of its ingredients. You can make choux pastry with only 4 ingredients, but each of them has a clear and important role!
Water – flexibility
Water gives flexibility to the dough and ensures that you can even make a dough. You also need water to ensure the starches can cook and gelatinize.
Butter – richness & softness
Butter ensures that your final choux pastry is soft and rich. About 80% of butter is made up of fats. These fats give a pleasing sensation on your tongue.
But, butter does more!
While making choux, butter helps prevent the flour from clumping. If you’ve ever mixed hot water and flour, you know how challenging it can be to mix the too. As such as the flour hits that hot water it starts to gelatinize. As a result, the outside of a pocket of flour may cook, while the inside is still dry. If you’d break up one of these clumps, dry flour will fall out.
Mixing hot butter and flour doesn’t give this problem. The fats in the butter ‘protect’ the flour from the water. By surrounding the individual flour particles with fats first, they can’t clump together. The fats ensure they stay apart. Then, once the water is added, the water can access all of the flour, giving you a smooth mixture.
Flour – structure
Flour is crucial for adding structure to your choux and for ensuring it’s thick enough after cooking. It plays a key role in giving the choux the correct consistency. By absorbing water during cooking, flour also adds some flexibility to the dough, making it easier to expand, while at the same time being strong enough.
Eggs – key players
Without eggs, you’d have no choux pastry. The egg play a range of roles. First of all, eggs add more moisture and fats, just like water and butter. But, as we quickly alluded to before, eggs also add proteins. These proteins are sensitive to heat. Once they’re hot enough, they’ll denature and set. They give firmness to your final choux pastry.
Swapping ingredients in choux pastry
So you can make choux pastry with just there for ingredients. Getting the ratio of these ingredients right is crucial. Nevertheless, there are a few swaps you can make quite easily, without having a detrimental impact.
Butter vs. Margarine vs. Plant-based butter
Margarine is a plant-based version of butter. The exact composition and type will differ per country, but it’s a safe substitute to make. Do keep in mind that butter adds some flavor to the choux. Swapping it out for another fat will impact that.
Water vs. Milk
Our recipe just uses water as the liquid ingredients. However, you could also use (plant-based) milk. Keep in mind that milk tend to add some proteins and sugars. As a result, your choux will turn brown more quickly, make sure you don’t burn it. Also, don’t take it out too quickly, before the inside has cooked completely.
Troubleshooting Choux pastry
It is very important that the choux pastry can set fully in the oven. If you take it out too soon, it won’t yet be strong enough to hold onto itself. Instead, it will collapse! So, next time, bake the choux pastry for a little longer.
In the image below you can see what a mere 7 additional minutes in the oven can do. The choux bun on the right-hand side was taken out too soon. It collapsed. The other two don’t just have a nicer browner color, they are also firm enough to hold onto their shapes!