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So many cuisines have dishes that are made with super thin pastry. The very thin dough can be used for making anything from Middle Eastern baklava, Greek spanokopita, German strudel to Indian samosas. They’re all made with phyllo, or the very closely related strudel dough.
The layers in these pastries are so thin that you might well be wondering how they manage to make them. Once they’re baked, you can still see these separate layers and they have probably turned deliciously crispy.
If you’ve ever tried to make this dough with anything other than wheat flour, you will have found that this is just about impossible to do with anything else than wheat flour. Pulse, nut, rice or coconut flours will all turn out slightly different (although some online recipes do come really close!). The main reason for this? The (lack of) gluten!
A good reason to dig a little deeper into the science of one of these super thin dough dishes: apple strudel.
What are phyllo & strudel pastry?
Phyllo and strudel pastry are both very very thin doughs, so thin that they’re almost translucent. Several layers are stacked on top of each other, after being coated in a thin layer of fat to make a sturdy enough crust. Both pastry are made from mostly wheat flour, water and maybe some salt. Some recipes, especially those for strudel, contain a little fat and or egg (the recipe at the bottom of this page does). A crucial step in making the pastry is to leave the pastry to rest (more on that later) after which it is rolled out or pulled into that thin sheet of dough.
The fact that these layers are so thin makes phyllo and strudel pastry different from other pastry types such as puff pastry. In puff pastry or a croissant dough the dough is folded around the fat and finally rolled out as one sheet. The layers of pastry really only become visible once you start baking, when the fat melts away. Phyllo & strudel doughs though have these individual layers from the get go.
Science of making thin dough layers
Whenever you want to make very thin layers of food, you will run into challenges. A very thin material is very fragile, easily loses its moisture and is generally a lot easier to make thicker than thinner.
Apart from phyllo or strudel dough there are only a few foods with these thin layers and most of them use heat to help them build structure. Brick pastry and spring roll wrappers for instance are made by spreading a very thin layer of batter on a hot surface and heating/steaming it just enough for the batter to get firm enough (thanks to the starch cooking). Crepes are another good example, although they already tend to be a little thicker! Indian papadums remain unheated until the final cooking and are thin as well, but again, not as thin as phyllo.
The power of gluten
Strudel and phyllo dough though both don’t get any heat until the final baking process. So what allows these doughs to become so thin and still possible to handle? We shortly alluded to it in the introduction already, the reason it works is the gluten.
Activating the gluten
Making these two doughs requires making quite a stiff dough of white plain wheat flour and water. It is essential you knead this dough well and make it softer and more pliable. What is happening here is that the gluten, which are proteins in the wheat flour, are activated. That is, these proteins start aligning and organizing themselves. This is a pretty spontaneous process (it’s why you can make no-knead bread, you do need patience!), but kneading help speed it up and bring everything together. It can’t happen in the flour on forehand since there needs to be enough water for the proteins to move freely and orient themselves. Dry flour doesn’t give them this ability.
When you’re baking bread you’re also looking for this gluten development to occur. However, in that case it is to help hold onto air bubbles that form within the dough. In other applications, such as scones, you don’t want any gluten to form!
Window pane test
If you’ve baked bread before, you might have heard of the window pane test. This test is actually a great way of showing what happens when you’re making your dough.
As part of this simple test you take a piece of dough, about 10-20g. With your fingers you then gently try to stretch the dough ball into as thin a layer as you can. If you haven’t kneaded you dough yet you will notice that this is almost impossible. As soon as you stretch the dough it will break, it won’t stretch.
However, if you continue to knead you will notice this becomes easier and easier. A guideline for bakers is that a dough is kneaded enough if you can stretch the dough into a thin enough layer that you can see your fingers through. Remember how we said we want to get our phyllo & strudel dough that thin? We definitely need a dough that’s structured enough to hold onto this thin sheet!
Relaxing the gluten
When you’re kneading a wheat flour dough you’re stretching and stretching all those proteins and ensuring they align. It’s what develops the dough, but it does put a lot of tension on the dough. Ideally, part of that gluten wants to relax again slightly.
If you’ve ever tried rolling out chapati or pasta dough immediately after you’ve kneaded it, you may have noticed it can be quite challenging. It will continue to pull back after you’ve rolled it out. However, if you leave it to rest, the dough is a lot softer and easier to roll out.
When you’re making strudel and phyllo dough you will have to roll out your dough from a small ball into a sheet that’s easily 20 times its surface area. In other words, you have to make sure that gluten is truly relaxed and not wanting to curl back up again all the time.
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Creating the mighty thin layer of dough
So after kneading that dough and leaving it to rest (you can easily leave it overnight) the dough should be ready for stretching. All you have to do now is, carefully, roll out the dough into thinner and thinner layers (you might need quite a big rolling pin for this!) or gently pull on the dough, stretching it section by section.
The dough itself is quite a firm dough which is essential for the stretching. If it would be too wet at this stage, it won’t stretch out evenly.
Protecting the dough layers
Remember that these doughs are very thin. As such, they dry out very quickly. Phyllo & strudel doughs therefore aren’t doughs you’d make too far in advance (unless you plan on freezing them). Also, to keep the doughs pliable you will generally be asked to brush these thin layer with some sort of fat. This keeps the separate layers when it’s baking in the oven (the fat prevents the layers from the starches in the layers from sticking together), but it also forms a barrier against moisture. This way it doesn’t dry out as easily and stays more pliable.
Why you buy phyllo dough frozen
Because phyllo dough dries out easily, but also sticks to other layers easily, you will generally only be able to buy it frozen (or ultra fresh). Freezing the dough will prevent the different layers from sticking together as easily since the water transforms into ice. Also, if wrapped properly, it prevents excessive loss of moisture (although you can get freezer burn).
The disadvantage of frozen phyllo dough is that it makes it super fragile. Because all the water freezes and turns solid, it loses some of its flexibility. This is why it’s so important to fully defrost the dough before using it! It will make the dough flexible and easier to use again.