Fats in the Kitchen: Flakiness

We’ve seen that fats add tenderness to many of our baked goods, both by preventing tough structural molecules from forming and by contributing to leavening. But in bakes like pie crust, biscuits, croissants, scallion pancakes, and baklava, fat has another function: flakiness. In this post, we’re exploring how fats add flake to gain a better understanding of how to work with them.

Fats create layers.

We can summarize flakiness in one word: layers. Flakiness comes from thin layers of dough that are often crispy. It’s one of the defining textures of croissants, pie crusts, and baklava. Just look at the cross-section of a flaky pastry, and you’ll see what I mean.

These taro pastries (芋頭酥, yùtóusū) get their flakiness from thin layers of dough.

But if we simply stack sheets of dough on top of each other, they stick together, and we end up with a dense slab. No layers, no flakes. To create layers, we need something that will keep the dough separate. And that’s where fat starts to work its magic. Fat acts as a spacer that holds dough apart until it bakes into individual layers. Solid butter is perhaps most commonly used, but any type of fat, solid or liquid, will create layers because it repels water in the dough. Typically, the longer the fat remains solid, due to either its melting point or the size of the fat pieces, the flakier the pastry.

It’s helpful to group flaky bakes into three categories based on the type of fat and how it’s distributed throughout the dough. We can brush liquid fat onto sheets of dough, as in baklava or scallion pancakes. We can create alternating layers of solid fat and dough, called laminated dough, for croissants and puff pastry. Or we can scatter chunks of solid fat throughout dough, as in pie crust or biscuits. Let’s examine each of these groups in more detail.

Brushing liquid fat onto dough

Baklava and other pastries made with phyllo dough are flaky. Half of the secret is in the phyllo dough, which is rolled notoriously thin. The other half is less technical but equally important: fat. When we work with phyllo dough, we brush melted butter or oil onto each sheet before we stack the next one. It’s a tedious process, but the fat keeps each layer of dough separate so that it becomes one crisp layer. If we take a shortcut and brush only between, say, every five sheets of phyllo, the pastry loses some of its flakiness.

Liquid fats also create layers of dough in scallion pancakes (蔥油餅, cōngyóubǐng). We roll and stretch the dough into a rectangle, brush oil or melted animal fat on top, and then roll the dough and coil it into a pancake. The rolling creates layers of dough separated by fat. Crucially, the dough should be as thin as possible for the maximum number of crisp layers.

Liquid fat creates flaky layers in scallion pancakes (蔥油餅, cōngyóubǐng).

Type of fat

For these types of products, the fat is often chosen for its flavor. Melted butter adds richness to baklava, but olive oil might better complement the flavors in spanokopita. A neutral-flavored oil allows the aroma of the scallions to shine through a scallion pancake, but animal fat can add umami. No matter which fat we choose, as long as the amount is sufficient to coat the dough, it creates a flaky pastry.

Creating layers of solid fat

We can also alternate layers of dough with solid fat to create laminated dough. For the Western method, roll the dough into a rectangle and wrap a rectangle of butter inside. (You could also wrap the dough in the butter.) Then, roll the entire packet into a rectangle and fold it into thirds or quarters. Repeat several times. The number of layers increases exponentially with each fold. Cut the dough into individual portions, shape, and bake.

Laminated doughs are notoriously technical and time-consuming. To create even, unbroken layers, the butter and dough need to remain intact. The temperature of the butter is crucial for this. Too cold and it won’t roll as easily as the dough. The butter could split into chunks that tear the dough, or your rectangle could end up with unbuttered layers at the edges. But if the butter’s too warm, it melts. With repeated folds, melted butter simply gets worked into the dough and we lose our spacers, our layers, and our flakes. So between every one or two folds, we need to refrigerate the dough to ensure that the butter stays cold.

The characteristic honeycomb crumb of croissants starts with a laminated dough.

Type of fat

Margarines, especially puff pastry margarines made for laminating doughs, can alleviate some of these problems because they’re designed with a higher melting point. But they also have a waxy mouthfeel. And nothing compares to the taste of butter. Shortening also has a higher melting point than butter, but it’s 100% fat, whereas both butter and margarine contain water. Without water, shortening doesn’t create as dramatic a rise in puff pastry (more on this later!).

Lard, like shortening, is also 100% fat, but unmodified lard has an advantage over every other type of fat when it comes to laminated doughs. The solid fat in lard forms a different type of crystal. These crystals give lard its grainy texture, and their unique shape means they have a high melting point. (Unfortunately, these large crystals make both unmodified lard and melted, re-solidified shortening bad at holding air for cakes.) When a lard pastry goes into the oven, the large fat crystals stay solid for a longer time. By the time they finally melt, the surrounding dough has cooked so thoroughly it won’t sag, and the layers retain their integrity. So if the flavor of lard is complementary to the filling, a lard pastry might be worth a try!

Chinese puff pastry

Lard is also the traditional fat used for Chinese flaky pastry (酥皮, sūpí), though any fat can be used. Chinese flaky pastry envelops all sorts of fillings to make foods as diverse as curry puffs (咖哩角, gālǐjiǎo), egg tarts (蛋塔, dàntǎ), and yolk pastries (蛋黃酥, dànhuángsū). Chinese puff pastry uses two doughs: a water dough with water, flour, and a small amount of fat, and an oil dough with a high ratio of fat to flour. Home cooks portion the two doughs into individual servings, then wrap the oil dough in the water dough. They flatten the ball of dough into an oval, roll it into a tube, and repeat to create layers.

These mung bean pastries (綠豆凸, lǜdòutū) are made from flaky pastry.

Many people have an easier time working with Chinese flaky pastry than with Western laminated dough. One reason for this is the oil dough, which contains flour. The flour gives the fat a consistency similar to that of the water dough, which makes the two doughs easier to roll out together. Some Western laminated dough recipes also incorporate flour into the butter block to make it easier to roll, but not to the extent of an oil dough. Rolling the dough into a tube also creates many more layers than folding the dough into thirds or quarters, so the lamination process for Chinese flaky pastry goes faster.

Cutting fat into flour

The final method for incorporating fat into flaky pastries scatters chunks of solid fat throughout the dough. Recipes for pie crusts, biscuits, and “rough puff” pastry often include an instruction to “cut in the butter into the flour” with a pastry cutter, a food processor, or two knives or forks. The perfect mixture is often described as “coarse with pea-sized chunks of butter.” These chunks of butter are our fat spacers.

When we add liquid into the dry ingredients after this step, the butter forms pockets throughout the dough. The result? Two layers of dough, one above the butter, and the other below. Sometimes, this method is combined with the rolling and folding process of laminated doughs to create a few extra layers. Although cutting in the fat is much simpler than laminating dough, it comes with many of the same caveats. To keep the fat solid and cold, the liquid needs to be cold. We should use only our fingertips, which are cooler than our palms, to work the dough. And if possible, we should refrigerate the dough before baking it. You can watch these tips in action in this pie crust video!

Type of fat

Considerations for the type of fat we use are similar to those for laminated doughs. Lard can be a great alternative to butter. But for these bakes, we should note that, while fats add both flakiness and tenderness to our bakes, the two textures are contradictory. In order to create flakes, the fat must be chunky. But to add tenderness, the fat must be worked into tiny pieces that melt quickly in the heat of the oven to coat the flour. In an all-butter pie crust, we use the butter for flakiness and rely on other techniques, such as minimizing water and kneading, to reduce gluten. But using two types of fat, like shortening and butter, can create a more versatile crust. Because shortening is a little softer than butter, it coats the flour more thoroughly to add tenderness while the butter remains chunkier to create flakiness.

Putting the “puff” in puff pastry

As I alluded earlier, another important factor to consider in flaky pastry is leavening. How tall and how light will the dough grow? For puff pastry and biscuits, we want a dramatic rise. But for pie crust, we want to leave plenty of room for the filling.

Butter dramatically raises puff pastry because it contains 16–18% water. When the dough enters the oven, the dough layers begin to set. Ideally, it is only after this point that the butter melts. As it melts, a pocket forms in the dough, and the water within the butter becomes steam, pushing the dough upwards to raise it.

In raw dough (left), chunks of butter (yellow) are scattered throughout the dough. As the dough bakes (center), the dough sets and the butter melts, leaving pockets in the dough. As the dough continues to bake (right), water molecules (blue) from the butter vaporize and expand the pockets, raising the dough in the process.

Controlling puff

Of course, this only works if the dough is free to expand. If the dough layers are stuck together, the size of the pocket is limited. In hand pies, for example, the crimped edges don’t rise as high as the center because the dough layers are pressed together. In biscuits, if we twist the biscuit cutter in the dough, we risk gluing the dough layers together at the edge and limiting the rise of the biscuit. Or, if we’re slicing square biscuits, we trim the dough around the entire biscuit. Otherwise, the folded edges hold the dough layers together and the biscuit doesn’t rise as tall.

The crimped edges on these blueberry hand pies rise a little less than the centers.

Another way to manipulate the rise of flaky pastry is through the steam. For example, we can create more steam by adding liquid to the dough. Wet biscuit dough makes light biscuits because the extra liquid contributes to leavening. We also bake biscuits close together for greater volume. Since we trim the sides, we open some dough pockets, and steam at the edges can escape without leavening the dough. But by placing the biscuits close enough to touch as they expand, we keep more steam within the biscuits as they bake. In pie crust, though, we want to limit rise to leave room for the filling. So we poke holes in the bottom of the crust (a process called docking) to let steam escape.

Oven temperature is also crucial for a dramatic puff. The hotter the oven, the more quickly the water vaporizes, the more the pastry rises before the dough sets. If the oven isn’t warm enough, melted butter (and water) can leak out without leavening the dough, and the dough can become too firm by the time a significant amount of steam forms.

Type of fat

Since lard, shortening, and oil are all 100% oil, they do not contribute to leavening. However, margarine made for baking, which is essentially man-made butter, contains similar amounts of water, so it can also create puff. (Remember, though, that margarine tends to have a waxy mouthfeel and unrefined taste.)

Conclusions

Fats are instrumental to creating flaky pastries. In crispy scallion pancakes, buttery croissants, and fluffy biscuits, fat creates layers of dough that bake into delightfully flaky bites. And if the fat contains water, it creates steam that leavens our flaky pastry and gives it puff. But fat has even more functions in baking beyond adding tenderness and flakiness. In the next post, we’ll explore fats’ effect on textures in cookies and candies.



References

Corriher, S. O. Bakewise; Scribner: New York, 2008.

Figoni, P. How Baking Works, 3rd ed.; John Wiley & Sons, Inc.: Hoboken, 2011.

Hondoh, H.; Ueno, S. Polymorphism of edible fat crystals. Progress in Crystal Growth and Characterization of Materials, 62(2), 398-399, 2016.

Nelson, D. L.; Cox, M. M. Lehninger Principles of Biochemistry, 6th ed.; Freeman, W. H. & Company: New York, 2012.

SeaDragon. Huaiyang Flaky Pastry / Chinese Flaky Pastry 淮揚酥皮. Corner Café. 2008.

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