Fats in the Kitchen: Spread and Consistency

Over the last few posts, we explored how fats create tenderness and flakiness in our bakes. These functions mainly result from fats’ tendency to repel water, but other applications of fats come from their greasiness. By lubricating the ingredients in our mixing bowls, fats can affect bread rise, cookie spread, and fudge texture. They’re also essential for making sure our bakes come out of the pan. In this post, we’ll focus on the roles of fats that stem from their greasiness.

Fats are slippery.

Before we explore fats in baked goods, let’s first consider why fats are slippery. Because of how their atoms are arranged, fat molecules don’t stick much. They’re like blocks of wood, whereas water molecules attract each other like magnets. If we have two magnets stuck together, it takes some effort to slide one against the other, so water isn’t nearly as greasy as fat. But if we have two wooden blocks? Not a problem. Because fat molecules aren’t attracted to their neighbors, they’re easier to move, so they feel greasy.

Fat molecules (left) don’t really attract each other, but water molecules (right) do. The attractive forces between the water molecules are represented by black lines.

When we add a layer of fat to our baking pans or our ingredients, we make them slippery. We know greased flour forms less gluten and creates more tender bakes. But when fats lubricate other ingredients in bread, cookies, and candies, its effects extend beyond tenderness.

Fats can increase bread volume.

As we mentioned in the post about tenderness, fats can lubricate gluten proteins and increase the stretchiness of bread dough. This helps the dough trap more air and rise to a greater volume in the oven. Many recipes add fat by kneading softened butter into the dough or by letting the dough rise in a greased bowl.

Remember that we can think of gluten as Slinky coils. When bread rises, the Slinky coils stretch to accommodate the extra volume. Without fat, the coils occasionally interlock, which limits how far they can stretch. But with fat, the coils slide past one another more easily. We can see this stretchiness in the structure of the dough itself. Doughs with more fat stretch paper-thin before they break.

This milk bread dough contains plenty of butter, so it can stretch very thin.

Notice that, for fat to increase the stretchiness of a dough, there must already be gluten in the dough when we add the fat. Therefore, we must add the fat after the gluten develops and the dough forms. In recipes where the fat is added with the other ingredients (like oil that’s added to the flour with water or milk), the fat coats more flour particles and less gluten strands. The resulting dough is more tender.

Fats increase cookie spread.

The greasiness of fats also plays a role in the shape of cookies. Fats lubricate the solid flour particles in cookie dough and help them slide past one another as the cookie bakes. Thus, the more fat in a cookie dough, the more it will flow and spread. For this reason, pan-banging cookie recipes (like these chocolate chip ones popularized by Sarah Kieffer) contain more fat. The fat increases the fluidity of the dough so that we get dramatic ripples with every bang.

These pan-banging chocolate chip cookies form ridges because they are high in fat.

However, cookie spread is not just dependent on the amount of fat. Temperature is important, too. At low temperatures, for example, the fat molecules in butter form organized crystals, which makes the butter solid. But as temperatures increase, the crystal structure breaks down, and the butter becomes liquid. Liquid oils are affected by temperature, too. Although the difference isn’t as dramatic, they are thicker and more viscous at colder temperatures because the molecules flow more slowly. So no matter what fat you use in your cookies, the warmer it is, the more it moves, and the more the cookie spreads. Thus, cookie dough baked from room temperature spreads more than cookie dough baked straight from the freezer.

But in cookies that contain butter or shortening, temperature is often crucial for aeration. Many cookie recipes cream the butter and sugar together to add air to the dough. As we discussed, this step is crucial for tenderness. It also affects cookie spread—the more air we beat into the dough, the more the cookie expands and spreads. But creaming works best when the butter is at room temperature. So if we want to cream the butter correctly but limit cookie spread, we should start with room-temperature butter, then chill the finished cookie dough before baking.

Don’t forget that sugar and oven temperature also play a large part in cookie spread. So does your baking pan! Different materials and styles of pans vary in how they absorb and distribute heat, which changes the final cookie. (Tessa from Handle the Heat did a great demonstration here!)

The same cookie dough baked at different temperatures creates cookies with different textures.

Fats prevent sticking.

No matter what pan we use, we need to make sure our bakes don’t stick. Fat lubricates the bakeware, so recipes high in fat release more easily. Cookies, for example, rarely stick because they contain so much fat. Of course, we can also grease the pan to ensure a clean release. Any fat will work, but liquid oils tend to bead because the surface repels them. To get an even coating, nonstick sprays use the emulsifier lecithin. The emulsifier molecule contains a portion that’s attracted to the surface and a portion that dissolves fat. This allows the emulsifier to break the oil into smaller droplets and anchor them across a surface.

Once you’ve greased a pan, you can add parchment paper, or a coat of flour or cocoa powder as an extra barrier between the batter and the pan. Another option is to use two layers of fat, one solid and one liquid. For example, you can grease a pan with butter, let it solidify a little, then coat with oil or nonstick spray.

Fats increase the smoothness of candies.

As we discussed in the series on sugar, many candies, such as caramels, brittles, and fudge, are made from sugar crystals. The texture of the candy depends on the size of the crystals. A smooth fudge, for example, is achieved when the crystals remain small. When fats are added to sugar syrups, they lubricate tiny sugar crystals. This prevents them from clumping into larger crystals that would make a gritty fudge.

Fats lubricate sugar and prevent it from forming large, gritty crystals.

Fats thin chocolate.

Fats are also useful for adjusting the consistency of chocolate. At its core, chocolate is a mixture of solid cocoa particles in fat. When we make chocolate coatings, we often thin the chocolate with a little oil or butter. The extra fat lubricates the solids, helping them flow more easily. This helps create thin shells.

Fats adjust volume, spread, and consistency.

By greasing flour, proteins, sugar, and other solids, fats change the consistency of our baked goods. This property is used to make larger bread loaves, crisper cookies, smoother candy, and thinner chocolate. Fats are indispensable for greasing pans, too. Now that we’ve covered the slippery applications of fat, we’ll turn our attention to flavor in the next post.



References

Cook’s Illustrated. How to Make Your Metal Pans Naturally Nonstick.

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

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

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

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