This is the third in a series of 7 “Cake Batter” classes. We’ve been using the traditional “quatre quarts” pound cake recipe as a tool to understand the science of cake batter. In the first class we learned how mixing method affects cake texture. In the second class we learned how to use salt and chemical leavening to improve the cake texture and flavor. The remaining classes in this series will look at each of the original ingredients of the basic pound cake and their respective roles in the cake batter – flour will be up first.
The Baker’s Formula
A successful cake formula balances the four main ingredients-flour, sugar, fat and eggs. Although the quatre quarts recipe seems perfectly balanced because all the ingredients are of equal weight, through our testing we’ve seen that the original recipe does, in fact, make a cake that’s sorta dry, dense and not quite sweet enough for modern tastes.
Each of those ingredients has an important role in the recipe. The flour and eggs form the structure of the cake with a network of proteins and starch. Butter and sugar provide flavor and moisture, but weaken the cake’s structure.
In a successful cake, the ingredients that strengthen the cake structure (flour and eggs) are balanced with the ingredients that weaken the cake structure (sugar and fat). Too much flour and/or eggs will make a cake that is dry and tough. Too much sugar and/or fat will make a cake batter that will not set properly and may even collapse. To create a moist, sweet and tender cake that bakes up with a nice even crumb the four main ingredients have to work together.
So let’s look at the flour. Specifically, wheat flour. Although the four ingredients of the quatre quarts are equal in weight, the flour has the greatest volume.
All About Flour
Wheat flour is composed of proteins, starch, lipids, sugars and enzymes. The two most important of these components, the starch and the protein, form the cake “crumb”. The cake crumb is a network of starch and protein interspersed with millions of tiny air bubbles.
Wheat flour is about 70% starch. Starch granules absorb water from the batter, swell up, and gel. As the cake bakes, the gelled starch sets to help form the physical structure of the cake.
Protein is the other major component of wheat flour. When cake batter is mixed, two proteins in the dry flour, glutenin and gliadin, absorb water and form gluten. Gluten is a network of coiled and folded protein strands. The stronger the gluten, the more water it will absorb. If you replace a low protein flour with an equal volume of high protein flour the batter will be much thicker, since the stronger gluten will absorb more of the available water. Using a higher protein flour changes the outcome of the recipe not only because the gluten is tougher, but also because there is less water available to the other ingredients in the batter.
As a batter or dough is mixed or kneaded the coiled and folded strands of gluten begin to align and tighten. This is why a bread dough that starts out loose and “shaggy” becomes smooth and silky as it is kneaded.
For cake batter, stronger gluten is not desirable so we have to limit it’s formation. How do we do that? We’ve already taken a few steps with our recipe to impede the gluten formation. The reverse creaming method limits gluten formation by coating the flour proteins with fat before liquid is added. Limiting the amount of salt in the recipe helps, since salt will strengthen gluten. The easiest way to control the amount of gluten in the cake batter is to use a flour with a lower protein content.
Types of Wheat Flour:
“Spring Wheat” is high in protein and low in starch. When this high protein wheat is milled, the hard kernels break into large chunks that will form a strong gluten network when they come in contact with water.
“Winter Wheat” has a lower protein content and higher starch content. When low protein wheat is milled, the soft kernels break into very fine particles. Winter wheat produces a fine and silky flour that forms a weak gluten network when it comes in contact with water.
Bread flour contains more of the high protein spring wheat and cake flour contains more of the low protein winter wheat. All purpose flour is a mix of both types of wheat and has a medium protein content. Whole wheat flour is similar in protein content to all-purpose flour, but the bran and germ are left in the flour.
An equal volume of two different flours may not be equal by weight. For example, one cup of cake flour weighs about 4.25-4.5 oz and 1 cup of bread flour weighs about 5.25-5.5 oz (using the “dip and sweep” method). Those differences are important to remember if you switch out one type of flour for another in a recipe that uses volume measurement rather than weight measurement.
The obvious choice for cake bakers is cake flour, made from low protein, soft wheat. Not only is cake flour desirable because of the lower protein content, it’s desirable because it’s chlorinated. Chlorination makes cake flour slightly acidic, which weakens the gluten. Chlorination also alters the starch so that it can absorb more liquid and allows the fat in the batter to bind better with the starch. A cake made with chlorinated flour has a stronger starch gel, a weaker gluten network and very evenly distributed fat molecules. The result is a cake with a tender and fine crumb.
In a pinch you can substitute all purpose flour for cake flour. For each cup of cake flour use ¾ cup of all purpose flour plus 2 tablespoons of corn starch. This will lower the protein content, but the results will not be exactly the same since all purpose flour is not chlorinated.
To make a chocolate cake you can replace some of the flour in the recipe with cocoa. Cocoa has starch and protein so it will absorb some water and contribute to the cake structure, as flour does. Replace equal amounts of flour with cocoa. For example, if you add 2 oz of cocoa reduce the flour by 2 oz.
The Protein Content and Weight Varies by Type of Flour:
Cake Flour is 7-8% protein and 8 oz = 1 ¾ cup
Bleached All Purpose Flouris 9.5-12% protein and 8 oz = 1 ½ cups
Unbleached All Purpose Flour is 11-12% protein and 8 oz = 1 ½ cups
Bread Flour is 12-13% protein and 8 oz = 1 ½ cups minus 1 tablespoon
Whole Wheat Flour is 11-15% protein and 8 oz = 1 ½ cups
Baking a Gluten-Free Pound Cake:
With the rising interest in gluten-free baking, I thought I should try baking the pound cake recipe with a commercially prepared gluten-free flour. Although a lot of our efforts with the pound cake recipe have been to avoid forming too much gluten in the batter, some gluten is needed to give the cake it’s structure. Gluten-free recipes use non-wheat flours that don’t contain gluten. When using gluten-free flour, a binding agent must be added to the batter to replace the elasticity lost without the presence of the wheat flour protein.
The flour I used contains rice flour, potato starch, pea fiber, tapioca starch and xanthan gum. The xanthan gum acts as a binder to replace the structure provided by wheat gluten.
First I made our pound cake recipe using the reverse creaming method. The cake made with the gluten-free flour was significantly flatter than the cakes baked with wheat flour. This was not surprising since gluten helps the cake keep it’s shape while it rises in the oven. Without gluten the structure is weaker so the gluten-free cake can’t rise as high as a cake made with wheat flour.
Since I didn’t have to worry about gluten toughening the cake crumb, I tried mixing the cake using the creaming method to incorporate more air bubbles and, hopefully, get some extra rise on the cake. The second test was more successful. The gluten-free cake made with the creaming method baked up a little higher and lighter than the cake made with the reverse creaming method. Once again showing that mixing method does matter for successful baking.
In the next class we’ll learn all about eggs in cake batter.