The Power of Flour, Part One of Two
Mar 6, 2010 | From the kitchen of Rose
For years I have been saying how important it is to use bleached flour in cake baking and I still prefer it, but after making the fortuitous mistake of using unbleached flour in a cake baked in a tube pan, and discovering that the pan's center tube kept it from falling, I have revisited the subject and made some very interesting and ground breaking discoveries.
Woody and I have conducted numerous tests using bleached cake flour, bleached all-purpose flour, and unbleached all-purpose flour in a solid (unmelted) butter layer cake using my one bowl mixing method and the All-Occasion Downy Yellow Cake from the Cake Bible. (We used two-thirds the recipe, first using two-thirds the baking powder (2-5/8 teaspoons). Then we decreased the baking powder to 2-1/2 teaspoons because we were using a 2" high pan instead of the 1-1/2" high pans in the Cake Bible (and higher pans need proportionately less baking powder). We found that when using bleached or unbleached all-purpose flour instead of cake flour, we got more tenderness (and in the case of unbleached flour improved flavor) by replacing 15% of the flour with potato starch which comes closer to cake flour than cornstarch.The overall appearance, however, with the bleached all-purpose flour is slightly lower either in height or in the center.
1. bleached cake flour is suitable for cakes where a very tender texture is desired.
2. bleached all-purpose flour and 15% potato starch to simulate cake flour results in a more even cake with smoother crust and better taste than cornstarch, but is not quite as tender.
3. bleached all-purpose flour is preferable for cakes that benefit from more structure.
4. bleached flour results in the best flavor.
5. bleached flour results in the best volume.
6. bleached flour results in the most tender and velvety texture.
7. unbleached flour results in less volume.
8. unbleached flour results in a coarser, chewier texture.
9. unbleached flour results in a cornbread-like flavor.
10. cornstarch substitution for part of the flour for bleached or unbleached all-purpose flour is less effective to improve structure than decreasing leavening, and alters the flavor.
11. potato starch substitution for part of the flour for bleached or unbleached all-purpose flour is even more effective than cornstarch as it softens the crumb. For the unbleached flour it also improves the flavor by lessening the cornbread-like quality.
At first I thought it was an inherent contradiction that unbleached flour, which is higher in protein, would result in less volume, which usually is an indicator of structural weakness, and yet be chewier, which usually is an indicator of greater structural strength. As I was going to sleep one night I was so disturbed by this thought that I pretended I was inside the structure of a cake and started picturing a mesh of wires like a metal fence. Then the thought hit me like lightening: If one were to snip those wires, the fence would collapse but if one tried to chew on those wires they would still be wires--hard and unyielding even though not strong enough to hold up as a fence structure! And then it seemed obvious that a cake made with the higher protein of unbleached flour would have a tougher but not necessarily stronger structure! (A good metaphor for defining how strength comes in different forms!) I then remembered what I had learned about the different types of gluten-forming protein contained in flour when I was working on recipes for The Bread Bible. One type of gluten is elastic and results in a more chewy texture. The other type of gluten is extensible (stretchy) and enables a bread or cake to rise higher without collapsing. Bleached flour also has a lower PH, which means it will gelatinize (set) more quickly and thus maintain its structure.
For bakers who either have no access to the bleached flour or prefer to use unbleached flour, Kate Coldrick's method of heat-treating flour in a microwave (Kate Flour) enables the flour to gelatinize more effectively and the addition of xanthan gum also strengthens the structure. But we wanted to see if there was a way to improve the performance of unbleached flour without heat-treating it. Our goal was to achieve the best volume, texture, and flavor, with no dipping in the center. [Note: the cake structure on the sides is slightly lower because the batter closer to the metal pan sets sooner than does the center. For a two-layer cake it is best to have level layers but for a single layer a slight dome is more attractive.]
Solutions & Options if Replacing Bleached Flour with Unbleached Flour
The customary technique to approximate cake flour when using bleached all-purpose flour is to replace 15% of the flour with cornstarch or potato starch. These starches gelatinize at lower temperatures (potato starch much lower than corn starch) than does the starch in flour, thereby improving the structure of the cake. We found that the cornstarch mixed with the bleached all-purpose flour resulted in a cake that was almost as tender as cake flour, and eliminated the slight dipping in the center. In the cake using UNbleached all-purpose flour the cornstarch decreased the over-all dipping by 1/8 inch but did not eliminate it. On the negative side however, in both cases the cornstarch resulted in a denser crumb, bubbly top crust and an off-flavor.
The potato starch totally eliminated the dipping! The crumb is slighty coarser than the bleached all-purpose flour, but the flavor is not compromised!
Photos of Cakes Using 2-5/8 Teaspoons Baking Powder
In our next series of tests, instead of cutting the bleached and unbleached all-purpose flour with cornstarch or potato starch, we lowered the baking power by 1/8 teaspoon (to 2-1/2 teaspoons per 200 grams/7ounces flour). Baking powder reacts with the liquid in the batter and the heat of the oven to produce bubbles that enlarge and ultimately disrupt the network structure of the batter. Flour that has greater elasticity allows the network to expand more before breaking, giving more time for the heat penetration to set the structure, preventing collapsing or dipping.
Decreasing the baking powder is less disruptive to the structure and thus completely prevented the cakes made with the all-purpose bleached and unbleached flour from dipping. It also resulted in better flavor than the cakes made with the addition of cornstarch. The texture of the cakes was slightly less tender but also less dense. To see if we could achieve the same tenderness of cake flour using all-purpose bleached flour with the correct lower amount of baking powder we tried one with the added cornstarch (see the third photo down) but it caused it to dip 1/4 inch.
Photos of Cakes Using 2-1/2 Teaspoons Baking Powder
Coming up Soon, Part Two: The Power of Leavening (Eggs versus Baking Powder)