Flour is not an ingredient to be taken lightly. Use the wrong type in your baked good and you may end up with a tough cookie, a chewy cake or a flat baguette. The main difference in flours comes down to the amount of protein each type contains. Cake flour is lower in gluten-forming proteins, which makes it produce tender, light batters. All-purpose flour is higher in these proteins, so it yields baked goods, such as hearty breads, with a bit more chew.
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How Wheat Is Processed
The strain of wheat that millers choose to process affects the protein content and quality of the flour. When wheat is made into flour, the germ and bran are removed to reveal the endosperm. These endosperms are then processed through rollers over and over again to sift them into streams. Shirley Corriher, in her food science bible Cookwise, notes that one endosperm may be divided into 80 or more streams, each of which is analyzed for its qualities such as softness and protein content. A miller looking to make all-purpose flour will select streams that contain more protein, while a cake-flour miller will opt for the streams with less protein.
The protein in flour combines with water and heat to make gluten, which gives baked goods body and heft. The more protein in a flour, the more gluten is created, and the chewier and denser the final product becomes.
Cake flour contains about 8 grams of protein per cup, which amounts to 7.5 to 8.5 percent total. This protein content yields a sorry loaf of bread, but provides you with light and tender cakes, quick breads, muffins and pancakes. Pie crusts, dumplings and _genoise_s -- eggy, light cakes -- also do best when made with cake flour.
All-purpose flour contains between 11 and 13 grams of protein per cup, which amounts to 9.5 to 12 percent total. This high protein content weighs down delicate baked goods, making them tough and short. Yeast breads, strudel, cream puffs, puff pastry and pasta are doughs that require elasticity and strength, and thus benefit from using higher protein flours, like all-purpose. Cookies, dense and fruit or vegetable quick breads, and high-fiber muffins also do well with all-purpose flour. If you're making hearty, dense yeast breads, bread flour is even better than all-purpose, as it has an even higher protein content of 13 to 14 percent.