are usually referred to as crullers. Another is the beignet, a square-shaped doughnut covered with powdered sugar, commonly associated with New Orleans. Science Cake vs yeast style Yeast doughnuts and cake doughnuts contain most of the same ingredients, however, their structural differences arise from the type of flour and leavening agent used. In cake doughnuts, cake flour is used, and the resulting doughnut has a different texture because cake flour has a relatively low protein content of about 7 to 8 percent. In yeast doughnuts, a flour with a higher protein content of about 9 to 12 percent is used, resulting in a doughnut that is lighter and more airy. In addition, yeast doughnuts utilize yeast as a leavening agent. Specifically, "Yeast cells are thoroughly distributed throughout the dough and begin to feed on the sugar that is present ... carbon dioxide gas is generated, which raises the dough, making it light and porous." Whereas this process is biological, the leavening process in cake doughnuts is chemical. In cake doughnuts, the most common leavening agent is baking powder. Baking powder is essentially "baking soda with acid added. This neutralizes the base and produces more CO2 according to the following equation: NaHCO3 + H+ → Na+ + H2O + CO2." Physical structure The physical structure of the doughnut is created by the combination of flour, leavening agent, sugar, eggs, salt, water, shortening, milk solids, and additional components. The most important ingredients for creating the dough network are the flour and eggs. The main protein in flour is gluten, which is overall responsible for creating elastic dough because this protein acts as "coiled springs." The gluten network is composed of two separate molecules named glutenin and gliadin. Specifically, "the backbone of the gluten network likely consists of the largest glutenin molecules, or subunits, aligned and tightly linked to one another. These tightly linked glutenin subunits associate more loosely, along with gliadin, into larger gluten aggregates." The gluten strands than tangle and interact with other strands and other molecules, resulting in networks that provide the elasticity of the dough. In mixing, the gluten is developed when the force of the mixer draws the gluten from the wheat endosperm, allowing the gluten matrix to trap the gas cells. Molecular composition Eggs function as emulsifiers, foaming agents, and tenderizers in the dough. The egg white proteins, mainly ovalbumin, "function as structure formers. Egg solids, chiefly