This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
The method of mixing the ingredients. Bingham states, "A pure liquid, at a given temperature and pressure, can have but a single fluidity, but in our study of liquid mixtures we have seen that a mixture of liquids may have an indefinite number of fluidities dependent upon the method of mixing, in other words, upon the structure of the liquid. Since colloidal solutions are always heterogeneous, they always possess structure, and therefore we have this variable always entering into our consideration, whereas heretofore we have given it but scant attention. There is, however, every gradation from a pure liquid, to an incompletely mixed solution, an emulsion, suspension or typical gel."
Methods of mixing and order of combination of ingredients have been important in many of the products that have been studied, i.e., gelatin, emulsions, milk, and egg cookery. The methods of mixing are particularly important in the batter and dough series. In some doughs, like pastry and biscuits, the fat is first blended with the flour, and the liquid is then added; in other instances the liquid ingredients are mixed and the flour added to them. Many different methods of mixing may be used with cakes. They will be discussed in more detail later.
A microscopic study of the distribution of the fat by different methods of mixing shows many gradations from the fat distributed in very thin films to that in thick layers. Sometimes the fat or oil is completely emulsified, sometimes only partially. The sugar may be partially dissolved, "an incompletely mixed solution," or completely dissolved. One can see that it is not strange that cakes and other batter products are not always identically alike with different bakings. Different methods of mixing may give different results, but from the previous discussion one concludes that a person cannot state definitely of a muffin, biscuit, or cake, that its texture is due to the method of mixing alone, for the extent of mixing, the temperature of the ingredients, interfacial reactions, and other factors influence the texture obtained.
The effect of extent of mixing on the flavor of dough and batter products. The statement that a cake from one-half of a batter after the ingredients are barely mixed does not have the same flavor as a cake baked from the other half of the batter after a longer mixing may seem strange at first. But with longer mixing the sugar is better dissolved, and the other ingredients better blended. To prevent repetition in the discussion of specific batter and dough products, flavor is seldom discussed. But from the standpoint of eating quality, flavor is of great importance, and on a score card the author would rate flavor higher than texture, appearance, or tenderness. However, in the dough and batter series good flavor and good texture are closely related, i.e., if the texture is excellent the flavor is also usually rated high. Of course this is presuming that the ingredients used are of good quality and flavor, and that good proportions are used, i.e., too much salt is not added, etc. Unless otherwise stated, it is considered that the conditions that produce the best texture also give the best flavor.
The role the various ingredients play in batter products. Liquid. The liquid is a solvent for sugar, soluble salts, and proteins. It is through solution in the liquid that the chemical reaction of baking powder is brought about with release of CO2. The liquid hydrates the flour and egg proteins, giving the flour proteins cohesiveness and increasing the extensibility of proteins. Sugar in solution in the liquid comes in closer contact with proteins. The absorption and consequent swelling of starch granules gives them adhesiveness and cohesiveness and aids in forming the frame-work of baked products.
Flour. Flour forms the framework, the backbone, or skeleton of baked products. This framework is more or less modified by the other ingredients. The gluten forms a continuous network, and the starch granules, which swell to a greater or less extent, depending on the proportion of liquid, become more or less adhesive and are embedded in the gluten network.
Fat. Fat renders a product tender or short. It is not soluble but is adsorbed strongly on the surface of other constituents and forms films separating and lubricating them. In this way it is one of the major factors in producing a velvety, soft crumb in cake. Fat adds richness and tends to decrease the volume. If creamed it is a means of incorporating air, thus increasing the porosity.
Sugar. Sugar adds flavor. In increasing amounts up to the optimum it tends to increase the volume and tenderness of the product to which it is added. Fat is strongly adsorbed by sugar crystals and is thus distributed throughout the batter. Sugar peptizes egg and possibly flour proteins, elevating the coagulation temperature of these proteins. In increasing amounts it delays solution of baking powder and other salts, so that carbon dioxide is produced more slowly. It is also possible that it may tend to absorb some of the carbon dioxide, thus lessening the amount lost during mixing. Because it is somewhat porous it may be a means of adding more air to the batter.
Egg. Egg adds flavor and additional protein for the framework. If the yolk and white are not separated, the egg tends to decrease the volume and increase the elasticity and rubberiness. The lecithio-protein of the egg yolk has strong emulsifying properties and in batters emulsifies all or a major portion of the oil or melted fat. When the white is separated from the yolk it can be used as a means of incorporating air, thus increasing the volume and tenderness of the product. Well-beaten whole egg can also be used as a means of incorporating air, if added quickly to the batter before the air is lost.
Baking powder. Baking powder in optimum amounts increases the porosity of products and, by stretching the elastic protein, thinner cell walls, more tender products, and products of larger volume are obtained. It is possible that ions of salts of the baking powder or their residual salts may modify the hydration capacity of the flour proteins and some ions may tend to peptize some proteins.