This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Extent of mixing, its effect upon crust and shape of cake. With very little mixing, so that the ingredients are just combined but not blended until the batter is smooth (cakes number 1, Figs. 68 to 70, with 50 strokes), the top of the cake is nearly level or slightly rounded. It browns well and is rough. The crust has considerable glaze. As the amount of mixing is increased the crust is less rough, has less glaze, does not brown so well, and is more rounded across the top, until with more than an optimum amount of beating, 300 to 400 strokes in this cake, the crust becomes dull in appearance and quite smooth. There is a tendency for the top to come to a peak instead of being rounded. Small holes may be notice-able. Over these holes there is often a very thin layer of crust that covers the end of a long tunnel that extends up through the cake. With decided excess of mixing, 1000 strokes, the top may be level or only slightly rounded and is very dull and smooth in appearance and nearly white in color. The appearance of the crust of cake made with sulfate-phosphate baking powder, Fig. 70, changes with increased mixing but not so rapidly as in the cakes made with the phosphate or tartrate baking powder.
Extent of mixing, its effect upon volume. When the cake is just mixed so that no dry ingredients show, the volume of the cake may be less than when the batter is stirred a little longer, or it may be larger. With more mixing, 100 to 150 strokes, the volume may or may not increase. Continued beating after an amount sufficient to give the maximum volume decreases the volume in proportion to the degree of over-mixing. With more than an optimum amount of mixing the volumes of cakes containing a phosphate or a tartrate baking powder decrease more rapidly than those of the cakes made with sulfate-phosphate baking powder. See Figs. 68 to 70.
Extent of mixing, its effect upon texture. With a definite proportion of ingredients the texture as well as the character of the crust and the volume varies with the extent of mixing. The cakes in which the ingredients are just mixed so as to show no dry flour do not have a desirable texture. See cakes 1 in illustrations. The ingredients of the cake are not well blended, and the crumb has a horny, flinty texture, which is sometimes called bready. The crumb is crumbly. It is not smooth and velvety on the palate. The cell walls are thick and the cells coarse and large in size. A cake made with this amount of mixing dries out and stales in a very much shorter time than portions of the same batter mixed for a longer time. With more mixing the grain of the cake is finer and the cell walls thinner. The crumb is smooth and velvety when tasted, and the ingredients are well blended. With a definite amount of mixing of the plain cake batter, 150 to 400 strokes, which varies somewhat with the kind of baking powder used, the maker's technic, and the temperature of the ingredients, tunnels begin to appear. More mixing than the optimum produces a finer grain, or smaller cells, until a stage is reached, 1000 strokes or more, at which the texture is very compact or even soggy and solid.
Swanson and Working, also Bailey and Le Vesconte, have shown that extended mixing of bread dough modifies the quality of the gluten, and its extensibility is decreased. It seems logical to expect this stage to develop in cakes as well as in bread, although on account of the different proportion of ingredients the amount of mixing to bring this about may vary from the amount required for bread. Several factors may aid in producing the small volume with 1000 strokes. These include the extent of mixing, its effect upon the gluten, the effect of the baking powder upon the gluten, and the loss of carbon dioxide formed from the baking powder.
Tunnels. Tunnels in cakes develop in the same way as the tunnels in muffins. Gas expands in a weakened section of the batter. This weaker section is between long parallel strands of gluten which have been stretched and developed in mixing and in putting the batter in the pans. An excess of flour, see Fig. 71, and too much mixing tend to favor the formation of tunnels. An increased percentage of sugar lessens the tendency to form tunnels. A high baking temperature may tend to increase the tendency for tunnel formation, but is quite variable. Tunnels are formed more often when small portions of the batter are baked in small deep pans than when the whole cake recipe is baked in a large or a shallow pan, for the batter for the small cake is usually dropped from a spoon, whereas for the larger cakes it is more often poured into the cake pan. Tunnels do not develop so often if the batter is stirred with a circular motion as they do when the batter is beaten across the bowl. The reason for this is that, if the batter is stirred, the mixing utensil is pulled around and around the bowl and after a definite amount of mixing the appearance of the batter
Fig. 70. - Showing the effect of extent of mixing on volume and texture when sulfate-phosphate baking powder is used. Experiment 84C. As shown in the illustration the cakes are about seven-ninths actual size.
150 grams of batter removed and baked after mixing, is similar to that in Fig. 71. When some of this batter is removed with a spoon to put in a cake pan, the spoon cuts across the strands or ridges developed during stirring, and tunnels are not so likely to occur in the baked cake. In beating, unless the bowl is turned while mixing, the strands or ridges have formed across the bowl instead of around it. If the spoon is dipped or the batter is poured in the same direction in which the strands are formed, the tendency to develop tunnels is augmented. If the bowl is turned while the batter is beaten, there is no more tendency for tunnels to form than when the batter is stirred.