Sponge cake, like angel cake and foamy omelets, depends chiefly upon the extent of whipping the egg whites, the mixing, and good proportions to produce a tender cake.

Probably the most common fault in making sponge cake is insufficient beating of the egg yolks and sugar. These two ingredients, plus the liquid, if water or lemon juice is used, can be beaten until they are extremely light and foamy. This is most successfully done with rapid beating, preferably by an electrically operated beater or a rotary beater rather than a whisk. Excellent sponge cakes may be made from only the yolks, provided some water is added and the yolks and sugar are beaten rapidly until very light. In the type of sponge cake recipe given in Experiment 70, when the flour is mixed too long with the sugar and egg yolks the cake is more compact and tough. But in some types of sponge cake in which considerable water is added, that is, the ones called water sponge, it is often necessary to beat the flour and egg yolks a long time to obtain a cake with thin cell walls and a uniform texture. In other words, this can be interpreted to mean that, for each recipe in which the proportion of ingredients varies from those in another recipe, the amount and the kind of manipulation to produce a cake of the best texture vary.

Different methods of combining the ingredients may be used in mixing sponge cake. Several are suggested in Experiment 70. Excellent sponge cakes may be made by any method of mixing. The method of adding the water and lemon juice to the sugar, given in Experiment 70,3, produces rather uniform results when used by many different students.

Platt and Kratz have reported means of measuring and recording some characteristics of test sponge cakes, which can also be used with angel cake. These include measuring tensile strength, volume, and specific gravity.

Whether the temperature for baking sponge cake like that for angel cake should be increased has not been reported. It has been shown in the author's laboratory that sponge cake made from egg yolks only is more desirable when baked at 350°F. than at 325°F. It is likely that most sponge cakes should be baked at the same temperatures as angel cake.