1446 The Cornell Reading-Courses 



On the amount of air entangled in the eggs and held up by the gluteti 

 in the flour depends the hghtness of cakes of the sponge-cake type, which, 

 after all, are a form of omelet rather than of cake. In this type of cake 

 no baking powder is needed, because the air included in the eggs is sufflcient 

 to lighten the comparatively small quantity of flour used. For this reason, 

 in making sponge cakes the yolks and whites of the eggs are beaten 

 separately, so as to include as much air as possible in the whites. The 

 whites should be beaten until they are stiff, but not too dry, other\vise 

 some of the air cells will be ruptured and the cake will shrink more than 

 it should when taken from the oven. 



Effect of heat on eggs 



The coagulation of eggs takes place at a comparatively low temperature, 

 and they are toughened if cooked too long or at too high a temperature; 

 hence the necessity of a moderate oven if the sponge or angel cake is to 

 rise to its fullest height and be tender. The addition of cream of tartar 

 or of lemon juice helps the egg to coagulate at a still lower temperature 

 than it otherwise would, and also probably dissolves some of the gluten 

 of the flour, thus helping to make the cake tender. On the other hand, 

 too cool an oven causes the sponge cake to expand until it is very light, 

 and then to fall because there is not sufficient heat to cause the cake to 

 harden; or else the cake does not bake through, and, although sufficiently 

 cooked on the outside, is raw in the center. 



Effect of beating an egg 



The question is often asked why the yolks of eggs cannot be beaten 

 as light as can the whites. One third of the yolk of an egg consists of 

 fat, and the presence of fat prevents the yolks from being elastic enough 

 to entangle and hold air. For the same reason, when the white of the 

 egg is mixed with the yolk the mixture cannot be beaten to a stiff 

 lightness. 



Effect of increasing or decreasing egg substance in cakes 



If a cake recipe is altered so that additional egg whites are used in the 

 place of egg yolks, more fat should be added, the proportion being one tea- 

 spoonful of fat for each additional white. If the number of eggs in a cake 

 is increased, the amount of baking powder should be decreased, provided 

 the quantity of flour and sugar remains in the same proportion. A general 

 statement may be made to the effect that one teaspoonful of baking 

 powder will replace one egg. This is illustrated in formula I as compared 

 with formula IV (page 1457)- 



