Angel and sponge cakes are included under egg cookery because they logically belong here and not under batters and doughs. The texture of the finished cake depends chiefly upon the manipulation of the egg, and the cooking temperature corresponds to that used for egg cookery.

Review of literature on angel cake. Excellent work has been reported from different laboratories on angel and sponge cake and a review of this literature seems rather imperative.

Hunt and St. John separated the thick and the thin portion of egg whites. The average volume of the cakes from the thin portions was greater than for the cakes made from the thick portions. They have also reported that the volumes of angel food cakes made from egg whites beaten at room temperature, 21°C, were larger than cakes made from similar whites beaten at 5°C. The grain of the cakes made from whites beaten at room temperature was finer and the cakes more tender than those from whites beaten at 5°C.

Hedstrom, in studying the effect of the consistency of the egg white on the volume and texture of angel cakes, found the percentage of thin white increased, as did the pH, with increased age of the eggs. The effect of age of the eggs on the volume of the cakes is shown in Fig. 35. It is obvious that there are some discrepancies in these results. Nevertheless, they are given here, for further work, which is not complete, appears to substantiate these results in that cake volume decreases with increased age of the eggs.

Barmore's results of investigating the influence of chemical and physical factors on egg-white foams are as follows: stability of the foams was determined by beating the egg white with an electric food mixer and photographing the foams 2 and 10 minutes after beating had stopped. The specific gravity of foams was determined. Stability of the foams was further determined by placing the egg-white foam in a funnel and determining the drainage at definite intervals.

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Fig. 35. - Relation of angel cake volume to the age of the eggs. (Hedstrom.)

It was found that the older the eggs, the lighter the specific gravity of the foam after beating for a definite period of time. The addition of potassium acid tartrate, citric, and acetic acid increased the stability of the foams. The longer the foam is beaten, the less stable it becomes so that its stability is inversely proportional to its specific gravity.

Stanley states that the thin white beats up to a larger volume than the thick white. But the volume of the cake made from the thick white is larger than that made from the thin white and cakes made from the thick white have greater elasticity.

Barmore reported from his investigations on baking angel cake at various altitudes that increasing the egg or flour, or both, in an angel cake increases its tensile strength. Conversely, increasing the sugar decreases the tensile strength or increases the tenderness. Barmore says that his formula,

F - .43S - .41A + 24.5 = 0, gives all the possible, successful recipes for this type of flour mixture for any habitable altitude. F represents flour in grams; S, sugar in grams; and A, altitude in thousands of feet. The egg white was kept constant at 210 grams and the flour should be not less than 40 nor exceed 80 grams for this proportion of egg white. For 1 gram of egg white this allows 0.19 and 0.39 gram of flour respectively.

King, Morris, and Whiteman investigated "some methods and apparatus used in measuring the quality of eggs for cake making." The physical and chemical measurements made on the eggs were carbon dioxide content of the white and the yolk, pH and total solids on white, yolk, and magma, and viscosity of the magma. They say more work should be done on the relation between CO2 content and pH before it can be said that the increase in pH of the white is due entirely to a loss of CO2 The lifting power of the eggs was based on measurements of specific gravity and pH of the cake batter and on volume, tensile strength, and compressibility of the sponge cakes. They report that the chemical and physical properties of the eggs so far measured have shown no definite relation to the various cake measurements.

Barmore determined "the influence of various factors, including altitude, in the production of angel food cake." He concludes that the whites of fresh eggs should be beaten with 1 to 2 per cent of cream of tartar to a specific gravity of not less than 0.15 and not more than 0.17. Part or all of the sugar should be added before the addition of any of the flour, for the addition of the sugar strengthened the egg-white foam; whereas the volume of the batter decreased considerably more when the flour was added with the sugar than when it was added by itself, after the sugar had been beaten into the egg foam. A summary of Barmore's extensive investigations follows:

At pH 8 the stability of the egg-white foam was practically the same for acetic and citric acids and cream of tartar. But at pH 6 the cream of tartar produced the most stable foam.

Cakes baked at 178°C. for 30 minutes had larger volume, were more moist and more tender, probably because of larger volume, than cakes baked at 163°, 152°, or at 138°C. The last required 100 minutes for baking. Baking at the highest oven temperature produced an interior temperature about 2°C. higher than in cakes baked at the lowest temperature, though the difference in oven temperature was 40°C.

Eggs several days old made poorer cakes than fresh eggs. The reason suggested for this is hydrolysis of the egg proteins rather than increased proportion of thin whites.

No moisture was lost by evaporation by any portion of the cake farther from the outer edge than 1 cm. "Cake baked at the low temperature appeared to contain less moisture, because the center of the cake felt and tasted much drier than that baked at a higher temperature for a shorter time. The data show that one was just as moist in the center as the other. The difference in feel was apparently occasioned by the difference in the condition or location of the moisture. Perhaps in the low-temperature cake the moisture had been more completely removed from the sugar solution and absorbed by the starch or protein, because of the greater length of time the cake was maintained at a high temperature."