Eggs. Eggs vary so in size that they should be weighed for experimental work. As previously stated, eggs beat up more quickly and to a better volume if they are not too cold, so that it is preferable to have them room rather than refrigerator temperature.

Methods of mixing cakes. There are many methods by which cakes may be mixed. Some old cake recipe directions state to mix the fat with the flour. The sugar is next added and lastly the eggs and milk. This old method may give very good cake. In all the batter and dough products that have thus far been considered, with the exception of cream puffs, the proportion of fat is usually smaller than in cakes. The method of mixing cream puffs is to melt the fat. It is also a common practise, except for biscuit, to melt the fat for the other dough and batter products. These same methods of mixing are used for cakes, but a new method is introduced, one in which a foam is formed with the fat. Certain procedures of mixing are designated by various names, but each of these methods may have many variations.

Conventional method. By the conventional method the fat and sugar are creamed until the mixture becomes lighter in color, spongy and fluffy in texture. Fig. 55 is a photomicrograph of creamed butter and sugar. The irregular, large, and intermediate-sized spheres are sugar crystals with an adsorbed layer of fat. It was difficult at first to decide whether the smaller rounded crystals were air bubbles or sugar. This was determined, as is often the case in experimental work, by accident. In using a microprojector to show slides made from colored creamed fats to a class the heat filter was forgotten. After a few seconds the heat from the light used in the projector melted the fat on the slide. One could watch the air bubbles burst on the screen. The remaining particles after the fat was melted were sugar crystals. Many of the air bubbles show in the picture as small, white circles with a very light gray line around them, and are hardly discernible at this magnification. This strong adsorption of the fat at the surface of sugar crystals and at the interface of air bubbles and a liquid is typical and is one means of distributing the fat throughout the batter.

It seems to make little difference in the final product if the fat is stirred for a short period and the sugar is then added gradually, or whether the sugar and fat are combined and then creamed, but air is incorporated more rapidly after the sugar is added. However, creaming by hand is easier and more rapid if the sugar is added gradually because the mixture is not so stiff.

In the conventional method the whole egg is creamed with the sugar and fat or only the yolk is incorporated during creaming and the beaten white is added to the batter. Not as much air can be introduced into the creamed mass if only the yolk is used, but this is compensated for in the cake volume by the air incorporated in the beaten white. Under some conditions there may be advantages in adding the beaten egg white last. Just as good texture is produced if the beaten white is stirred rapidly into the batter as when folded. The texture is also good if the beaten white is added and stirred in with the flour and milk. Considering time, effort, and the cake texture, there is often no advantage in separating the whites and yolks of the egg for plain cake.

Fig. 56 is a photomicrograph of the creamed butter-sugar-egg batter after the egg has been added. Since more of the sugar goes into solution the sugar crystals become smaller after the egg is added. Many of the sugar crystals are larger than those shown in this particular field, as will be noticed when the photomicrograph of the batter is observed.

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Fig. 55. - Photomicrograph of thoroughly creamed butter and sugar. The butter is stained and shows black in the picture. Note the rounding of the sugar crystals and adsorption of fat at their surface. Magnification approximately x 100.

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Fig. 56. - Same as Fig. 55 after the addition of beaten egg and thoroughly creaming. The sugar crystals are smaller due to water from egg partially dissolving the sugar. Note the many numerous small air bubbles. Most of them show white, but many show a thin gray line, which is the fat at the interface of the air, butter-egg-sugar mixture. Magnification approximately x 100.

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Fig. 57. - Cake made by method of mixing shown in Figs. 55, 56, and 58. The flour and milk were added alternately in thirds with a total of 225 strokes.

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Fig. 58. - Photomicrograph of cake batter. Same as Figs. 55 and 56 after flour and milk are added. There are many large sugar crystals in this field. The sugar crystals and gas bubbles with their adsorbed layer of fat are grouped rather uniformly. The air bubbles do not show at this magnification. If berry sugar is used instead of the coarser granulated sugar used in this illustration, the sugar crystals are smaller and more numerous, the cake texture improved. Magnification approximately x 100.

The Bakery Research Department of Procter & Gamble Company have reported that better results are obtained if the eggs are added gradually during 5 minutes, after the sugar and fat have previously been creamed 5 minutes, and the creaming is continued for a total of 20 minutes with a mixer. They state that if the eggs are added after the butter and sugar are thoroughly creamed there is a tendency to break down the creamed mass.

The flour and milk may be added to the creamed mixture as follows: (1) all added at one time, (2) flour added first and last, (3) milk added first and last, and (4) part of the flour and part of the milk added at the same time. Often the statement is given in directions for mixing cakes that a portion of flour should be added first and last to the creamed mixture, as the liquid tends to cause separation of the creamed mass. On the other hand, the Bakery Research Department of Procter & Gamble give for the method of mixing after the fat, sugar, and egg have been creamed, "to add two-thirds of the milk and mix it with just a few turns of the beater. Then the dry ingredients may be added and mixed in, using low speed. After the mixture is quite smooth, add the remainder of the milk slowly and continue the mixing until the dough is thoroughly mixed and very uniform." Judged from laboratory results, the first method is less likely to give an excellent texture, but all the others may give very fine even grain and velvety texture. Adding milk first and last is the quickest and easiest method.