This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
The addition of sugar to egg white foams. Adding sugar to the egg white increases the stability of the foam, for less drainage occurs when the egg is beaten to a definite stiffness. However, a longer time is required to beat the egg white, if the sugar is added before the beating is completed, but this also makes it difficult to overheat the foam. Because sugar retards denaturation of the egg white foam, it is a good practice to add sugar to the egg white as soon as beating is started when whites for angel cakes are whipped at high speed on a machine. It would also appear that less leakage might occur in meringues for pies if the sugar is added by beating it into the white as the white is beaten.
Egg white is partially coagulated during beating. In whipping the egg white is finely divided, so that from the physical subdivision it is far more rigid and stiff. But the beating has brought about other changes in the egg white. In speaking of the methods by which coagulation may be brought about, Ostwald states, "When egg white is beaten to a foam, a part is regularly coagulated in the walls enclosing the air bubbles. A decrease in degree of dispersion to the point of inducing coagulation can also be brought about through centrifuging, etc. These belong to the mechanical methods of producing coagulation."
Effect of temperature upon whipping of eggs. Since a low surface tension is one essential for the formation of a foam, it follows that a lowering of the surface tension will aid its formation. Eggs that are taken from the refrigerator and beaten while still cold do not whip up as readily or quickly as those at room temperature. Surface tension is lowered with increased temperature so that it is probably one factor in bringing about this result.
The Bakery Research Department of Procter & Gamble Company have reported that "regardless of the length of time of beating, a given sugar and egg mixture, when whipped at 60°F., will never become as light as will a mixture of the same proportions beaten at the same speed and at a temperature of 110°F."
St. John and Flor found that a greater volume was obtained at room temperature, about 21 °C, than at refrigerator temperature, 13°C. A still better volume was obtained at 30°C, but they report that while drying the whites to measure the volume the liquid part from those beaten at the highest temperature separated more readily.
Season and age of eggs and whipping. The whipping quality of eggs varies, according to the season in which they are produced. Nemetz has reported experiments in which whole eggs that had been broken and frozen in April, July, and September were used. The eggs were used in sponge cake and cream puffs. With all mixing and baking conditions standardized, the April eggs gave a 15 per cent increase and the September ones a 10 per cent increase in volume over the July eggs in sponge cake. Similar results were obtained in cream puffs.
Burke and Niles found that egg whites from eggs produced during the season when eggs are considered less desirable beat to a stiffer foam when beaten the same length of time than the whites from eggs produced early in the spring.
Nemetz states that if fresh or frozen eggs are used in a similar mix under identical conditions, greater volume and greater yield will be obtained from frozen eggs.
Bakers also claim that egg whites do not whip as well if used the next week after being frozen as when they have been frozen at least three months.
Barmore states that the older the eggs, when whites were beaten for equal lengths of time, i.e., 1, 2, and 3 minutes, the less stable the foam. However, when eggs were beaten 4 minutes the stability was practically the same for all ages of egg used, e.g., fresh, 3, 6, and 9 days.
Egg beaters. Egg whisks or whips are made with wires of varying thickness. The thick wire does not whip or divide the egg white as easily as the finer wire. The air cells are larger than when a whisk with finer wires is used, though the size of the enclosed air bubbles decreases with longer beating with any type of beater. Whisks with thicker wires may require two to four times as many strokes to beat an egg white to a definite stiffness as one with finer wires. Some egg whisks beat the egg quickly, dividing it into many very fine cells without giving an excess of the curdy-looking precipitate within the whipped white. Some produce a greater curdled appearance than others, even when the egg does not appear to be beaten to the same stage of stiffness. With the type of whisk that produces the very curdled appearance of the egg white, the cell walls of the omelet or souffle are more likely to collapse during baking, and, by many cell walls running together, a very coarse texture is obtained or the product falls. The above statements regarding whisks also apply to egg beaters of the rotary type. There is some variation in the width and the curvature of the blades of these beaters.
If the quotation concerning emulsifying apparatus, from Clayton, in the chapter on emulsions is changed to read, "It is quite reasonable to believe that for any given egg beater there exists an optimum speed or degree of agitation or beating, and an optimum time of beating, whereby the most perfect beaten egg white is obtained for a definite use," the statement may apply equally to egg beaters.
Longer experience only emphasizes the importance of the foregoing quotation from the chapter on emulsions. For instance, in the Foods Laboratory a procedure had been worked out whereby excellent angel cake is made by beating the egg white and adding the sugar, using high speed on the Kitchen Aid. The beating must be timed to the second, because with several hundred r. p. m. a few seconds too long makes a tremendous difference.
When Peet and Lowe began work on starting baked products in cold and preheated ovens, it was necessary to mix six times the angel cake recipe at one time. But it was found that the time of beating the egg whites on an institutional, large-sized Hobart mixer had to be increased over the time used with the Kitchen Aid to have the same stage of stiffness.
Bailey obtained larger volume from the thick portion of the white than from the thin part when whipped on a Hobart type mixer, but results were opposite on an electric Dover type.
Barmore states that with hand rotary beaters there was more reduction in viscosity for the corresponding reduction in specific gravity than with the electric beater used in his experiments. It has been the experience in this laboratory that Barmore's hand beaters 1 and 2 are poor types.
Hand-operated rotary beaters may be turned at varying speeds. But fast initial beating of egg white gives a larger volume to the egg white.
The gear ratio for hand-operated rotary beaters is about 1 to 5, i.e., one turn of the handle gives about 5 revolutions of the blades. If the handle is turned 120 r. p. m., the blades would turn about 600 revolutions. The speed of electric mixers, depending on the particular mixer, the speed, and for some mixers the load or stiffness of material used, may range from 300 to 2400 r. p. m.
Wire whisks or rotary beaters. One question that is constantly asked regarding the whipping of egg whites is whether it is better to beat them with a whisk or rotary beater. A great deal depends upon whether the egg whisk or rotary beater is a good type of its class or a poor one. If the eggs are whipped so that the cells in the cake are the same size there seems to be little difference in the finished product. Whisks sometimes give a larger volume than rotary beaters in angel cake.
Combination of egg albumin with metals. Sometimes in beating egg white a pink color develops. This is due to a combination of the egg albumin with a metal like copper or iron. The color develops more frequently when the acid cream of tartar is added, as in beating egg whites for angel cakes, but it may develop without its addition. Some egg beaters have blades of copper that are plated. After the plating is worn off the copper is exposed. The pink color has often been noticed when folding sugar into the beaten egg whites with a spatula. Probably some other factor than the presence of the metal alone is necessary to bring about the color change, for the color does not always develop when the egg whites are beaten with such beaters or when spatulas are used.