In making mayonnaise, several factors affect the formation of the emulsion, its stability, and ease of making. The major factors may be listed as follows: (1) degree and kind of agitation, (2) the method of mixing, (3) the ingredients used, and (4) temperature. Some of these may be further subdivided.

Degree and kind of agitation. This factor has already been partially discussed. Under it can be included the kind of apparatus used as well as rate of agitation. Good stable mayonnaises may be formed by both continuous and intermittent agitation. Hall and Halstrom have demonstrated that very stable concentrated mayonnaise may be formed by continuous agitation if the oil is added beneath the surface of the forming emulsion. Clayton states that it is a well-known fact that agitation can both make and break an emulsion. It has often been observed in the laboratory, when the vinegar and seasoning have been added to the egg yolk before any oil is added, that rapid agitation for the first additions of oil is advantageous; otherwise the resulting mayonnaise is less viscous.

The kind of bowl used. Some failures in making mayonnaise are due to putting small quantities of the egg yolk in a large mixing bowl. As a result the egg yolk spreads out in such a thin layer that the egg beater picks up very little of the egg and an emulsion is not formed with the first portions of the oil added. Sometimes the rod at the bottom of the rotary egg beater is thick and holds the beater above the contents of the bowl, provided the quantity of material in the bowl is small and the egg beater is held upright.

The method of mixing. Under the method of mixing may be grouped the following: (1) the method of adding the oil, (2) the quantity of oil that is added at first, (3) the time of adding the vinegar, and (4) the time the seasonings are added.

The method of adding the oil. Hall and Halstrom have shown that a more stable emulsion is formed when the oil is added beneath the surface of the forming emulsion.

The quantity of oil that is added at first. Often the statement is seen that mayonnaise can be made by putting all the ingredients in the mixing bowl and then beating. The author (see Experiment 52C,3) has never been able to do this and has never witnessed the making of it in this way. Many water-and-oil emulsions can be made by putting all the ingredients together and shaking or stirring, but mayonnaise does not seem to belong to this group. It is possible that some factors may occasionally influence the formation of an emulsion so that it is formed when all the ingredients are added at once to make mayonnaise.

Mark expresses the amount of oil that can be added and an emulsion obtained as follows: "(1) If the proportion of oil to that of egg or of the emulsion already produced was kept below a certain maximum a stable emulsion always resulted, no matter what the temperature or manner of beating, (2) that if the proportion of oil added exceeded a certain maximum, the egg or the emulsion already formed became dispersed in oil and no permanent emulsion was formed, (3) that if the proportion between these limits were used a permanent emulsion might or might not be formed, dependent on such variables as manner of beating and temperature, (4) that if egg was previously diluted by adding vinegar the proportion of oil which could be permanently emulsified was greatly increased during the addition of the first and second portions of oil, but that as viscosity of the mixture increased the maximum ratio of oil to emulsion rapidly approached the value found when egg alone was used at first."

Mayonnaise is formed more readily if the quantity of oil added at first is small. But the quantity of oil that can be added to egg yolk for the first addition of oil and still obtain a stable emulsion depends somewhat upon the rate of agitation, the combined volume of egg yolk and vinegar, the temperature of the ingredients, and other factors. If the above factors are standardized and if the combined volume of the vinegar and the egg yolk is 1/4 cup, the quantity of oil that can be added and emulsified is a definite quantity. If the combined egg yolk and vinegar is 1/2 cup, the quantity of oil that can be added will be 2 times as much as for 1/4 cup under the same conditions. Using 1 egg yolk and 15 cc. of vinegar and beating with a rotary egg beater in a round-bottomed jar, Experiment 52C, 2, 12 tea-spoons of oil have been the limit for the first addition of oil. Often only 10 or 11 teaspoons can be added. This large quantity of oil must be carefully emulsified before the second portion of oil is added. The volume of the egg yolk and vinegar is a little over 2 tablespoons. Thus the volume of oil that can be added, 7 to 10 teaspoons, is about the same as the volume of the egg yolk plus the vinegar. The emulsion is formed more easily if smaller quantities, 2 to 3 teaspoons, of oil are added at first. The second addition of oil, and any subsequent addition, must not exceed a definite relation to the volume of emulsion already formed. In making salad dressing with 1 egg, 1 cup of cornstarch paste, a cup of oil, and vinegar, all the oil can be added at first, but here again the volume of the oil is about the same as that of the emulsifier, i.e., the egg yolk plus the cornstarch paste.

The time of adding the vinegar. Part or all of the vinegar may be added at various intervals during the mixing or it may be added to the egg yolk alternately with the oil. It may be added after considerable oil is added to the egg yolk (Experiment 52A,1,2,3) or before any oil is added. By the last method the oil may be added in larger quantities for the first and second additions, and the mayonnaise made more rapidly. However, the size of the oil particles that are first emulsified is quite large when the vinegar is added to the egg yolk before the oil is added. But with each subsequent addition of oil the dispersed particles become smaller, and the mayonnaise stiffen This is shown in Figs. 27 to 30, which are photomicrographs of mayonnaise. If the oil is added to the egg yolk before the vinegar, the first oil particles emulsified are very small and remain small with subsequent additions of oil. When the vinegar is added, the dispersed globules become larger, and the mayonnaise less stiff.