This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Salad dressing. The Food and Drug Administration has defined mayonnaise as being made with either egg yolk or whole egg. Hence, a product which may be similar to mayonnaise but stabilized with egg white, or part egg yolk and part starch paste, is called a salad dressing. Home-makers have used many emulsifying agents such as egg yolk, whole egg, egg white, cooked egg yolk, gelatin, starch paste, meat extract, and mashed potato. However, they are not equally efficient. The order for efficiency is as follows: egg yolk, whole egg, egg white, gelatin, and starch paste.
Fats such as butter and lard may be melted and substituted in a mayonnaise formula, but the product is a salad dressing. Mineral oil may also be used in a mayonnaise formula. Boiled salad dressings are also emulsions.
French dressings. French dressings are usually temporary emulsions, but some are quite stable. There, seems to be less separation of oil at the top and of water at the bottom, if the phase-volume rule is observed, and the oil composes about 74 per cent of the emulsion.. The seasonings, powdered paprika and mustard, are the emulsiflers. It is possible that traces of some substances in the vinegar may occasionally aid emulsification.
Emulsions stabilized with flour. In gravies and sauces the amount of oil that can be permanently emulsified is much smaller than in mayonnaise. Gravies and sauces in which the oil separates may be made smooth again by adding water and stirring while heating. The addition of water lessens the percentage of oil in the product. Emulsions stabilized with flour or starch need a higher percentage of water than mayonnaise. The starch absorbs a large portion of the liquid, which accounts for a large part of the water, but even if the maximum absorptive power of the starch is accounted for a large amount of water is still needed. This type of emulsion belongs in the class of hydrated colloids referred to by Fischer and Hooker, in which they state that the water must not be reduced below a lower limit and must not exceed an upper limit.
Cream puffs. Cream puffs are good examples of a batter in which the fat is emulsified. See Chapter XII (Batters And Doughs), Experiment 80. In the recipe as given in the experiment, the fat constitutes about 17 per cent of the uncooked ingredients, if the fat content of the butter is used as 85, the eggs as 10.5, and the flour as 1.5 per cent. The cooking of the water, flour, and fat will increase this percentage, as will the baking, on account of evaporation of water. The fat does not run or ooze out of the dough while the puffs are baking.
If the eggs in the recipe are reduced to 2 but no other change is made, Experiment 80C,2, the percentage of fat in uncooked materials is about 18.6. The fat in these puffs runs out of the dough and over the baking pan in large quantities while baking. With the smaller quantity of egg the emulsion does not hold, but if the amount of water added is increased to 1 1/4 cups when the eggs are reduced to 2, the amount of fat in the uncooked ingredients is about 17 per cent. The fat in these puffs does not ooze out while they are baking. Although the quantity of egg is important, this also shows that it is essential to have a definite proportion of liquid to prevent breaking of the emulsion.
Cakes. The fat in a cake batter may or may not be emulsified. A microscopic study of cake batters shows that there is a tendency for oils to be emulsified as oil-in-water emulsions, no matter what the method of mixing. Often the oil is not wholly emulsified, the degree of emulsification varying with the extent of mixing, the temperature, and other factors. When butter or hard fats are used in cakes or batter products, they may be partially or wholly emulsified, if they are melted before adding to the batter and provided the temperature of the batter is not so low as to chill the fat quickly; or they may be emulsified if the temperature of the ingredients is above the melting point of the fat, so that the fat is melted. In ordinary methods and temperatures of mixing cakes, the butter and hard fats do not give oil-in-water emulsions.