Air film on the oil phase. Hall and Halstrom have reported that the presence of an air film on the oil phase, as it is introduced into the emul-sifier and forming emulsion in making mayonnaise, results in a less stable, inferior emulsion with lower specific gravity than in mayonnaise prepared with oil having no such air films. For the emulsions having air films on the oil, the oil was added from a buret at a definite rate, the point of the buret being six inches above the surface of the forming emulsion. For oil having no air film the buret point was lowered so that the oil was injected beneath the surface of the forming emulsion. They add, "Clayton predicted that when the dispersed phase is injected into the continuous medium below the surface, intermittent injection would confer no advantage." From their results Hall and Halstrom felt that Clayton's prediction was a sound one.

Water-holding capacity of emulsifier. Kilgore states that preserved yolks are available in five main conditions: frozen salted, frozen sugared, fresh refrigerated, especially treated, and dried. This is also the order of their volume consumption by the mayonnaise trade. Kilgore emphasizes that the starting mixture to which the oil is added should not contain too much "free" water. It should have enough "free" moisture to start emulsi-fication yet have a heavy body, like a thick paste, smooth in texture. Frozen and treated yolks, because they have more bound and less "free" water than fresh yolks, are excellent for starting mayonnaise to secure a fine "grain." Yet more of the frozen than of fresh yolks are necessary for an emulsion of good consistency. Kilgore adds that de-fatted mustard flour is an excellent water-holding ingredient; hence it gives a heavy paste and also has decided emulsifying powers.

Emulsifying properties of mustard. Kilgore determined the emulsifying properties of mustard in three ways: (1) Foaming ability, (2) the stability of oil drops on a mustard solution, and (3) the stability of emulsions made with mustard solution as the sole emulsifying agent. In a 75-pound batch of mayonnaise about 8 to 9 pounds of vinegar and 5 to 6 ounces of mustard are used, which gives about 3.5 per cent concentration of mustard. The concentrations of mustards used were: 0.1, 0.5, 1.0, 2.0, and 4.0 per cent.

Foaming. The mustard was weighed and added to water in glass-stoppered bottles and shaken. Little foam was formed except with the 2 and 4 per cent concentrations. Good emulsifiers for oil-in-water emulsions usually foam readily in water.

Oil drops on mustard solution. The mustard solutions were obtained by adding the mustard to water and filtering off the residues of undissolved mustard. About 70 per cent of the mustard was found to be soluble. If drops of oil such as corn oil are poured on water, they spread in a film over the surface of the water. But when drops of oil are placed on water containing an emulsifying agent which favors the formation of an oil-in-water emulsion, spreading does not occur. The drops remain separate and distinct. Kilgore found that a 1 per cent mustard solution afforded protection for the oil drops but a 4 per cent solution gave much greater protection.

Stability of mustard emulsions. The corn oil was added slowly to the mustard solution as in making mayonnaise, a high-speed drink mixer being used as a whip. After being stored for one year the emulsions made with 0.1, 0.5, and 1.0 per cent of mustard were broken. Those with 2.0 per cent had some oil on top; and the emulsion with 4.0 per cent mustard did not break and showed no leakage of oil, although it contained 80 per cent of oil.

Corran formed a water-in-oil emulsion of olive oil and lime water. To this emulsion mustard was added. When the concentration of mustard reached 2 per cent, the emulsion broke and reformed as an oil-in-water emulsion. Fine mustard flour was more efficient than coarse mustard flour.

Kilgore in continuing his work with mustard and emulsification found that mayonnaise without mustard had a stiffer consistency than that with a de-fatted mustard flour. But he found this depended on how the mustard was added. If added dry it decreased initial stiffness, but if added wet it increased the stiffness. De-fatted yellow mustard flour lost its emulsifying properties if mixed with vinegar and allowed to stand longer than a day; whereas this was not the case with mustard having a high oil content.

Emulsifying properties of oils. Meszaros states the size of the fat drops in an emulsion depends more on the method of preparation than on the properties of the fat. Meszaros has expressed the emulsification capacity in a number (E number) which represents the milligrams of fat which can be emulsified under certain conditions in 100 grams of water without the aid of emulsifying agents. Fats tested fall in four groups: (1) Fats which show a very good emulsification capacity (E number over 50); as goose fat, horse fat, lard, crude rapeseed oil (crude sunflower oil). (2) Good emulsifying fats (E number 20-50), as butter, butter fat, peanut oil, sesame oil. (3) Poor emulsifying fats (E number about 10) - coconut oil, palm-kernel oil, soybean oil, beef tallow. (4) Very poor emulsifying fats (E number 10) - illipe fat, hardened train oil.

The method of mixing. Kilgore, Corran, and Hall and Halstrom emphasize the method of adding the oil to secure a stable emulsion of desirable consistency. Hall and Halstrom found that the method they called the Compromise Method was the best. For this method a portion of the oil was added by means of a buret above or beneath the surface of the forming emulsion until optimum dispersion was obtained. They state that optimum dispersion might properly be considered the critical dispersion point. At this point maximum thickness is attained and any further addition of oil results in an irrecoverable breaking of the emulsion. This occurred after the addition of 30 to 35 cc. of oil to 20 grams of beaten egg yolk. At this point the vinegar and spices are added. This thins the emulsion but thickening occurs again with the addition of the remainder of the oil. The amount of oil added was such that the mayonnaise contained 89 to 93 per cent of oil.

For the method which Hall and Halstrom called American, the vinegar and spices were added to the egg yolk. After blending of these ingredients the oil was added in the same manner as for the compromise method. Their results follow:

Table 40 Stability of Mayonnaise (Hall and Halstrom)

Method

Manner in which oil was added

Stability of emulsion after storing at 8°C. for 2 years

Compromise.............

Above surface

Fragile, partially separated

Compromise.............

Beneath surface

No separation

American...............

Above surface

Complete separation

American...............

Beneath surface

No visible separation, but fragile

The emulsifying constituent of egg yolk. In starting their investigation, Snell, Olsen, and Kremers added lecithin to egg yolk in making mayonnaise. They acted under the general assumption that lecithin is the constituent of egg yolk which is effective in producing emulsions. Hence it was thought that the addition of more lecithin should increase the stability of the mayonnaise. But all the mayonnaises so produced had poor consistency. Next they studied the effect of each of the known major constituents of egg yolk on mayonnaise. It was found that none of these sub-stances was capable of producing the consistency derived from the whole egg yolk.

This led to the investigation which demonstrated that egg yolk owes its emulsifying action to an unstable complex containing both lecithin and protein, which they called "lecitho-protein." This lecitho-protein constituted about 32.5 per cent of the salted yolks.