Experimental cookery

CONCENTRATION OF OIL IN MAYONNAISE 285 phase run together destroys the emulsion. Over-heating, when the oil and liquid expand at different rates, the additions of salts, drying of the sur- face, freezing, and jarring may all cause separation in mayonnaise. The addition of enough salt (sodium chloride) to "salt out" the emulsifier will break emulsions stabilized with proteins, but this requires far more salt than is ordinarily used in mayonnaise. The amount commonly used aids in stabilizing the mayonnaise. Freezing dehydrates the egg, because the water separates from the egg protein in ice crystals, thus breaking the film. Agitation or shaking in shipping tends to break the emulsion. Evaporation from the surface of the mayonnaise may cause drying of the emulsifying agent and consequently coalescing of the oil on the surface. Mayonnaise keeps better in covered containers which prevent evaporation. Fischer and Hooker state that, if the protein emulsifier is diluted beyond the point at which it will take up all the water, the emulsion tends to break. Heating, resulting in too much evaporation of the liquid, causes separation of the fat in gravies, sauces, and cream pui¥s. Re-forming broken mayonnaise. The usual procedure to re-form broken mayonnaise is to take a new egg yolk and add the curdled, broken mayonnaise to this gradually. It is added and beaten in the same manner as when the oil is originally added to the egg yolk. But it is not necessary to use egg yolk to re-form the emulsion. It can be re-formed by adding the broken emulsion gradually to a tablespoon of water or vinegar. The broken emulsion must be added gradually to the water or vinegar and beaten during the addition. It will not re-form if the water or vinegar is added to the mass of broken emulsion. See Experiment 52, D. The Concentration of Oil in Mayonnaise The amount of oil that can be permanently emulsified varies with the emulsifier, the oil used, and the manner in which it is added. Pickering has emulsified "99 per cent of paraffin oil in 1 cc. of 1 per cent potash solu- tion by successive addition of small portions." The concentration of oil in food emulsions varies from a very low percentage up to about 85 per cent. Mayonnaise containing slightly more than 95 per cent of oil has been made in the laboratory, but it usually breaks shortly after a little more than 90 per cent of oil has been added. The stiffening of mayonnaise containing over 90 per cent of oil makes it difficult to mix the last addition of oil. Mayonnaise with more than 90 per cent of oil resembles jelly in consistency; cut with a knife or spoon it retains its shape. It will keep varying lengths of time in a covered jar in the refrigerator. Some break in a short time, but most of them keep for several days or weeks. Probably this variation in breaking is partially due to variations in beating in form- ing emulsions. After standing a short time, if the dressing is cut or if some is lifted out of the jar, there is a tendency for oil drops to form gradually 286 EMULSIONS