The use and effectiveness of egg yolk to stabilise an emulsion is investigated here. This is done by making mayonnaise using three different proportions of oil to aqueous phase (vinegar) and also by using a different method.

The investigation enables students to:

• Make mayonnaise by one of four methods.
• Assess the quality of the mayonnaise by considering various sensory attributes and its overall acceptability.
• Observe the longer-term stabilisation effect of the mayonnaise.

Practical notes

The emulsifying agent in egg yolks is lecithin.

Four groups are suggested: these can consist of one student or pairs. The groups can be repeated depending on the number of students in the class.

A minimum number of ingredients are used in this mayonnaise: suggestions for others such as mustard and mixed herbs are expected in answer to the question in Results (4).

Groups 1, 2 and 3 should all result in smoothly-mixed mayonnaise, depending on the speed with which the oil is added. The consistency will, however, vary. The mayonnaise made by Group 4 will be curdled because the oil is added too quickly for the emulsifying agent to stabilise the two phases.

The Department of Health currently advises that raw eggs should not be eaten. Recipes such as mayonnaise should only be consumed when they have been made with pasteurised eggs.