Briefing

An emulsion is made up of one liquid dispersed in another. The most common emulsions are water-in-oil (eg: margarine) and oil-in-water (eg: egg yolk).

The dispersion will only remain stable if it contains an emulsifying agent, that is; a substance attracted to both phases. Since eggs do not separate into oil and water even during lengthy storage, the yolk must contain a powerful emulsifying and stabilising agent. If it is so powerful within the egg, it seems likely that the yolks themselves can be used to emulsify and stabilise other emulsions.

How effective is the agent in egg yolk in stabilising the emulsion in mayonnaise?

Work in four groups.

Each group requires:

• 1 litre basin
  
  
• Tea towel
  
  
• Hand or (preferably) electric whisk
  
  
• Measuring cylinder
  
  
• Wooden spoon
  
  
• Wine glass or small tumbler
  
  
• Cling film
  
  
• Tablespoon
  
  
• Sticky labels
  

Method

		Mix the yolks and salt and pepper together in the bowl.
		Groups 1, 2 and 3: pour in the oil as SLOWLY as possible - 1 drop at a time is best - and whisk continuously. Group 4: add all the oil at once to the seasoned yolk THEN whisk. All groups: continue whisking until all the oil is added and the mixture thickens and becomes lighter in colour.
		Add the vinegar gradually (but more quickly than the oil for Groups 1, 2 and 3) and mix with the wooden spoon.
		Label the different mayonnaises clearly.

Results

		Look at the COLOUR of the mayonnaise. It should be very pale yellow. Rank the four samples of mayonnaise in order of acceptability: 1 (most acceptable) made by Group           2 made by Group           3 made by Group           4 (least acceptable) made by Group
		Look at the TEXTURE of the mayonnaise. It should be smooth, thick and creamy. It should NOT be curdled, separated or greasy. Rate each mayonnaise on a 1-5 hedonic scale as follows: Group 1 Group 2 Group 3 Group 4 1 like extremely         2 like moderately         3 neither like nor dislike         4 dislike moderately         5 dislike extremely

• Consider the OVERALL ACCEPTABILITY of the four mayonnaises. Which do you think is best and why?
  
  
• What additions would you make if they were to be used for a savoury dish such as coleslaw or egg mayonnaise?
  
  
• Put a tablespoon of each mayonnaise into each of four labelled glasses and cover with cling film. Leave to stand in the refrigerator for a day. Is there any separation? Now leave for a week - is there any separation?

Using the mayonnaise to make a chocolate cake

The mayonnaise samples can be used to make coleslaw or egg mayonnaise. However, there are other ways in which mayonnaise can be used and it is suggested that all the samples are used to make mayonnaise chocolate cakes.

Work in groups to produce four chocolate cakes to be evaluated.

Materials

• 125g self raising flour, sifted
  
  
• 1 teaspoon baking powder
  
  
• 100g sugar
  
  
• 100ml mayonnaise
  
  
• 2 x 15ml spoons cocoa
  
  
• 100ml boiling water
  
  
• Jam (optional)
  
  
• Mixing bowl
  
  
• Weighing scales
  
  
• Wooden spoon
  
  
• 20cm sandwich tin - greased and lined
  
  
• Teaspoon
  
  
• Tablespoon
  
  
• Measuring jug
  
  
• Knife
  
  
• Wire cooling tray
  

Results

When the cakes are cooled, evaluate them for APPEARANCE, TEXTURE and TASTE on a 5 point scale.

1 like extremely
2 like moderately
3 neither like nor dislike
4 dislike moderately
5 dislike extremely


Hedonic Ranking Results

• Comment on the acceptability of each of the mayonnaise chocolate cakes.