Freshness of Eggs
Coagulation
Aeration
Emulsification



This investigation introduces students to the changes which take place during storage with respect to both white and yolk. as well as changes which relate to air sac size.

The investigation enables students to:

• Examine the components of the egg and effects of short and longer-term storage.
  
  
• Relate results of calculations to the relative freshness of the egg components.
  
  
• Undertake sensory evaluation in relation to texture and odour analysis.
  
  
• Consider, by sensory evaluation, the acceptability of stored eggs by utilising them in a cooked dish.

Egg Quality Grading

European Union regulations state that from 2004 there will be two quality classifications of eggs, A and B:

Class A eggs are the highest of these and must be naturally clean, fresh, internally perfect and with intact shells.These are the eggs we buy in the shops for eating.

Class B eggs are used by food and other manufacturers.

Eggs which do not reach either of these two standards are classified as unfit for human consumption but are used by industry in products such as shampoo.


Practical Notes

• Ideally, a range of eggs could be used which have been stored for varying lengths of time, although only two storage periods have been suggested for comparison with the newly purchased egg. The two storage periods suggested are:
  
  a. An egg stored for two weeks in a domestic airing cupboard in which the cistern is kept hot. This will accelerate the changes in structure and illustrates the effect of extremes of temperature.
  
  b. An egg stored for two weeks under normal conditions in a refrigerator. By extending the range available it would be possible to provide pupils with an even clearer visual indication of changes which occur on storage.
  
  
• Eggs and their shells will be used for a number of tasks in this investigation. They should therefore be carefully labelled and retained.
  
  
• The sensory evaluation technique used is the simple selection of descriptors to describe aroma and texture.
  
  
• The chopping board is used throughout to support the eggs although a bench or work surface may be used. However, it is useful to use the chopping board in the section of the investigation where white and yolks are examined further. An egg cup may be used to contain the yolk to keep it on the board. whilst the board may be tilted to allow all the white to run off into the jug.
  
  
• Glass, china or stainless steel bowls should be used for whisking egg whites; aluminium bowls will cause discolouration of the egg white foam.
  
  
• A soufflé omelette has been chosen in order to use the eggs, particularly since egg white foams will be produced in the final section of the investigation. This enables students not only to use up the egg in a recipe which demonstrates useful practical skills, but also shows the acceptability of eggs even after prolonged storage. Eggs which have been assessed as non-consumable due to age should, of course, be discarded.
  
  
• The soufflé omelette recipe used in the investigation is obviously not the usual recipe as students will be starting with already whisked egg whites. The whisked egg whites will stand successfully with no leakage for a considerable time so that the soufflé omelettes should be quite acceptable.

The aim of this investigation is to study the effect of heat on eggs while at the same time producing a palatable dish for all the students. The finished product is assessed by sensory methods to decide which method of cooking produces the most acceptable result.

The investigation enables students to:

• Cook a savoury custard by one of four methods.
  
  
• Decide, by observing and tasting each of the finished products which method of cooking is the best for a baked custard.
  
  
• Relate the results of the investigation to the theory of coagulation.
  

Practical Notes

• Ideally, a wok would be used for stir-frying the vegetables but a frying pan is an adequate substitute.
  
  
• The custards cooked at 160°C, gas mark 3, will take quite a long while to cook - about 40 minutes. They could be cooked at 170°C, gas mark 4 or even 180°C, gas mark 5; in this case the temperature for other custards is increased to 200°C, gas mark 6. The important thing is that two should cook slowly and steadily and two should cook quickly.
  
  
• The descriptor 'porous' may need explanation. The main feature to look for is tiny holes that appear throughout the custard when it has been cooked too rapidly. This will be associated with loss of water from the coagulated egg mixture 'weeping' or syneresis.
  
  
• A problem with younger and less adventurous students may be an unwillingness to taste an unfamiliar dish. This savoury custard is in fact similar to the filling for a quiche which is a readily acceptable form of egg custard.

In general, egg dishes which are based on the coagulation property of egg are all 'custards' cooked to a lesser or higher degree. The word 'custard' however has a totally different sensory meaning to the world at large.

This investigation examines the ability of eggs to hold air and focuses in particular on egg white foams.

The investigation enables students to:

• Consider the method by which egg white foam is obtained.
  
  
• Observe the changes in egg white as foaming proceeds.
  
  
• Recognise optimum foaming for meringue formation.
  
  
• Examine the effects of methods by which sugar is incorporated into an egg white foam.
  
  
• Utilise hedonic ranking as a means of sensory evaluation.
  

Practical Notes

• It is desirable to produce a cooked base which utilises the egg yolk, is quick to prepare and cook and which can support the meringues. The recipe is a suggestion only, since other pudding bases may be developed according to personal tastes and individual recipe ideas.
  
  
• Each pair should produce all six variants or, if time does not allow, the work can be allocated between the pairs of students. It is essential that all six variants are available for assessment.
  
  
• An aluminium basin must not be used for whisking of egg whites since a discoloured foam will be produced.
  
  
• It is essential that students recognise the end point of whisking in foam formation. The test involving inversion of the bowl should be demonstrated. This will ensure uniformity and avoid disaster.
  
  
• The evaluation uses hedonic ranking. Only a 1-5 scale is suggested although a 1-9 scale may be substituted if a more detailed analysis is required; especially since students have experienced hedonic ranking on a five-point scale in Investigation 2.
  
  
• In order to determine the success of the meringue topping, some discussion may be required which identifies the desirable attributes of a meringue used in this type of recipe.

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.