EGGS

We consume the eggs of birds like consume the eggs of birds like hen, goose, turkey, fowls etc. The eggs of only those birds whose meat is eaten are used for cooking purposes. But in India, eggs of hen and ducks are used. Eggs serve a versatile and basic function in diet and in food preparation. They are a pre-packaged container of nutrients in their own disposable shell.

Grading of eggs
(U.S. weight classes for eggs, minimum weight per dozen for each size)

Jumbo Extra large Large Medium Small Peewee
30 oz/
75 Gms/egg
(900 Gms per dozen) 27 oz/
68.5 Gms/egg
(810 Gms per dozen) 24 oz/
60 Gms/egg
(720 Gms per dozen) 21 oz/
52.5 Gms/egg
(630 Gms per dozen) 18 oz/
45 Gms/egg
(540 Gms per dozen) 15 oz/
37.5 Gms/egg
(450 Gms per dozen)
N.B.:1 oz=30 Gms approx.

Structure of eggs

Structure of an Egg

The egg is composed of shell, white and yolk. The egg white forms 2/3rd of the whole egg and the yolk forms 1/3rd.
1. Shell
It is the outer hard covering of the egg and is made up of Calcium, Magnesium carbonate and Calcium phosphate. The shell gives shape to the egg and holds the inner contents. The shell contains thousands of pores that allow CO2 and moisture to escape, as well as air to enter. The shell is covered by a cuticle membrane or Bloom and should not be washed. The bloom acts as protective covering blocking the pores, and prevents moisture loss and bacterial contamination. When eggs are washed before going to the market, the cuticle is removed. To protect the egg, the washed eggs are coated with a thin film of edible oil.
2. Membrane
Beneath the shell, there are two semi permeable membranes - the outer and the inner. These membranes act as a protective layer in case the shell cracks.
3. Air cell
On one side of the egg (broader), both these membranes separate to form an air cell. This is formed by contraction of the contents as soon as the egg is laid, due to the difference in the outside temperature.
4. Egg white
It has 1/8th part of the protein, which is called albumin; the remaining being water. The egg white consists of three parts – the outer thin albumen, the middle thick albumin and the inner thin albumin.
5. Egg yolk
The yolk is separated from the white by a membrane called vitelline membrane. This membrane prevents the mix of both yolk and white. 1/6th parts of the egg yolk contains proteins, 1/3rd fat and the rest water, Vitamins and minerals like Calcium, Phosphorus, Iron etc.
6. Chalaza
The egg is kept in position at the centre of the egg with the help of the chalaza. It has a thick-cord like appearance and is composed of proteins. This chord-like structure may have to be strained while making custards.

Composition of an Egg

Parts Number Weight H2O Proteins Fats
Whole egg 1 50 Gms 74% 13% 12%
Egg white 1 33 Gms 88% 11% Traces
Egg yolk 1 17 Gms 51% 16% 31%

Selection of Eggs+
Colour
The Colour has no direct effect on the quality of the egg. It depends on the breed, the type of bird and the food consumed. However avoid any eggs with patches formed on the surface as they indicate deterioration of eggs.

Size and Weight
It again depends on the type of bird. An average hen’s egg weighs around 50 gms. The weight should be proportional to the size of the egg. If the size is big and the weight is less, the air cell is big, which indicates that the egg is old.

Egg white
It should not be watery but firm. Firm albumen is a sign of freshness.

Egg yolk
Its colour again depends on the type & feed of the bird. The pigment contained is different feeds are different. Birds that feed on green grass or yellow corn will have a dark yellow colour because of the carotinoids present in the grass. However, avoid eggs which have blood spots (meat spots). The blood spot means that the egg is fertilized and nearing hatching (the blood spots caused by the rupture of a blood vessel during egg formation).
Approximately 1% of all eggs will have these spots which are detected and removed during grading. Electronic blood detectors are sometimes used for grading. Although the blood spot may be objectionable to the consumer, the eggs are chemically and nutritionally fit to eat. In fact, the blood spot is an indicator that the egg is fresh. As the egg ages, the yolk removes H2O from the albumen and dilutes the blood spot.

Free from cracks
The egg must be free from cracks. If the egg is cracked, there are chances that the egg is spoilt, since the micro-organisms have an easy access into the egg.

Flavour and Odour
Generally the eggs don’t have any odour from the outside, except that of the packing material, which must not be strong smelling. Sometimes the smell may penetrate into the egg. Hence, eggs are usually stored away from strong flavoured foods like fish, onions, garlic etc.

In order to maintain the standard, size, quality, colour and weight, the distributors buy eggs, usually from on-farm only, where the diet is kept constant.
If the birds are of the same breed and feed, the standard can be maintained.

Test for freshness
There are two basic tests for judging the freshness of an egg externally i.e. without breaking, as stated under:
1. Water treatment
When egg is placed in water and if it floats, then it is stale. If it sinks completely, it is good. If it floats half-way, then the egg is neither too fresh, nor stale. The air cell increases in size as the eggs get older, which results in floating of eggs.
2. Candling
Egg is placed in a dark room before a candle to see the yolk, white and the presence of blood spots, etc. Now a day, most eggs are graded by passing down on roller over high intensity lights. The eggs are rotated as they move on rollers, so that all parts are visible.

Reasons for storage of eggs
1. As soon as the eggs are laid, they start deteriorating as they come in contact with the atmosphere.
2. The dense albumen becomes thin and watery.
3. Water from the white passes through the yolk; thus lowering its solids as the vitelline membrane is weakened. Chalaza starts to disintegrate and no longer holds the yolk in the centre.
4. If exposed to air, the moisture evaporates and the air cell increases in size.
5. The egg may absorb off-odours, shell being porous.
6. Fresh yolk is slightly acidic, whereas white is alkaline. Loss of carbon dioxide from the egg results in deterioration.

Storage of eggs
Care must be taken in handling and storage of the eggs. They should be stored in their packing trays with the blunt end upwards and the temperature of 7-13°C, at a relative humidity of 70-80%. This way, it can be kept for a month. It should be kept away from onions, garlic, fish etc. Frozen eggs are stored at -18°C. When defrosted, it should be used in the same day.

Dried eggs stay upto one year, if kept unopened in the original container in a cold dry store room. Once opened, it should be used as quickly as possible.

Treating the eggs with oil or wax before refrigeration also extends its shelf life for several months. An odourless, colourless, tasteless mineral oil is used and the process is done under controlled conditions.

Recently, it has been found that small amount of CO2 passed into the storage rooms prevents the loss of CO2 from the eggs, thus enhances the shelf life.
Shelf life of the eggs can be increased by pasteurization at a temperature of 52-55°C for 3 minutes. Thermostabilization is the process in which the eggs are heated in oil or water at about 54-58°C for about 16 minutes to preserve quality during storage. The whites of thermostabilized eggs are more viscous. It is more difficult to separate the white and yolk. More time is required for whipping. It has low foam volume, which leads to decreased volume of the egg products. Other functional properties are not affected.

Cooking of Eggs
The most important rule of egg cookery is “avoid high temperature and long cooking time”. In other words, don’t overcook eggs. Overcooking produces tough eggs, discolouration and it flavour too. Egg white coagulates at 60-65°C, yolk at 65-70°C, whole beaten egg at 69°C and custard at 79-85°C, depending on the amount of milk used. White coagulates before yolk and hence it is possible to boil eggs with firm white and soft yolk. Coagulation depends on length of heating and the presence of added materials like vinegar and salt, which will speed up the coagulation.

Overcooked eggs are tough and rubbery. When eggs are over-cooked, as in case of scrambled eggs and custards, the egg solids separate from liquids or appear curdled. This is known as weeping of eggs.

Blue ring formation on hard-boiled eggs is caused by cooking too long at high temperatures. This is also seen in scrambled eggs, which are cooked on high temperatures. The iron from the yolk combines with the sulphur from the white to form ferrous sulphide, which has blue colour and strong flavour. To avoid blue ring formation, cook at low temperature and arrest the cooking by plunging in cold water or cracking the shell.
Egg white has the ability to trap or hold air – foaming – which helps to increase to seven times its original volume, when beaten. Beaten egg whites give lightness or raising power to fluffy omelets, pudding and soufflés.

Methods of Cooking

Cooking of Egg

In the Shell

Out of the Shell


Soft cooked

Medium cooked
Hard cooked
Unmixed
Mixed

Coddled Egg 1. Poached
2. Fried (Single or Double)
3. Shirred eggs (Baked in individual dishes and served garnished in the same)
4. Cocottes (Eggs steamed in cocotte dishes on a water bath ) 1. Scrambled eggs
2. Omelets (Plain and foamy)

Poaching
The aim is to keep eggs in compact form, rather than spread out over the pan. This is done on a shallow pan because the water is simmering and not boiling, as boiling disintegrates the egg. 5 gms of salt and 10 ml of vinegar for 1 l of water is advisable. Vinegar helps to increase the coagulation, while salt increases the coagulation temperature. Ideal time for poaching is 3-5 minutes.

Frittata
Frittata is a flat omelet that originated in Italy. Flat omelets are made by mixing beaten eggs with a variety of ingredients such as vegetables, meat or cheese and cooking the mixture over low heat without stirring. To finish, it is either flipped over or flashed under the broiler until the top is set.

Soufflés
Soufflés are similar to foamy omelets except that they have a white sauce basis and have some foods such as grated cheese, vegetable pulp or ground meats used for flavour. The heat coagulated protein of both yolk and white give structure to soufflés. The expansion of air in the egg foam as these products bake causes them to rise and appear puffed. Soufflés are baked in special oven-proof moulds at 117°C and served immediately in the moulds in which they are baked. All soufflés - regardless of flavour – should be light, tender, well blended, of good volume, slightly moist and delicately browned.

Factors affecting the whipping quality of eggs
 Season of egg production (Mid-summer eggs beat to lesser volume).
 Quality of egg white (Thick whites give more stable foam).
 Temperature (Eggs at room temperature whip more quickly and to large volume).
 Type of beater (Fine wires divided egg whites easily and air cells remain smaller).
 Container (Bowls with small rounded bottoms and sloping sides are preferable as the beater can more easily be pick up the egg mixture. The size of the bowl depends on the quantity of whites to be whipped).

Effect of added substances
 Milk prevents foam formation due to the presence of fat. Skimmed milk may be used.
 Presence of fat from the yolk, container or beaters may affect the whipping quality.
 Salt decreases the volume and stability of the foam and increases the whipping time.
 Acids decrease the alkalinity and increase the stability of the foam. Acid may be added after the white has started to get stiff foam of good volume.
 Sugar retards denaturation of egg proteins. Add sugar only after the whites are beaten to peaks. Egg white is denatured by beating and heat.

Uses of eggs
 Raising agents as in cakes.
 Binding agents as in koftas and cutlets.
 Flavouring agent (improves taste) as in cakes.
 Emulsifying agent helps in mixing of emulsions.
 Enrichment in child’s feed.
 Rich in nutrients.
 First semi-solid food for infants – as easily digestible.
 Clarifying agent as in consommé.
 Garnishing.