Theory of eggs

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Theory of eggs

Egg whites, egg yolks, whisked eggs, aged ones or everything you wanted to know about eggs!

 

 

Over 40 billions of eggs were produced in Russia during one year. An average Russian citizen eats about 270 eggs per year. Almost every our recipe includes eggs but we don’t usually think of the role they play in cooking. Let’s sort everything out.

The anatomy of an egg

An egg consists of 6 parts:

  1. thin albumen,
  2. thick albumen,
  3. egg yolk,
  4. eggshell,
  5. air cell,
  6. and chalaza (serves to keep the yolk centered).

⅔ of an egg is represented by an egg white and ⅓ – by an egg yolk. As an egg white consists of 90% water, most part of an egg is liquid which contains a lttle albumen, fat and emulsifiers.

Emulsifiers are substances which help to create emulsions from immiscible liquids.

Let’s try to figure everything out and have a closer look at egg parts.

Egg white

Another name of an egg white is albumen. An egg white consists of protein and water (10% of protein and 90 % of water), and it contains no fats. Unlike a yolk an egg white has little flavour or colour.

Egg yolk

Yolks contain 50% of liquid and 50% of solid substances. As eggs age, yolks pick up additional moisture from the whites. When it happens yolks become thinner and spread out if pouring onto smooth surface. Yolks have protective membranes that weaken as they age making it more difficult to separate an egg yolk from an egg white. If eggs are not stored in cool place the weakening of a membrane increases the possibility of bacteria penetration and reproduction in egg yolks high in healthy components.

Eggshell

An eggshell comprises 10% of total egg weight. Even though it serves as a protective membrane it is very porous. It means that odours can enter an eggshell, and an egg can lose moisture and gases. An eggshell is usually washed and covered with a special liquid in order to kill salmonella. It can also be treated with a mineral oil to avoid evaporation from the egg. Eggshell contains water, organic substances and about 95% of inorganic compounds, i.e. mostly calcium carbonate.

Salmonellae are rod-shaped bacteria. Some species of salmonellae are not dangerous to humans but some are agents of typhoid fever and other salmonelloses.

The colour of an eggshell doesn’t impact flavour. Nutritional value and functions of eggs depend only on chicken breeds.

Air cell

Eggs have 2 protective membranes between an eggshell and an egg white. Soon after an egg has been laid an air cell starts to form in a large rounded end of an egg. As an egg ages it loses moisture and an air cell increases. That is why old eggs float and fresh eggs sink.

Chalaza (cords)

Chalazae are twisted cords in an egg white which serve to keep the yolk centered. If you can see it in the egg it means that the egg is fresh. Many chefs strain eggs to remove chalazae although it doesn’t influence baking.

Shell membranes

Inner and outer shell membranes surround albumen in order to provide a protective barrier against bacterial penetration. An air cell is created between these membranes.

Germinal disk

On the yolk surface you can observe apparent density – it is a developing embryo.

Egg grade and size


In the sorting process eggs are examined for both interior and exterior quality, and for weight. Grade and size of the eggs are two different notions.

Ранг и размер яиц

The USA

In the USA in the descending order of quality, grades are usually designated: AA, A and B. Nutritional values of different grades are the same.
 

Grade AA

 
An air cell occupies little space, albumen is thick, chalaza is prominent. Yolk is thick, round and high. Shell is of usual shape, clean. Such eggs are good for all purposes: frying, boiling.
 
 

Grade A

 
An air cell occupies a little space, albumen is thick, chalaza is prominent. Yolk is thick, round and slightly high. Shell is the same as grade AA eggs have. They are used for the same purposes.
 
 

Grade B

 
An air cell occupies a lot of space, there is no much thick albumen, chalaza isn’t prominent or invisible, a yolk is flattened and enlarged. The shell is misshapen with small defects. Such eggs are good for scrambled eggs and baking but it can be hard to whisk such egg whites as they contain too much water.
 
 

U.S. egg sizes are divided into 6 categories by weight:

  • Jumbo – about 72 g per egg
  • Extra large – about 64 g per egg
  • Large – about 57 g per egg
  • Medium – about 50 g per egg
  • Small – about 43 g per egg
  • Peewee – about 35 g per egg

Canada

There only 2 egg grades in Canada: A and B. Even though egg grades don’t indicate egg age egg quality depends on time intervals. Even if you store AA eggs in the refrigerator for 1 week they become A grade. In 5 weeks they become B grade as albumen becomes thin and an air cell increases. Nevertheless good storage conditions allow to preserve nutritional values.

Russia, Belarus

Depending on the storage life, quality and weight chicken eggs are divided into diet and table eggs in Belarus and Russia: D and C.

Diet eggs (D) – eggs which are not stored at low temperature and are sold during 7 days after being laid excluding the day of laying. Every egg is marked with a red stamp on its eggshell which specifies a date of laying and an egg category.

Table eggs (C) – eggs which storage life doesn’t exceed 25 days starting from the sorting day but excluding the day of laying, and eggs stored at a low temperature no more than 120 days with an air cell height no more than 7 mm, stored at a low temperature – no more than 9 mm. Every egg is marked with a blue stamp on its eggshell which specifies an egg category only based on an egg weight. Sometimes it is allowed not to mark table eggs.

A second part of a stamp (a number) indicates the weight of an egg.

  • Category 3 (3): the smallest eggs, their weight vary from 35 to 44.9 g.
  • Category 2 (2): weight vary from 45 to 54.9 g.
  • Category 1 (1): large eggs, their weight vary from 55 to 64.9 g.
  • Hand picked eggs (O): the largest eggs, their weight vary from 65 g to 74.9 g.

You can also find eggs the weight of which exceeds 75 g – such giants are adjudged to the highest category (B).

And let me repeat it once again: brown eggs differ from white eggs only in the shell colour. There is absolutely no difference between them. Different chicken breeds lay eggs of different shell colour (Brown eggs are laid by chickens of Asian breeds).

Chemical analysis of eggs with different shell colours hasn’t identified any differences in their health value or flavour. Eggshell colour doesn’t have any impact on its nutritional value.

Egg products


The term “egg products” refers to eggs removed from their shells and sold in stores: egg yolks, egg whites, whole eggs. Egg products vary form refrigerated and frozen to powdered ones. According to the law egg products must be pasteurised that is why they don’t contain salmonellae, i.e. they are safe to use in a raw condition.

Egg products

Pasteurisation is a process that kills pathogenic bacteria, micro organisms such as salmonellae in food.

Eggs can not be pasteurised at high temperature because protein starts coagulating.

Coagulation is also known as clotting.

Standard egg pasteurization includes heating of an egg for 3.5 minutes at 60°C. Other methods include holding of powdered whites at 54°C for 7 days. Pasteurisation doesn’t impact egg qualities.

Advantages of egg products


  • safety, as they are pasteurised
  • save time (don’t have to crack eggs)
  • low price
  • minimum room for storage, no losses when cracking eggs
  • long-term storage life
  • no need in separation of whites from yolks
  • the same egg quality as eggs with eggshells have.

Types of egg products


Frozen egg whites

They often contain guar gum which serves as a thickener. Guar gum protects egg whites from the harmful effect of ice crystals. Guar gum also improves thickness and an ability of frozen egg whites to create foam. Such agents as triethyl citrate or sodium laureth sulfate which serve as aid for whipping egg whites are often added to frozen egg whites. That is why frozen egg whites are whisked faster than usual egg whites. They are used for all purposes.

 

Frozen sugar yolks

Frozen egg yolks contain about 10% of sugar or glucose syrup. Addition of sweetener lowers freezing point preventing egg yolks from the harmful effect of ice crystals. It can have an impact on yolk characteristics – thicker yolks won’t form an emulsion.

If you substitute fresh yolks with frozen sugar yolks you should be more careful with the amount of sugar you add to the dish.

When substituting 1 kg of fresh yolks you have to take 1.1 kg of frozen sugar yolks. But don’t forget to take 100 g of sugar less.

 

Refrigerated yolks

They don’t contain additional agents. They are usually used for sauces, where it’s important to create emulsions.

Want to know more about agents? Please proceed with our next lesson “Coagulants”.

 

Frozen whole eggs

Frozen whole eggs often contain a small amount of citric acid which prevents eggs from becoming grey when they are being heated.

Frozen whole eggs

 

Liquid egg products

Egg beaters contain 99% of egg white which doesn’t contain fat. They often contain carotenoids as a yellow colourant. They can also contain vitamins, minerals, milk protein, gums.

 

Powdered eggs

Yolks, whites and whole eggs are dried until humidity reaches 5%. They are used for the cooking of muffins, biscuits and some cakes. Some chefs add egg white powder to liquid egg white to increase the volume and the stability of the meringue.

 

The functions of eggs


Main functions


Structure

Coagulated albumin proteins (in egg whites and yolks) are important to add structure to baked products. Cakes can collapse without eggs. Coagulated proteins provide thickness and gelation (as a texture variety) of pastry creams, creme Anglaise, custards. Eggs are unique because they contain both thickeners (proteins) and softeners (fats and emulsifiers).

 

Aeration

Eggs can form stable foam and by doing so they provide aeration. Foam consists of small bubbles of air or some other gas, surrounded by liquid or solid film. With the help of aeration eggs help the process of leavening. True leavening agent is air. Eggs form foam which helps air to “enter” baked products.

Aeration

 

Emulsification

Yolks are good emulsifiers which prevent fats and water from separating. Eggs are often added to cream butter or shortening to emulsify and stabilise the mixture.

 

Flavour

Egg yolks give full-bodied flavour to the dish as fat is concentrated in them.

 

Colour

Yolks containing yellow-orange carotenoids add yellow colour to the baked products, creams and sauces. Eggs contain proteins which participate in Maillard reaction and add yellowish colour to pastry.

Colour

 

Nutritional value

Egg whites and yolks have high nutritional value. Eggs contain vitamins and minerals. Carotenoids act as antioxidants and play an important role in our health.

Additional functions


Prevention form staling

Egg fats, emulsifiers and proteins prevent starch from retrogradation which is a cause of product staling.

Starch retrogradation is a standard process of rearrangement of dissolved polysaccharides into their undissolved form as a result of cooling and storage of products. Retrogradation has a detrimental effect on food quality. Starch gel loses its elasticity, becomes thicker, solid; we can observe the separation of moisture. It usually leads to staling of bakery products, and to the separation of moisture in porridges and jellies.

 

Glossy finish of the baked products

Egg proteins give glossy golden brown finish to the dish if products are covered with eggs or the mixture of eggs and milk.

 

Binding agent

Eggs act as a binding agent that holds nuts, spices and sugar together. Eggs enables liquid batter to stick to the surface a product during frying (batter).

Binding agent

 

Silky texture of sweets and frozen deserts

Fats, emulsifiers and proteins prevent crystallisation and provide smooth, silky texture of sweets and frozen deserts.

 

Moisture

Whole eggs contain 75% of liquid. As soon as eggs are added to the batter it becomes moist too.

Moisture

 

Increase in the softness of batter

Eggs compete with gluten formation in batter. Fats and emulsifiers interact with bonds within gluten filaments and weaken them.


 

Meringue and its kinds →

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