Everything you ever wanted to know about Eggs

by Jennifer Behm – Chicken farmerLast Updated– 17 January 2021

For most people, the primary reason for keeping chickens is to have a constant supply of fresh organic eggs. But there is a lot more to an egg than meets the eye. So in this section, we will try to provide you with everything you ever wanted to know about eggs and more.

Read on:

The Anatomy of an Egg

chicken egg anatomy


The diagram identifies the different parts of an egg

The egg protects and provides a complete diet for the developing embryo and serves as the principal source of food for the first few days of the chick’s life. Egg is also one of the most nutritious and versatile of human foods.

When the egg is freshly laid, the shell is completely filled. The air cell is formed by contraction of the contents during cooling and by the loss of moisture. A high-quality egg has only a small air cell.

The yolk is well-centered in the albumen and is surrounded by the vitelline membrane, which is colourless. The germinal disc, where fertilization takes place, is attached to the yolk. On opposite sides of the yolk are two, twisted, whitish cord-like objects known as chalazae. Their function is to support the yolk in the centre of the albumen. Chalazae may vary in size and density, but do not affect either cooking performance or nutritional value.

A large portion of the albumen is thick. Surrounding the albumens are two shell membranes and the shell itself. The shell contains several thousand pores that permit the egg to ‘breathe’.


An average-sized egg weighs approximately 57 grams (about 2 ounces). Of this weight, the shell constitutes 11 percent; the white, 58 percent; and the yolk, 31 percent. Normally, these proportions do not vary appreciably for small or large eggs. The percentage composition of the edible portions is:

Percent Water Protein Fat Ash
Whole egg 74 13 11 1
White 88 11 .. ..
Yolk 48 17 33 1

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Essential nutrients

Eggs are especially valuable as a economic source of protein and contain about 6 to 7 grams of protein. People of all ages need adequate protein for building and repairing body tissues. The fat in the yolk is so finely emulsified that it is digested easily, even by infants. The ratio of unsaturated to saturated fats is about 2 to 1, which is considered very desirable. Oleic acid is the main unsaturated fat and it has no effect on blood cholesterol. Eggs contain vitamin A, the B vitamins (thiamin, riboflavin, and niacin), and vitamin D, all of which are necessary during childhood and adolescence for growth. Eggs also contain an abundant supply of minerals, such as iron and phosphorus, that are essential for building and maintaining strong, healthy bodies. But eggs are low in calcium (it is in the shell), and contain little or no vitamin C.

Individuals on weight-reducing programs find eggs beneficial as an egg provides good nutrition and contains only about 80 calories.

Egg Yolks, Egg White and Egg Shell Problems and Variations

egg yolks white shell

If your birds are happy and healthy then you should have very little problems and they will deliver perfect eggs day after day. However as a chicken keeper there are several variations that you should be aware of and recognise .

Most of these variations in eggs are nothing to worry about, however, some may mean that your birds are missing some essential nutrients or are suffering from parasites or other health issues and need to be treated accordingly.

Pale Egg Yolks

It is natural for yolks to become paler when the grass and other greenery such as clover is not growing. Consumers are known to prefer deeper coloured yolks and tend to have the erroneous perception that such eggs show that the birds have had a  more, free-range and natural life. Unfortunately battery egg producers often give their birds feed that contains artificial colouring agents to make the yolks a deeper colour. However pale yolks can also be a sign of ill-health.

Greenish Yolk Colour

Occasionally free range chickens will produce eggs with green yolks, this occurs most frequently in the spring when plants are most succulent . The problem should be rectified by reducing the amount of greens in the bird’s diet and increasing the amount of compound feed.

Double Egg Yolks

Double egg yolks or double yolks are a rare treat if you like egg yolks. It is estimated that there is only a 1 in a 1000 chance of finding a double yolk egg in commercial eggs and what are the chances of finding a nine yolker, which is the current record.

If you rear your own chickens you will come across a double yolk egg more often as they tend to be laid by young birds, especially if they belong to a high egg-producing breed. Often young birds will produce double egg yolks when they are just starting to lay and their egg production system is just getting going, this becomes less frequent and usually stops altogether as their reproductive systems settle down. However, stress can also cause older birds to lay double yolk eggs.

A double yolk occurs when two yolks are released into the oviduct (ovulation) at the same time and are then encased by one shell. If things are functioning properly this would not happen as the action of laying the egg is what triggers the next yolk sac to be released.

Nature does not allow for twin poultry as an egg just does not have space for more than one chick, so even if they are fertilized no chicks will be produced. This means that any breeds predisposed to double yolk production are less likely to survive as their reproductive success is impaired.

Wind egg

This is a small egg with no yolk and it is fairly common when a pullet is first coming into lay. It is not important and can be ignored, unless the pullet continues to lay such eggs. Wind eggs can also occur in older hens if they are subjected to a sudden shock.

Egg with blood spots inside the yolk

These are small red to reddish-brown spots found in or around the yolk. They are usually caused by one of the tiny blood vessels in the ovary breaking at the time when the yolk is released. Often people mistakenly think they indicate a fertile egg and it is the start of a chick forming. Stress or a lot of disturbance, particularly at the time of ovulation is likely to increase the incidence of these blood spots. Because free range hens can usually eat grass which contains a substance called rutin, which helps stop bleeding, free range hens eggs tend to have less blood spots than those from caged or battery kept birds.

Egg with blood (meat spots) spots inside the white

These are usually a more browner colour than blood spots in yolks and consist of  small pieces of body tissue, such as the internal wall of the oviduct. This often occurs in older birds or again as a result of stress. However there is some evidence that there is a hereditary tendency to this condition, so it may be advisable to avoid breeding from such a hen.

Egg with blood on the shell

This is often the result of straining on the part of the hen especially where large eggs are involved. It may also be more prevalent in a pullet first coming into lay. If the shells have small spots of blood on them, rather than streaks, then this could be a sign that you have a red mite problem and you need to take appropriate action quickly.

Dark egg shells becoming pale

Shells that are normally dark brown may become lighter for a number of reasons, including stress, illness or lack of the correct food. The main reason, however, is the hen being exposed to strong sunlight on her back for long periods. To avoid this always ensure that the birds have enough shaded areas.

Dirty eggs

Nest box material needs to be checked frequently and soiled material removed. Also ensure that eggs are collected frequently. You should also check the bird’s vent to ensure that there is no mess around this area, which could indicate a health problem.

Watery Whites or Albumen

Although eggs are usually safe to eat for around 28 days as long as they are kept in a cool environment, they do start to deteriorate from the day that they are laid. Newer eggs have firm whites that hold their shape and poor quality whites usually indicates that the egg is getting to the end of, or is passed its shelf  life. However some newly laid eggs from older birds may also have poor quality whites. In addition in younger birds it can be an indication that the bird is suffering from a viral condition.

Middle-banded egg

A sudden shock can cause a temporary interruption in the egg-formation system. If there is an egg being formed at the time of the shock, it may end up with an extra band or ridge around it. This is normally nothing to worry about, as long as the flock is not subjected to regular trauma.

Misshapen eggs

These differ from middle-banded eggs in having a range of distortions, including soft ends and uneven or ribbed surfaces. Thin patches or excessively chalky areas may also be seen. Misshapen eggs are more common with older hens, but may also indicate a disease such as Infectious bronchitis or Egg drop syndrome. If the condition persists, you should seek professional advice.

Bubbles in the Egg White

Eggs normally have an air space at the blunt end and the shell is permeable to the air to allow oxygen in to the developing chick. However if the inner membrane is damaged the result can be bubbles in the egg white.

Rotten Eggs

Usually, the shell membranes that lie just under the shell protect the egg from microbial and fungal infection. If this layer is damaged or malformed and infections get into the egg, rot in patches or throughout will occur. This is usually accompanied by a pungent smell.

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Know your egg labels

Eggs in their containers

It used to be eggs were either small or large, brown or white. Now there is a plethora of terms out there to describe eggs. When buying eggs now it is important to know what some of these terms really mean as a lot of them refer to the conditions in which the hens that laid the eggs are kept. It is all to easy to be fooled into believing you are buying eggs from hens that have a healthy and happy life, when in actual fact they are little better than battery hens.

Here are some of the terms you will come across on egg labels:

Standard eggs

Standard eggs, otherwise known as regular eggs, commercially produced eggs, conventional eggs, battery farm eggs or just eggs are unfortunately the most common type of eggs to be found in our supermarkets and shops. The chickens are kept in small cages, anything between 3 – 7 hens per cage, so there is not enough room for the hens to stretch or scratch.  Each hen is allotted a space smaller than a single sheet of paper and must stand on a sloped wire floor, to allow easy egg collection, that causes discomfort and often serious injury.

Thousands of these cages are found in large artificially lit sheds that can contain from around 20,000 – 100,000 birds altogether. The hens are fed a high protein diet containing antibiotics, hormones and other chemicals.

Obviously, due to a high output and minimum care for the birds, the cost of this type of egg is low and therefore standard eggs are the cheapest eggs that you can buy in the shops. This is all well and good for the consumer, but the hens suffer considerably and  any decent minded person would want these to be banned.

Given the poor conditions these birds are kept in and the chemical cocktail they are fed unsurprisingly the nutritional value of these eggs is less than eggs from chickens kept in more humane conditions. In most developed countries over 90% of eggs are produced in this inhumane way. 

Farm Fresh Eggs

The term conjures up a lovely rural scene, but the reality is not lovely. The farm in this context, means a huge pre-fabricated shed, an industrial unit. Fresh means less than 21 days old, not what I would call fresh!

Do not be fooled this is just another name for standard eggs (UK equivalent) above and the poor chickens spend their lives in inhumane cages.

Barn-laid eggs

These eggs are produced by hens that are kept indoors, albeit in large barns covered with straw and separated into pens rather than into small cages. The hens have much more room to move around and are able to carry out their natural activities, such as spreading their wings, scratching for food and even socialising with other hens. This method of egg farming has been approved by the RSPCA and is considered a much more humane way to keep hens. 

Free Range Eggs

This is not as good as people think unfortunately once again we’re talking about an industrial unit type house but, they do have access to a fenced off area outside. Although the stocking density is limited to 2,500 birds per hectare (that’s about 64 sheets of A4 paper per hen) most birds will hang around the shed if they do go out.

As hens tend to stick together the area around the shed gets pretty grim, it is stripped of vegetation and either a dustbowl or a muddy mess depending upon the time of year. Free-range hens can at least stretch and move around but the sheer numbers and their nature mean they do not take advantage of their better conditions.

Organic eggs

Organic eggs come from hens that have outdoor access during the day and are able to run around outside in an area covered with natural vegetation. They are fed a wholly organic grain feed, which has been organically grown and therefore must not contain any pesticides, herbicides or fertilizers. The birds are raised healthily, in a healthy environment and are fed only natural ingredients. They are not given any antibiotics, hormones or meat by-products to fatten them up or make them grow bigger. These are the type of eggs your own chickens will provide you with.

Most people immediately notice a difference in the taste of organic eggs. Although organic eggs are more expensive than regular eggs, at least you know what you are putting into your body and that the hen that laid the eggs has been well cared for.

Vegetarian eggs

This type of eggs is produced by hens that are only fed a vegetarian diet and thereby do not consume any meat or fish products. In order to ensure they have a strict diet they have to be kept in cages and therefore are not classed as ‘free-range’.

Omega-3 eggs

Hens that produce omega-3 enhanced eggs are fed a special vegetarian diet that consists of canola, linseed and flax seed. These products are all rich in omega-3 essential fatty acids, which means that the eggs produced all contain higher levels of omega-3 fatty acids than other types of eggs.

Omega-3 fatty acids are primarily found in oily fish and therefore most people do not consume adequate levels of this beneficial fatty acid. Although this type of egg is healthier, the hens that lay the eggs to control their diets have to be kept in unhealthy conditions, in battery cages.

Vitamin enhanced eggs

Hens are fed extra amounts of certain vitamins such as vitamins E, B6, and B12, to enhance the amounts of these vitamins contained in their egg.


When buying eggs, organic eggs are best, a free-range second followed by barn eggs. If we all voted with our wallets then we really could do something to help these poor caged birds. The best way to ensure that you only use eggs that have been produced by happy healthy chickens is to raise your own hens. Failing that try to buy from a farm where you can check out the hens laying conditions before you purchase the eggs. 

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