Eggs as food
Bird eggs are a common food source. The most commonly used bird eggs are those from the chicken, duck, and goose, but smaller eggs such as quail eggs are occasionally used as a gourmet ingredient, as are the largest bird eggs, from ostriches. The eggs of sea turtles are also sometimes used for food. Eggs are frequently used in both sweet and savoury dishes as a source of protein as well as to bind the other ingredients in a recipe together. Sometimes the egg yolk is used separately from the egg white (or albumen).
The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalaza (from the Greek word khalaza meaning hailstone or hard lump.)
Nutritional value
Chicken eggs are the most commonly eaten eggs, and are highly nutritious. They supply a large amount of complete protein—according to the Food and Agriculture Organization of the United Nations, egg protein is of a higher quality than all other food proteins—and provide significant amounts of several vitamins and minerals, including vitamin A, riboflavin, folic acid, vitamin B6, vitamin B12, choline, iron, calcium, phosphorous and potassium. They are also one of the least expensive single-food sources of complete protein, which is essential to life, health, and well being.
All of the egg's vitamin A, D and E is in the yolk. The egg is one of the few foods which naturally contain vitamin D (although this nutrient is naturally produced in humans when their skin is exposed to sunlight). A large egg yolk contains approximately 60 calories (250 kilojoules); the egg white contains about 15 calories (60 kilojoules). A large yolk contains more than two-thirds of the recommended daily intake of 300 mg of cholesterol. The yolk makes up about 33% of the liquid weight of the egg. It contains all of the fat in the egg and slightly less than half of the protein.
Recently, chicken eggs that are especially high in Omega 3 fatty acids have come on the market. These eggs are made by feeding laying hens a diet containing polyunsaturated fats and kelp meal. Two brands available in the UK are "Columbus Eggs"[1] and "The Hearty Egg"[2]. Nutrition information on the packaging is different for each of the brands.
Health issues of eating chicken eggs
Cholesterol and fat
Chicken egg yolks contain a small amount of fat. People on a low-cholesterol diet may need to cut down on egg consumption, although most of the fat in egg is unsaturated fat and may not be harmful. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little, if any, fat.
Some people try to avoid eggs in their diet because they are high in cholesterol, which is concentrated in the yolk. This issue is sometimes addressed by eating only some or none of the yolk. People sometimes remove the yolk themselves, or may use prepared egg substitutes such as Egg Beaters.
The United States egg industry launched its continuing "Incredible Edible Egg" campaign, which touts eggs as a healthy part of a balanced diet. The American Egg Board publicizes modern research which shows that dietary cholesterol has less effect on blood cholesterol than previously thought.
Contamination
A health issue associated with eggs is contamination by pathogenic bacteria like salmonella. Eggs exit a female bird via the cloaca, so care must be taken to avoid the egg shell becoming contaminated with fecal matter. In commercial practice, eggs are quickly washed with a sanitizing solution within minutes of being laid.
Most health experts advise people to cook their eggs thoroughly before eating them, as the heat is necessary to kill any infectious micro-organisms that may be present. Raw and undercooked eggs have been associated with salmonella infection. As with meat, ready-to-eat food should not come in contact with containers and surfaces that have been used to process raw eggs.
The risk of infection from raw or undercooked eggs is dependent in part upon the sanitary conditions under which the hens are kept. Some smaller egg producers make a point of keeping their hens in cleaner (and, in their view more humane) conditions, and observe few or no cases of salmonella in the birds themselves.
Cooking and preparation
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The primary cooking techniques for eggs are:
Some common egg dishes are
- boiled eggs
- deviled eggs
- eggs benedict
- fried eggs
- omelettes
- poached eggs
- scrambled eggs
- soufflé
- quiche
- egg salad
- century egg
Eggs, particularly their yolks, are important as binding agents in many preparations in European cooking due to the emulsifying action of lecithin. This property is crucial for sauces such as mayonnaise and Hollandaise; custards such as crème anglaise, crème brûlée, flan, and lemon custard; and meat dishes such as sausages and pâté.
Eggs may also be pickled; hard-boiled and refrigerated; or eaten raw, though the latter is not recommended for people who may be susceptible to salmonella, such as the elderly, the infirm, or pregnant women.
If a boiled egg is overcooked, a greenish ring sometimes appears around egg yolk. This is a manifestation of the iron and sulfur compounds in the egg. It can also occur when there is much iron in the cooking water. The green ring does not affect the egg's taste; overcooking, however, harms the quality of the protein.
When eggs become rotten, the yolk will turn green, and the egg will emit a pungent sulfurous odor when broken. Although deemed offensive by most Western palates, fermented eggs are considered a delicacy by some in China when using a special preparation which includes letting them sit for three months to age (or rot, depending on one's interpretation.)
Egg substitutes for baking
For those who choose not to or are unable to consume eggs, alternatives used in baking include other rising agents, such as "Ener-G" egg replacer; or binding materials, such as ground flax seeds. Tofu can also act as a partial binding agent, since it is high in lecithin due to its soy content. Extracted soybean lecithin, in turn, is often used in packaged foods as a cheap substitute for egg-derived lecithin.
Egg characteristics
The shape of an egg is an oval with one end larger than the other end. The egg has cylindrical symmetry along the long axis. The larger end contains the air cell that forms when the contents of the egg cool and contract after it is laid.
Shell
Egg shell color is caused by pigment deposition during egg formation in the oviduct and can vary according to breed, from the more common white and brown to pink or speckled blue-green. Although there is no significant link between shell color and nutritional value, there is often a cultural preference for one color over another. For example, in most regions of the United States, eggs are generally white; while in the northeast of that country and in the United Kingdom, eggs are generally light-brown. These habits may be associated with perceptions of greater purity in white-shelled eggs or greater wholesomeness in brown-shelled eggs.
===Yolk===
The yolk in a newly laid egg is round and firm. As the yolk ages it absorbs water from the albumen which increases its size and causes it to stretch and weaken the vitelline membrane(the clear casing enclosing the yolk). The resulting effect is a flattened and enlarged yolk shape.
Yolk colour is dependent on the diet of the hen; if the diet contains yellow/orange plant pigments known as xanthophylls, then they are deposited in the yolk, colouring it. A colourless diet can produce an almost colourless yolk. Farmers may add natural pigments to enhance yolk colour with artificial colours, but in most locations, this activity is forbidden.
Abnormalities
Some hens will lay double-yolked eggs as the result of unsynchronized production cycles, although heredity causes some hens to have a higher propensity to lay double-yolked eggs. Double-yolked eggs only rarely, and even then only with human intervention, lead to the successful development of two embryos [3].
It is also possible for a young hen to produce an egg with no yolk at all. Yolkless eggs are usually formed about a bit of tissue that is sloughed off the ovary or oviduct. This tissue stimulates the secreting glands of the oviduct and a yolkless egg results.
Issues with mass production
Many animal welfare advocates object to the battery farm conditions under which laying hens are raised. Commercial battery farm operations often involve raising the hens in small crowded cages, preventing the chickens from engaging in normal behavioural activities such as wing-flapping, dust-bathing, scratching, pecking, perching and nest-building. The resulting frustration and stress can lead to aggressive behaviour such as feather-pecking and cannibalism.
Free range eggs are considered by some to be an acceptable substitute to battery farmed eggs. Free range laying hens are given outdoor access instead of being contained in crowded cages. Questions on the actual living conditions of free range hens have been raised as there is no legal definition or regulations for eggs labeled as free range[4].
Laying hens are often slaughterd after twelve months when their egg productivity starts to decline. Some hens may be force molted to increase egg quality and production level after the molting[5].
Due to modern selective breeding, laying hen strains differ from meat production strains. As male birds of the laying strain do not lay eggs and are not suitable for meat production, they are generally killed at one to three days old[6].
Chicken Egg Sizes
Chicken Eggs are graded by size, for the purpose of sales.
| Size | Mass |
|---|---|
| Very Large (XL) | Greater than 73g |
| Large (L) | 63g-73g |
| Medium (M) | 53g-63g |
| Small (S) | less than 53g |
| Size | Mass |
|---|---|
| Size 0 | Greater than 75g |
| Size 1 | 70g-75g |
| Size 2 | 65g-70g |
| Size 3 | 60g-65g |
| Size 4 | 55g-60g |
| Size 5 | 50g-55g |
| Size 6 | 45g-50g |
| Size 7 | less than 45g |
Trivia
- If a raw egg is spun, abruptly stopped and then quickly released, it will start to spin again as the liquid inside continues to rotate. This technique can be used to reliably determine whether an egg is raw or already boiled – a solid egg will remain stationary once halted. Additionally, if a cooked egg and a raw egg are spun with the same force, the cooked egg will spin much faster. Another way of determining if an egg is raw or already boiled is to spin it really fast. An already boiled egg will spin into a upright position after a few seconds, but the raw egg will continue to spin on its wide side.
- It is difficult to break a chicken egg by squeezing it from end-to-end on its long axis.
- An ostrich egg can make omelets for ten people, and takes forty-five minutes of boiling to harden through.
- An egg that floats in water is likely to have been spoiled by bacteria that entered through the pores in the shell and created gas inside it. The increased pressure due to the gas production may push some of the white through the shell, which may also signify a bad egg.
- A popular folk remedy for a leaky car radiator is to crack in a raw egg. This has been known to work, although automotive professionals do not recommend it.
- A popular urban legend holds that an egg can be balanced on its end during equinoxes/soltices, though in reality an egg can just as easily be balanced on any other day. This has been proven on Mythbusters.
- If a raw egg is kept submerged in vinegar (or any acid) for a long enough time (three days for vinegar), the shell will usually dissolve leaving only the inner membrane, which will keep the original shape of the egg. This technique is often used by biologists with Hydrochloric Acid in experiments concerning the permeability of the membrane.
Pop culture
- A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing). Adults often hide the eggs for children to find, an activity known as an Easter egg hunt. See Egg decorating and Easter eggs.
Egg Attacks
Although a food item, eggs are sometimes thrown at people or things such as houses and cars. This act, "egging," is a minor form of vandalism and therefore usually a criminal offence. On Halloween, for example, trick or treaters have been known to throw eggs (and sometimes flour) at property or people from whom they received nothing. Eggs are also often thrown in protests, as they are cheap, nonlethal, and at the same time, very messy when broken.
See also
External links
