Egg (food)
An
egg is the
ovum produced by a
female animal for
reproduction, often prepared as food.
Most edible eggs, including
bird eggs and
turtle eggs consist of a hard, oval outer eggshell, the "egg white," or
albumen, the
egg yolk, and various thin membranes. Every part of these eggs is edible, although the eggshell is generally discarded.
and
caviar are edible eggs produced by
marine animals.
|
A carton of free-range chicken eggs |
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.
Chicken eggs are widely used in many types of cooking. Dishes that use eggs range from both sweet to savoury dishes. Eggs may 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.
Whole eggs
Many recipes call for whole eggs (without the eggshell).
Common cooking techniques for eggs are:
*
boiling*
poaching*
frying*
bakingSome common egg dishes in
Western cuisine are:
*
boiled eggs*
deviled eggs
*
eggs benedict*
fried eggs
*
omelettes
*
poached eggs
*
scrambled eggs*
soufflé*
quiche*
egg saladSeparated eggs
Eggs are easily separated by cracking the shell and pouring off the egg white while carefully holding the egg yolk in the shell. The egg yolk and the albumen behave quite differently when cooked, so
recipes often require separating the egg white from the yolk.
Yolk
Egg yolks are used to make
mayonnaise and other dishes high in fat. Egg 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.
White
The albumen, or egg white contains protein but little or no fat. It is used in cooking separately from the yolk, and can be aerated or whipped to a light, fluffy consistency known as soft peaks and stiff peaks. Beaten egg whites are used in desserts such as
meringues and
mousse.
Eggshell
Ground egg shells are sometimes used as a food additive to deliver
calcium.
Problems when cooking eggs
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 an abundance of 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.
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.
An egg is surrounded by a thin, hard shell. Inside, the egg yolk is suspended in the egg white by one or two spiral bands of tissue called the
chalazae (from the Greek word
khalaza, meaning hailstone or hard lump.)
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.
White (Albumen)
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 color 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, coloring it. A colorless diet can produce an almost colorless yolk. Farmers may enhance yolk color with artificial pigments, but in most locations, this activity is forbidden.
Abnormalities
|
Three eggs frying, two of which are double-yolked eggs. |
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, these occur more frequently as occasional abnormalities in young hens beginning to lay. Double-yolk eggs are more expensive as they are harder to obtain and contain more nutrition. Usually a double-yolked egg will be longer and thinner than an ordinary single-yolk egg. Double-yolked eggs only rarely, and even then only with human intervention, lead to the successful development of two embryos [
1].
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.
Eggs add
protein to diets, as well as various nutrients.
Chicken eggs are the most commonly eaten eggs, and are highly nutritious. They supply a large amount of complete, high-quality[
2]
protein (which contains all
essential amino acids for humans), 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.
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 (although it has been shown that your body does not absorb much
cholesterol from eggs). 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"[
3] and "The Hearty Egg"[
4]. Nutrition information on the packaging is different for each of the brands.
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.
There is debate over whether egg yolk presents a health risk. Some research suggests it may lower total
Low density lipoprotein ("bad" cholesterol) while raising
High density lipoprotein ("good" cholesterol) levels. Some people advocate the eating of raw eggs and egg yolks for this reason, claiming that uncooked cholesterol in the yolk is healthier than when it is cooked.
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, containers and surfaces that have been used to process raw eggs should not come in contact with ready-to-eat food.
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.
A
USDA study showed that only .003% of eggs produced in the U.S. were shown to contain salmonella, so roughly one in 30,000 eggs produced will contain the bacteria.
Egg shells act as
Hermetic seals which guard against bacteria entering, but this seal can be broken through improper handling or if laid by unhealthy chickens. Most forms of contamination enter through such weaknesses in the shell.
Food allergy
One of the most common
food allergies is eggs. Infants usually have the opportunity to grow out of this allergy during childhood, if exposure is minimized. Generally, physicians will recommend feeding only the yolk to infants because of the higher risk of allergic reaction to the egg white.
Edwina Currie, Salmonella and the UK Lion Mark
The
Lion Mark was introduced to the UK by the
British Egg Information Council (the equivalent of the American Egg Board) in 1998. British Health Minister
Edwina Currie sparked a controversy in 1988 after she issued a warning about salmonella in British eggs that was criticised for being hysterical and over-cautious. The amount of eggs infected by salmonella was a minority and Currie resigned after then UK Prime Minister
Margaret Thatcher stated, "I had eggs for breakfast".
The Lion Mark was launched as an attempt to restore UK public confidence in eggs, which had been smashed by Currie's claims. The Lion Quality Code of Practice includes compulsory vaccination against
Salmonella Enteritidis of all pullets destined for Lion egg-producing flocks, independent auditing improved traceability of eggs and a "best-before" date stamped on the shell and pack which shows that they are fresher than required by law, as well as on-farm and packing station hygiene controls.
Since its introduction in 1998, the Lion Mark has been extremely successful so much so that, in 2001 a UK Government committee (the Advisory Committee on the Microbiological Safety of Food) produced a report highlighting the effectiveness of poultry vaccination in reducing human salmonella cases by half.
This has since been reinforced by the Food Standards Agency which has confirmed the success of the UK egg industry in overcoming salmonella in eggs. In its survey, published in 2004, it tested more than 28,000 UK-produced eggs and no salmonella was found inside any of them.
Approximately 85% of UK eggs are now produced to Lion Quality Standards.
The Lion Mark was itself well known in the UK from the 1950s, which was one reason why it helped to restore public confidence. The British Egg Industry also brought back the popular advertising
strapline from the 1950s,
Go To Work On An Egg.
Chicken eggs are graded by size, for the purpose of sales.
Modern Sizes| Size | Mass | | Very Large (XL) ¦¦ Greater than 73g |
|---|
| Large (L) ¦¦ 63g-73g |
|---|
| Medium (M) ¦¦ 53g-63g |
|---|
| Small (S) ¦¦ less than 53g |
|---|
Traditional Sizes| 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 |
|---|
The most common size of chicken egg is 'Large' and is the egg size commonly referred to for recipes.
Commercial factory farming operations often involve raising the hens in small crowded cages, preventing the chickens from engaging in activities such as wing-flapping, dust-bathing, scratching, pecking, perching and nest-building. Laying hens are often slaughtered 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].
Many
animal welfare advocates object to the
factory farming conditions, such as those stated above, under which laying hens are raised. Animal welfare advocates claim that the resulting frustration and stress on the hens can lead to aggressive behaviour such as feather-pecking and cannibalism.
Free-range eggs are considered by some advocates to be an acceptable substitute to factory 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[
7].
*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 quickly. An already boiled egg will spin into an upright position after a few seconds, but the raw egg will continue to spin on its wide side.
*It is more difficult to break a chicken egg by squeezing it from end-to-end than 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.
*An alternative theory to the floating egg is that because the shell is porous, liquid can slowly evaporate out. Thus an older egg has more evaporated liquid and therefore a bigger air gap. This is used as a test of the freshness of an egg, as a very fresh egg will sink in a bowl of water, and lay on its side. An older egg with a bigger air gap will tilt up slightly, as the air acts as a float. A very old egg will point straight up or may even float to the surface.
*A popular folk remedy for a leaky car radiator is to crack in a raw egg. This has been known to work, as seen on the
Discovery Channel series
MythBusters, 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 demonstrated on
MythBusters, and written about by
Snopes[
8].
*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.
*The world's fastest omelette maker is American
Howard Helmer who rustled up 427 omelettes in 30 minutes in 1990.
*The longest throw of a fresh egg - without breaking it - is 98.51 metres. The record was achieved in Texas, USA in 1978.
*The world's largest omelette was made in Madrid from 5,000 eggs by chef Carlos Fernandez. It weighed 1,320lbs.
*Canada produces the safest eggs of any nation.
*An egg will age more in a 24 hour period at room temperature than it would in an entire week under refrigeration.
*Eggs contain naturally occurring Vitamin D, a rarity with foods.
*Large amounts of salt sprinkled on an egg that has been dropped on the floor aids in faster cleanup.
*It takes a hen 24-26 hours to lay an egg, with the cycle repeating 30 minutes later.
*A large egg contains 75 calories and 5 grams of fat.
*The most expensive egg is a
Fabergé egg called "Winter" which sold for $5.6 million in 1994.
*A typical egg shell contains up to 17,000 pores, through which odors and flavors can pass.
*Keeping eggs stored in their cartons keep eggs fresher by isolating them from the rest of the refrigerator.
*The color of a yolk varies with a hen's diet; although artificial colors are not allowed in chicken feed, naturally occurring items such as yellow-orange marigold petals may be used.
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.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. There is also an element of
humiliation associated with being covered in an egg's contents, referenced by the phrase "egg on one's face".
*
Egg white*
Egg yolk*
Egg timer*
List of egg dishes*
Trophic egg*
Bacon and eggs*
The American Egg Board**
Nutritional values of eggs*
Undercover investigation of animal cruelty in Ohio's largest egg factory*
Criticism of the validity of the "Animal Care Certified" logo used by United Egg Producers(UEP)*
British Egg Industry and the Lion Mark
