Egg (food)
From Wikipedia, the free encyclopedia
Eggs are laid by female animals of many different species, including
birds,
reptiles,
amphibians, and
fish, and have been eaten by humans for thousands of years. Bird and reptile
eggs consist of a protective
eggshell, albumen (
egg white), and vitellus (
egg yolk), contained within various thin membranes. Popular choices for egg consumption are
chicken,
duck,
quail,
roe, and
caviar, but the egg most often consumed by humans is the chicken egg, by a wide margin.
Egg yolks and whole eggs store significant amounts of
protein and
choline, and are widely used in cookery. Due to their protein content, the
United States Department of Agriculture categorizes eggs as
Meats within the
Food Guide Pyramid.
Despite the nutritional value of eggs, there are some potential health
issues arising from egg quality, storage, and individual allergies.
Chickens and other egg-laying creatures are widely kept throughout
the world, and mass production of chicken eggs is a global industry. In
2009, an estimated 62.1 million metric tons of eggs were produced
worldwide from a total laying flock of approximately 6.4 billion hens.
There are issues of regional variation in demand and expectation, as
well as current debates concerning methods of mass production. The
European Union recently banned
battery husbandry of chickens.
History
Bird eggs have been valuable foodstuffs since
prehistory,
in both hunting societies and more recent cultures where birds were
domesticated. The chicken was probably domesticated for its eggs from
jungle fowl native to tropical and subtropical Southeast Asia and India
before 7500
BCE. Chickens were brought to Sumer and Egypt by 1500 BCE, and arrived in Greece around 800 BCE, where the
quail had been the primary source of eggs.
In
Thebes, Egypt,
the tomb of Haremhab, built about 1420 BCE, shows a depiction of a man
carrying bowls of ostrich eggs and other large eggs, presumably those of
the
pelican, as offerings.
In
ancient Rome, eggs were preserved using a number of methods, and meals often started with an egg course. The
Romans crushed the shells in their plates to prevent evil spirits from hiding there.
In the
Middle Ages, eggs were forbidden during
Lent because of their richness. The word
mayonnaise possibly was derived from
moyeu, the medieval French word for the yolk, meaning center or hub.
Egg scrambled with acidic fruit juices were popular in
France in the 17th century; this may have been the origin of
lemon curd.
The dried egg industry developed in the 19th century, before the rise of the frozen egg industry. In 1878, a company in
St. Louis, Missouri started to transform egg yolk and white into a light-brown, meal-like substance by using a drying process. The production of dried eggs significantly expanded during
World War II, for use by the United States Armed Forces and its allies.
In 1911, the
egg carton was invented by Joseph Coyle in
Smithers, British Columbia, to solve a dispute about broken eggs between a farmer in
Bulkley Valley and the owner of the Aldermere Hotel. Early egg cartons were made of paper.
Varieties
Quail eggs (upper left), chicken egg (lower left) and
ostrich egg (right)
Bird eggs are a common
food and one of the most versatile
ingredients used in cooking. They are important in many branches of the modern
food industry. The most commonly used bird eggs are those from the
chicken.
Duck and
goose eggs, and smaller eggs, such as
quail eggs, are occasionally used as a gourmet ingredient, as are the largest bird eggs, from
ostriches.
Gull eggs are considered a delicacy in
England, as well as in some Scandinavian countries, particularly in
Norway. In some African countries,
guineafowl eggs are commonly seen in marketplaces, especially in the spring of each year.
Pheasant eggs and
emu eggs are perfectly edible, but less widely available.
Sometimes they are obtainable from farmers, poulterers, or luxury
grocery stores. Most wild birds’ eggs are protected by laws in many
countries, which prohibit collecting or selling them, or permit these
only during specific periods of the year.
See also
fish eggs.
Anatomy and characteristics
A raw chicken egg within its membrane, the shell removed by soaking in vinegar
The shape of an egg resembles a
prolate spheroid with one end larger than the other, with cylindrical symmetry along the long axis.
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 χάλαζα, meaning hailstone or hard lump).
Air cell
The larger end of the egg contains the air cell that forms when the
contents of the egg cool down and contract after it is laid. Chicken
eggs are graded according to the size of this air cell, measured during
candling.
A very fresh egg has a small air cell and receives a grade of AA. As
the size of the air cell increases, and the quality of the egg
decreases, the grade moves from AA to A to B. This provides a way of
testing the age of an egg: as the air cell increases in size,
the egg becomes less dense and the larger end of the egg will rise to
increasingly shallower depths when the egg is placed in a bowl of water.
A very old egg will actually float in the water and should not be
eaten.
Shell
Egg shell color is caused by
pigment deposition during egg formation in the
oviduct and can vary according to
species and
breed, from the more common white or brown to pink or speckled blue-green. In general,
chicken breeds with white ear lobes lay white eggs, whereas chickens with red ear lobes lay brown eggs.
Although there is no significant link between shell color and
nutritional value, there is often a cultural preference for one color
over another (see 'Color of eggshell', below).
White
White is the common name for the clear liquid (also called the
albumen or the glair/glaire) contained within an egg. In chickens it is
formed from the layers of secretions of the anterior section of the
hen's
oviduct during the passage of the egg. It forms around either
fertilized
or unfertilized yolks. The primary natural purpose of egg white is to
protect the yolk and provide additional nutrition for the growth of the
embryo.
Egg white consists primarily of about 90% water into which is dissolved 10%
proteins (including
albumins,
mucoproteins, and
globulins). Unlike the yolk, which is high in
lipids (fats), egg white contains almost no fat, and the
carbohydrate content is less than 1%. Egg white has many uses in food, and many others, including the preparation of
vaccines such as
those for influenza.
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.
Lutein is the most abundant pigment in egg yolk.
A colorless diet can produce an almost colorless yolk. Yolk color is,
for example, enhanced if the diet includes products such as yellow
corn and
marigold petals. In the US, the use of artificial color additives is forbidden.
Abnormalities
See Double-yolk eggs and Yolkless eggs.
Culinary properties
Types of dishes
A fried chicken egg, "sunny side up"
Chicken eggs are widely used in many types of dishes, both sweet and savory, including many
baked goods. Some of the most common preparation methods include
scrambled,
fried,
hard-boiled, soft-boiled,
omelettes and
pickled. They can also be eaten raw, though this is not recommended for people who may be especially susceptible to
salmonellosis,
such as the elderly, the infirm, or pregnant women. In addition, the
protein in raw eggs is only 51% bioavailable, whereas that of a cooked
egg is nearer 91% bioavailable, meaning the protein of cooked eggs is
nearly twice as absorbable as the protein from raw eggs.
As an ingredient, egg yolks are an important
emulsifier in the kitchen, and are also used as a thickener in
custards.
Soft-boiled quail eggs, with potato galettes
The
albumen, or egg white, contains protein, but little or no
fat,
and can be used in cooking separately from the yolk. The proteins in
egg white allow it to form foams and aerated dishes. Egg whites may be
aerated or whipped to a light, fluffy consistency, and are often used in
desserts such as
meringues and
mousse.
Ground egg shells are sometimes used as a
food additive to deliver
calcium.
Every part of an egg is edible,
although the eggshell is generally discarded. Some recipes call for
immature or unlaid eggs, which are harvested after the hen is
slaughtered or cooked while still inside the chicken.
Cooking
Eggs contain multiple proteins which gel at different temperatures
within the yolk and the white, and the temperature determines the
gelling time. Egg yolk begins to
gelify,
or solidify, when it reaches temperatures between about 63 and 70 °C
(145 and 158 °F). Egg white gels at slightly higher temperatures, about
60 to 80 °C (140 to 176 °F)- the white contains
ovalbumin
that sets at the highest temperature. However, in practice, in many
cooking processes the white gels first because it is exposed to higher
temperatures for longer.
Salmonella is killed instantly at 71 °C (160 °F), but is also killed
from 54.5 °C (130.1 °F) if held there for sufficiently long time
periods.
To avoid the issue of salmonella,
eggs can be pasteurised
in-shell at 57 °C (135 °F) for an hour and 15 minutes. Although the
white is slightly milkier, the eggs can be used in normal ways. Whipping
for meringue takes significantly longer, but the final volume is
virtually the same.
If a boiled egg is overcooked, a greenish ring sometimes appears around egg yolk due to the
iron and
sulfur compounds in the egg. It can also occur with 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.
Chilling the egg for a few minutes in cold water until it is completely
cooled may prevent the greenish ring from forming on the surface of the
yolk.
Flavor variations
A batch of
tea eggs with shell still on soaking in a brew of spices and tea
Although the age of the egg and the conditions of its storage have a
greater influence, the bird's diet does affect the flavor of the egg. For example, when a brown-egg chicken breed eats
rapeseed or soy meals, its intestinal microbes metabolize them into fishy-smelling
triethylamine, which ends up in the egg. The unpredictable diet of free-range hens will produce unpredictable eggs. Duck eggs tend to have a flavor distinct from, but still resembling, chicken eggs.
Eggs can also be soaked in mixtures to absorb flavor.
Tea eggs are steeped in a brew from a mixture of various spices, soy sauce, and black tea leaves to give flavor.
Storage
Careful storage of edible eggs is extremely important, as an improperly handled egg can contain elevated levels of
Salmonella bacteria that can cause severe
food poisoning. In the US, eggs are washed, and this cleans the shell, but erodes the cuticle. The USDA thus recommends refrigerating eggs to prevent the growth of
Salmonella.
Refrigeration also preserves the taste and texture. However,
uncracked eggs can be left unrefrigerated for several months without
spoiling.
In Europe, eggs are not usually washed, and the shells are dirtier,
however the cuticle is undamaged, and they do not require refrigeration. In the UK in particular, hens are immunised against salmonella, and the eggs are generally safe for 21 days.
Preservation
The simplest method to preserve an egg is to treat it with
salt. Salt draws water out of
bacteria and
molds, which prevents their growth.
The Chinese
salted duck egg is made by immersing duck eggs in
brine, or coating them individually with a paste of salt and
mud or
clay. The eggs stop absorbing salt after about a month, having reached osmotic equilibrium.
Their yolks take on an orange-red color and solidify, but the white
remains liquid. They are boiled before consumption, and are often served
with rice
congee.
Pickled egg, colored with beetroot juice
Another method is to make
pickled eggs, by boiling them first and immersing them in a mixture of
vinegar, salt, and spices, such as
ginger or
allspice. Frequently,
beetroot juice is added to impart a red color to the eggs.
If the eggs are immersed in it for a few hours, the distinct red,
white, and yellow colors can be seen when the eggs are sliced.
If marinated for several days or more, the red color will reach the yolk. If the eggs are marinated in the mixture for several weeks or more, the vinegar will dissolve much of the shell's
calcium carbonate and penetrate the egg, making it
acidic enough to inhibit the growth of bacteria and molds.
Pickled eggs made this way will generally keep for a year or more without refrigeration.
A
century egg or hundred-year-old egg is preserved by coating an egg in a mixture of
clay,
wood ash, salt,
lime, and
rice
straw for several weeks to several months, depending on the method of
processing. After the process is completed, the yolk becomes a dark
green, cream-like substance with a strong odor of sulfur and ammonia,
while the white becomes a dark brown, transparent jelly with a
comparatively mild, distinct flavor. The transforming agent in a century
egg is its
alkaline material, which gradually raises the
pH of the egg from around 9 to 12 or more.
This chemical process breaks down some of the complex, flavorless
proteins and fats of the yolk into simpler, flavorful ones, which in
some way may be thought of as an "inorganic" version of
fermentation.
Cooking substitutes
For those who do not consume eggs, alternatives used in baking include other rising agents or binding materials, such as ground
flax seeds or
potato starch flour.
Tofu can also act as a partial binding agent, since it is high in lecithin due to its
soy content.
Applesauce can be used, as well as
arrowroot and
banana. Extracted
soybean lecithin, in turn, is often used in packaged foods as an inexpensive substitute for egg-derived lecithin.
Other egg substitutes are made from just the white of the egg for
those who worry about the high cholesterol and fat content in eggs.
These products usually have added vitamins and minerals, as well as
vegetable-based emulsifiers and thickeners such as
xanthan gum or
guar gum. These allow the product to maintain the nutrition and several culinary properties of real eggs, making possible foods such as
Hollandaise sauce,
custard,
mayonnaise, and most baked goods with these substitutes.
Nutritional value
Chicken eggs are the most commonly eaten eggs. They supply all
essential amino acids for humans (a source of '
complete protein'), and provide several vitamins and minerals, including
retinol (vitamin A),
riboflavin (vitamin B
2),
folic acid (vitamin B
9),
vitamin B6,
vitamin B12,
choline,
iron,
calcium,
phosphorus and
potassium. Although not as abundant as red meats, eggs are a source of
CoQ10 depending on how they are prepared.
All of the egg's vitamins A,
D, and
E
are in the egg yolk. The egg is one of the few foods to naturally
contain vitamin D. 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 one study indicates the human body may 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, slightly less than half of the protein, and most of the other nutrients. It also contains all of the
choline,
and one yolk contains approximately half of the recommended daily
intake. Choline is an important nutrient for development of the brain,
and is said to be important for pregnant and nursing women to ensure
healthy fetal
brain development.
The diet of the laying hens can greatly affect the nutritional
quality of the eggs. For instance, chicken eggs that are especially high
in
omega 3 fatty acids are produced by feeding laying hens a diet containing
polyunsaturated fats and
kelp meal.
Pasture-raised free-range hens
which forage largely for their own food also tend to produce eggs with
higher nutritional quality in having less cholesterol and fats while
being several times higher in vitamins and omega 3 fatty acids than
standard factory eggs.
Focusing on the protein and crude fat content, a 2010 USDA study
determined there were no significant differences of these two
macronutrients in consumer chicken eggs.
Cooked eggs are easier to digest, as well as having a lower risk of
salmonellosis.
Health studies
Cholesterol and fat
More than half the calories found in eggs come from the fat in the
yolk; a large (50 gram) chicken egg contains approximately 5 grams of
fat. People on a low-cholesterol diet may need to reduce egg
consumption; however, only 27% of the fat in egg is
saturated fat (
palmitic,
stearic and
myristic acids). The
egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little, if any, fat.
There is debate over whether egg yolk presents a health risk. Some research suggests dietary
cholesterol increases the ratio of total to
HDL cholesterol and, therefore, adversely affects the body's cholesterol profile;
whereas other studies show that moderate consumption of eggs, up to one a day, does not appear to increase
heart disease risk in healthy individuals.
Harold McGee
argues that the cholesterol in the yolk is not what causes a problem,
because fat (in particular, saturated) is much more likely to raise
cholesterol levels than the actual consumption of cholesterol. In a randomized trial, Sacks et al.
found that adding one egg per day to the usual diet of 17
lactovegetarians whose habitual cholesterol intake was very low
(97 mg/day) significantly increased LDL cholesterol level by 12%.
Type 2 diabetes
Studies have shown conflicting results about a possible connection between egg consumption and
type two diabetes. A 1999
prospective study of over 117,000 people by the
Harvard School of Public Health concluded, in part, that "The apparent increased risk of
CHD associated with higher egg consumption among diabetic participants warrants further research."
A 2008 study by the Physicians' Health Study I (1982–2007) and the
Women's Health Study (1992–2007) determined the “data suggest that high
levels of egg consumption (daily) are associated with an increased risk
of type 2 diabetes.”
However, a study published in 2010 found no link between egg consumption and type 2 diabetes.
Cardiovascular risk
Eggs are one of the largest sources of
phosphatidylcholine (
lecithin) in the human diet.
A study published in the scientific journal
Nature showed that dietary phosphatidylcholine is digested by bacteria in the gut and eventually converted into the compound
TMAO, a compound linked with increased heart disease.
The 1999
Harvard School of Public Health
study of 37,851 men and 80,082 women concluded that its "findings
suggest that consumption of up to 1 egg per day is unlikely to have
substantial overall impact on the risk of
CHD or stroke among healthy men and women."
In a study of 4,000 people published in the
New England Journal of Medicine,
scientists found that eating eggs lead to significantly increased
levels of TMAO in the blood of study participants and that this in turn
led to significantly higher risk of heart attack and stroke after three
years of follow-up.
A 2007 study of nearly 10,000 adults demonstrated no correlation between moderate (six per week) egg consumption and
cardiovascular disease or
strokes, except in the subpopulation of
diabetic patients who presented an increased risk of
coronary heart disease.
One potential alternative explanation for the null finding is that
background dietary cholesterol may be so high in the usual Western diet
that adding somewhat more has little further effect on blood
cholesterol. Other research supports the idea that a high egg intake
increases cardiovascular risk in diabetic patients.
A 2009 prospective cohort study of over 21,000 individuals suggests
that "egg consumption up to 6/week has no major effect on the risk of
CVD
and mortality and that consumption of 7+/week is associated with a
modest increased risk of total mortality" in males, whereas among males
with diabetes, "any egg consumption is associated with an increased risk
of all-cause mortality and there was suggestive evidence for an
increased risk of
MI and
stroke".
A meta-analysis published in the British Medical Journal in 2013 found
no association between egg consumption and heart disease or stroke.
Contamination
Egg cleaning on a farm in Norway
A health issue associated with eggs is contamination by
pathogenic bacteria, such as
Salmonella enteritidis. Contamination of eggs exiting a female bird via the
cloaca may also occur with other members of the
Salmonella genus, so care must be taken to prevent the egg shell from becoming contaminated with
fecal
matter. In commercial practice in the US, eggs are quickly washed with a
sanitizing solution within minutes of being laid. The risk of infection
from raw or undercooked eggs is dependent in part upon the sanitary
conditions under which the hens are kept.
Health experts advise people to refrigerate washed eggs, use them
within two weeks, cook them thoroughly, and never consume raw eggs.
As with
meat, containers and surfaces that have been used to process raw eggs should not come in contact with ready-to-eat food.
A study by the U.S. Department of Agriculture in 2002 (Risk Analysis
April 2002 22(2):203-18) suggests the problem is not as prevalent as
once thought. It showed that of the 69 billion eggs produced annually,
only 2.3 million are contaminated with
Salmonella—equivalent to just one in every 30,000 eggs—thus showing
Salmonella infection is quite rarely induced by eggs. However, this has not been the case in other countries, where
Salmonella enteritidis and
Salmonella typhimurium infections due to egg consumptions are major concerns.
Egg shells act as
hermetic seals
that 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. In the
UK, the
British Egg Industry Council award the lions stamp to eggs that, among other things, come from hens that have been vaccinated against
Salmonella.
Food allergy
Main article:
Egg allergy
One of the most common
food allergies in infants is eggs.
Infants usually have the opportunity to grow out of this allergy during childhood, if exposure is minimized.
Allergic reactions against egg white are more common than reactions against egg yolks.
In addition to true allergic reactions, some people experience a
food intolerance to egg whites.
Food labeling practices in most developed countries now include eggs,
egg products and the processing of foods on equipment that also process
foods containing eggs in a special allergen alert section of the
ingredients on the labels.
Farming issues
Eggs for sale at a grocery store
Most commercially farmed chicken eggs intended for human consumption are unfertilized, since the laying hens are kept without
roosters. Fertile eggs can be eaten, with little nutritional difference to the unfertilized. Fertile eggs will not contain a developed
embryo,
as refrigeration temperatures inhibit cellular growth for an extended
time. Sometimes an embryo is allowed to develop but eaten before
hatching as with
balut.
Grading by quality and size
The US Department of Agriculture grades eggs by the interior quality of the egg (see
Haugh unit) and the appearance and condition of the egg shell. Eggs of any quality grade may differ in weight (size).
- U.S. Grade AA
- Eggs have whites that are thick and firm; yolks that are high,
round, and practically free from defects; and clean, unbroken shells.
- Grade AA and Grade A eggs are best for frying and poaching, where appearance is important.
- U.S. Grade A
- Eggs have characteristics of Grade AA eggs except the whites are "reasonably" firm.
- This is the quality most often sold in stores.
- U.S. Grade B
- Eggs have whites that may be thinner and yolks that may be wider and
flatter than eggs of higher grades. The shells must be unbroken, but
may show slight stains.
- This quality is seldom found in retail stores because they are
usually used to make liquid, frozen, and dried egg products, as well as
other egg-containing products.
In
Australia and the
European Union, eggs are graded by the hen farming method,
free range,
battery caged, etc.
Chicken eggs are also graded by
size for the purpose of sales.
Washing and refrigeration
In North America, legislation requires eggs to be washed and
refrigerated before being sold to cusumers. This is to remove natural
farm contaminants present in the cleanest farms and to prevent the
growth of bacteria. In Europe legislation requires the opposite. Washing
removes the natural protective cuticle on the egg and refrigeration
causes condensation which may promote bacteria growth.
Color of eggshell
White, speckled (red), and brown chicken eggs
Although egg color is a largely cosmetic issue, with no effect on egg
quality or taste, it is a major issue in production due to regional and
national preferences for specific colors, and the results of such
preferences on demand. For example, in most regions of the
United States, chicken eggs are generally white. In some parts of the
northeast of that country, particularly
New England,
where a television jingle for years proclaimed "brown eggs are local
eggs, and local eggs are fresh!", brown eggs are more common. Local
chicken breeds, including the
Rhode Island Red, lay brown eggs. Brown eggs are also preferred in
Costa Rica,
Ireland,
France, and the
United Kingdom. In
Brazil and
Poland, white chicken eggs are generally regarded as industrial, and brown or reddish ones are preferred. Small farms and
smallholdings,
particularly in economically advanced nations, may sell eggs of widely
varying colors and sizes, with combinations of white, brown, speckled
(red), green, and blue eggs in the same box or carton, while the
supermarkets at the same time sell mostly eggs from the larger
producers, of the color preferred in that nation or region.
These cultural trends have been observed for many years.
The New York Times reported during the Second World War that housewives in Boston preferred brown eggs and those in New York preferred white eggs. In February 1976, the British
New Scientist
magazine, in discussing issues of chicken egg color, stated "Housewives
are particularly fussy about the colour of their eggs, preferring even
to pay more for brown eggs although white eggs are just as good".
As a result of these trends, brown eggs are usually more expensive to
purchase in regions where white eggs are considered 'normal', due to
lower production.
In France and the United Kingdom it is very difficult to buy white
eggs, with most supermarkets supplying only the more popular brown eggs.
By direct contrast, in
Egypt
it is very hard to source brown eggs, as demand is almost entirely for
white ones, with the country's largest supplier describing white eggs as
"table eggs" and packaging brown eggs for export.
Research conducted in France in the 1970s demonstrated blue chicken eggs (as laid by certain breeds, including araucanas,
heritage skyline, and cream legbar) can be stronger and more resilient
to breakage, yet an article in New Scientist magazine (contemporary with
that research) stated there was little to no demand for blue-colored
eggs from housewives, despite the clear advantages.
Research at
Nihon University,
Japan
in 1990 revealed a number of different issues were important to
Japanese housewives when deciding which eggs to buy; however, color was a
distinct factor, with most Japanese housewives preferring the white
color.
Egg producers carefully consider cultural issues, as well as
commercial ones, when selecting the breed or breeds of chicken used for
production, as egg color varies between breeds.
Among producers and breeders, brown eggs are often referred to as
"tinted", while the speckled eggs preferred by some consumers are often
referred to as being "red" in color.
Living conditions of birds
Laying hens in battery cages
Commercial
factory farming
operations often involve raising the hens in small, crowded cages,
preventing the chickens from engaging in natural behaviors, such as
wing-flapping, dust-bathing, scratching, pecking, perching and
nest-building. Such restrictions can lead to pacing and
escape behavior.
Many hens confined to battery cages, and some raised in cage-free conditions, are
debeaked to prevent harming each other and
cannibalism.
According to critics of the practice, this can cause hens severe pain
to the point where some may refuse to eat and starve to death. Some hens
may be
force molted to increase egg quality and production level after the molting. Molting can be induced by extended feed withdrawal, water withdrawal or controlled lighting programs.
Laying hens are often slaughtered between 100 and 130 weeks of age, when their egg productivity starts to decline. 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 soon after they hatch.
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 in the United States of America, as there is no
legal definition or regulations for eggs labeled as free-range in that
country.
In the United States, increased public concern for
animal welfare
has pushed various egg producers to promote eggs under a variety of
standards. The most widespread standard in use is determined by
United Egg Producers through their voluntary program of certification.
The United Egg Producers program includes guidelines regarding housing,
food, water, air, living space, beak trimming, molting, handling, and
transportation, however, opponents such as
The Humane Society have alleged UEP Certification is misleading and allows a significant amount of unchecked animal cruelty.
Other standards include "Cage Free", "Natural", "Certified Humane", and "
Certified Organic".
Of these standards, "Certified Humane", which carries requirements for
stocking density and cage-free keeping and so on, and "Certified
Organic", which requires hens to have outdoor access and be fed only
organic vegetarian feed and so on, are the most stringent.
Effective 1 January 2012, the
European Union banned conventional battery cages for egg-laying hens, as outlined in EU Directive 1999/74/EC. The EU permits the use of "enriched"
furnished cages
that must meet certain space and amenity requirements. Egg producers in
many member states have objected to the new quality standards while in
some countries even furnished cages and family cages are subject to be
banned as well. The production standard of the eggs is visible on the
mandatory
egg marking where the EU egg code begins with 3 for caged chicken to 1 for free-range eggs and 0 for organic egg production.
Killing of male chicks
Main article:
Chick culling
In battery cage and free-range egg production, unwanted male chicks
are killed at birth during the process of securing a further generation
of egg-laying hens.
Cultural significance
A popular
Easter
tradition in some parts of the world is the decoration of hard-boiled
eggs (usually by dyeing, but often by spray-painting). Adults often hide
the eggs for children to find, an activity known as an Easter egg hunt.
A similar tradition of
egg painting exists in areas of the world influenced by the culture of
Persia. Before the spring
equinox in the Persian New Year tradition (called
Norouz), each family member decorates a hard-boiled egg and sets them together in a bowl.
The tradition of a
dancing egg is held during the feast of
Corpus Christi in Barcelona and other
Catalan
cities since the 16th century. It consists of an emptied egg,
positioned over the water jet from a fountain, which starts turning
without falling.
Although a food item, eggs are sometimes thrown at houses, cars, or people. This act, known commonly as "
egging" in the various
English-speaking countries, is a minor form of
vandalism and, therefore, usually a
criminal
offense and is capable of damaging property (egg whites can degrade
certain types of vehicle paint) as well as causing serious eye injury.
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 inexpensive and nonlethal, yet very messy when
broken.
