Eggs, Basic Facts & Nutrient Content

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Eggs, Basic Facts & Nutrient Content

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Air Cell

The empty space between the white and shell at the large end of the egg.

When an egg is first laid, it is warm. As it cools, the contents contract

and the inner shell membrane separates from the outer shell membrane to form

the air cell.

The candler uses the size of the air cell as one basis for determining

grade. In Grade AA eggs, the air cell may not exceed 1/8-inch in depth and is

about the size of a dime. The air cell of Grade A eggs may exceed 3/16-inch in

depth. For Grade B eggs, there is no limit on air cell size.

As the egg ages, moisture and carbon dioxide leave through the pores of the

shell, air enters to replace them and the air cell becomes larger.

Although the air cell usually forms in the large end of the egg, it

occasionally moves freely toward the uppermost point of the egg as the egg is

rotated. It is then called a free or floating air cell. If the main air cell

ruptures, resulting in one or more small separate air bubbles floating beneath

the

main air cell, it is known as a bubbly air cell.

You can see the air cell in the flattened end of a peeled, hard-cooked egg.

Albumen

Also known as egg white. Albumen accounts for most of an egg's liquid

weight, about 67%. It contains more than half the egg's total protein, niacin,

riboflavin, chlorine, magnesium, potassium, sodium and sulfur. The albumen

consists of 4 alternating layers of thick and thin consistencies.

From the yolk outward, they are designated as the inner thick or

chalaziferous white, the inner thin white, the outer thick white and the outer

thin

white. Egg white tends to thin out as an egg ages because its protein changes

in

character. That's why fresh eggs sit up tall and firm in the pan while older

ones tend to spread out.

Albumen is more opalescent than truly white. The cloudy appearance comes

from carbon dioxide. As the egg ages, carbon dioxide escapes, so the albumen of

older eggs is more transparent than that of fresher eggs.

When egg albumen is beaten vigorously, it foams and increases in volume 6 to

8 times. Egg foams are essential for making souffles, meringues, puffy

omelets, and angel food and sponge cakes.

Blood Spots

Also called meat spots. Occasionally found on an egg yolk. Contrary to

popular opinion, these tiny spots do not indicate a fertilized egg. Rather,

they

are caused by the rupture of a blood vessel on the yolk surface during

formation of the egg or by a similar accident in the wall of the oviduct. Less

than

1% of all eggs produced have blood spots.

Mass candling methods reveal most eggs with blood spots and those eggs are

removed but, even with electronic spotters, it is impossible to catch all of

them. As an egg ages, the yolk takes up water from the albumen to dilute the

blood spot so, in actuality, a blood spot indicates that the egg is fresh.

Both chemically and nutritionally, these eggs are fit to eat. The spot can be

removed with the tip of a knife, if you wish.

Carton Dates

Egg cartons from USDA-inspected plants must display a Julian date--the date

the eggs were packed. Although not required, they may also carry an

expiration date beyond which the eggs should not be sold. In USDA-inspected

plants,

this date cannot exceed 30 days after the pack date. It may be less through

choice of the packer or quantity purchaser such as your local supermarket

chain.

Plants not under USDA inspection are governed by laws of their states.

Chalaza

Ropey strands of egg white which anchor the yolk in place in the center of

the thick white. They are neither imperfections nor beginning embryos.

The more prominent the chalazae, the fresher the egg. Chalazae do not

interfere with the cooking or beating of the white and need not be removed,

although some cooks like to strain them from stirred custard.

Color

Egg shell and yolk color may vary, but color has nothing to do with egg

quality, flavor, nutritive value, cooking characteristics or shell thickness.

* Shell: The color comes from pigments in the outer layer of the shell and

may range in various breeds from white to deep brown. The breed of hen

determines the color of the shell. Breeds with white feathers and ear lobes lay

white eggs; breeds with red feathers and ear lobes lay brown eggs. White eggs

are

most in demand among American buyers. In some parts of the country, however,

particularly in New England, brown shells are preferred. The Rhode Island

Red, New Hampshire and Plymouth Rock are breeds that lay brown eggs. Since

brown-egg layers are slightly larger birds and require more food, brown eggs

are

usually more expensive than white.

* White: Egg albumen in raw eggs is opalescent and does not appear white

until it is beaten or cooked. A yellow or greenish cast in raw white may

indicate the presence of riboflavin. Cloudiness of the raw white is due to the

presence of carbon dioxide which has not had time to escape through the shell

and

thus indicates a very fresh egg.

On very rare occasions, a hard-cooked egg white may darken to a caramel

shade due to a high amount of iron in the cooking water or to a

carbonylamine-type reaction. Using fresh eggs and cooling them quickly after

cooking helps to

prevent this darkening.

* Yolk: color depends on the diet of the hen. If she gets plenty of

yellow-orange plant pigments known as xanthophylls, they will be deposited in

the

yolk. Hens fed mashes containing yellow corn and alfalfa meal lay eggs with

medium yellow yolks, while those eating wheat or barley yield lighter-colored

yolks. A colorless diet, such as white cornmeal produces almost colorless yolks.

Natural yellow-orange substances such as marigold petals may be added to

light-colored feeds to enhance yolk color. Artificial color additives are not

permitted. Gold or lemon-colored yolks are preferred by most buyers in this

country. Yolk pigments are relatively stable and are not lost or changed in

cooking.

Sometimes there is a greenish ring around hard-cooked egg yolks. It is the

result of sulfur and iron compounds in the egg reacting at the surface of the

yolk. It may occur when eggs are overcooked or when there is a high amount of

iron in the cooking water. Although the color may be a bit unappealing, the

eggs are still wholesome and nutritious and their flavor is unaffected. Gre

enish yolks can best be avoided by using the proper cooking time and

temperature and by rapidly cooling the cooked eggs.

Occasionally several concentric green rings may be seen in hard-cooked egg

yolks. A yolk develops within the hen in rings. Iron in the hen's feed or

water as the rings are formed may cause this coloring. Sometimes a large batch

of

scrambled eggs may turn green. Although not pretty, the color change is

harmless.

It is due to a chemical change brought on by heat and occurs when eggs are

cooked at too high a temperature, held for too long or both. Using stainless

steel equipment and low cooking temperature, cooking in small batches and

serving as soon as possible after cooking will help to prevent this. If it is

necessary to hold scrambled eggs for a short time before serving, it helps to

avoid direct heat. Place a pan of hot water between the pan of eggs and the heat

source.

Egg Quality

 

Grade AA Grade A Grade B Break Out Appearance Covers a small area.

Covers a moderate area. Covers a wide area. Albumen Appearance White is

thick

and stands high; chalaza prominent. White is reasonably thick, stands fairly

high; chalaza prominent. Small amount of thick white; chalaza small or

absent. Appears weak and watery. Yolk Appearance Yolk is firm, round and

high.

Yolk is firm and stands fairly high. Yolk is somewhat flattened and enlarged.

Shell Appearance Approximates usual shape; generally clean,* unbroken;

ridges/rough spots that do not affect the shell strength are permitted.

Abnormal shape; some slight stained areas permitted; unbroken; pronounced

ridges/thin spots permitted. Usage Ideal for any use, but are especially

desirable

for poaching, frying and cooking in shell. Ideal for any use, but are

especially desirable for poaching, frying and cooking in shell. Good for

scrambling,

baking, and as an ingredient in other foods.

*An egg may be considered clean if it has only very small specks, stains or

cage marks. Source: USDA

Grade AA: A 'Grade AA' egg will stand up tall. The yolk is firm and the area

covered by the white is small. There is a large proportion of thick white to

thin white.

Grade A: A 'Grade A' egg covers a relatively small area. The yolk is round

and upstanding. The thick white is large in proportion to the thin white and

stands fairly well around the yolk.

Grade B: A 'Grade B' egg spreads out more. The yolk is flattened and there

is about as much (or more) thin white as thick white.

Fertile Eggs

Eggs which can be incubated and developed into chicks. Fertile eggs are not

more nutritious than nonfertile eggs, do not keep as well as nonfertile eggs

and are more expensive to produce. Fertile eggs may contain a small amount of

male hormone, but there are no known advantages.

Free-Range Eggs

True free-range eggs are those produced by hens raised outdoors or that have

daily access to the outdoors. Due to seasonal conditions, however, few hens

are actually raised outdoors. Some egg farms are indoor floor operations and

these are sometimes erroneously referred to as free-range operations. Due to

higher production costs and lower volume per farm, free-range eggs are

generally more expensive.

The nutrient content of eggs is not affected by whether hens are raised

free-range or in floor or cage operations. [bee's note: this is not true. A

chicken's natural diet includes worms, insects, bugs, beetles, etc., like any

other bird, which are a very important source of oil soluble vitamins and fat.

This definitely influences the nutrients contained in their eggs.]

Freshness

How recently an egg was laid has a bearing on its freshness but is only one

of many factors. The temperature at which it is held, the humidity and the

handling all play their part. These variables are so important that an egg one

week old, held under ideal conditions, can be fresher than an egg left at

room temperature for one day. The ideal conditions are temperatures that don't

go above 40°F. (4°C.) and a relative humidity of 70 to 80%.

Proper handling means prompt gathering, washing and oiling of the eggs

within a few hours after laying. Most commercially produced eggs reach

supermarkets within a few days of leaving the laying house. If the market and

the buyer

handle them properly, they will still be fresh when they reach the table.

It is not true that freshness can be judged by placing an egg in salt water.

A carefully controlled brine test is sometimes used to judge shell thickness

of eggs for hatching purposes but has no application to freshness of table

eggs.

How important is " freshness " ? As an egg ages, the white becomes thinner and

the yolk becomes flatter. These changes do not have any great effect on the

nutritional quality of the egg or its functional cooking properties in

recipes. Appearance may be affected, though. When poached or fried, the fresher

the

egg, the more it will hold its shape rather than spread out in the pan. On

the other hand, if you hard cook eggs that are at least a week old, you'll find

them easier to peel after cooking and cooling than fresher eggs.

Germinal Disc

The entrance of the latebra, the channel leading to the center of the yolk.

The germinal disc is barely noticeable as a slight depression on the surface

of the yolk. When the egg is fertilized, sperm enter by way of the germinal

disc, travel to the center and a chick embryo starts to form.

Membranes:

* Shell Membranes: Just inside the shell are two shell membranes,

inner and outer. After the egg is laid and it begins to cool, an air cell forms

between these two layers at the large end of the egg.

* Vitelline Membrane: This is the covering of the yolk. Its strength

protects the yolk from breaking. The vitelline membrane is weakest at the

germinal disc and tends to become more fragile as the egg ages.

Grading

Classification determined by interior and exterior quality and designated by

letters — AA, A and B. In many egg packing plants, the USDA provides a

grading service for shell eggs. Its official grade shield certifies that the

eggs

have been graded under federal supervision according to USDA standards and

regulations. The grading service is not mandatory. Other eggs are packed under

state regulations which must meet or exceed federal standards.

In the grading process, eggs are examined for both interior and exterior

quality and are sorted according to weight (size). Grade quality and size are

not related to one another. In descending order of quality, grades are AA, A

and B.

There is no difference in nutritive value between the different grades.

Because production and marketing methods have become very efficient, eggs

move so rapidly from laying house to market that you will find very little

difference in quality between Grades AA and A.

Although grade B eggs are just as wholesome to eat, they rate lower in

appearance when broken out. Almost no Grade B's find their way to the retail

supermarket. Some go to institutional egg users such as bakeries or foodservice

operations, but most go to egg breakers for use in egg products.

Julian Dates

Starting with January 1 as number 1 and ending with December 31 as 365,

these numbers represent the consecutive days of the year. This numbering system

is sometimes used on egg cartons to denote the day the eggs are packed. Fresh

shell eggs can be stored in their cartons in the refrigerator for 4 to 5

weeks beyond this date with insignificant quality loss.

Organic Eggs

These are eggs from hens fed rations having ingredients that were grown

without pesticides, fungicides, herbicides or commercial fertilizers. No

commercial laying hen's rations ever contain hormones.

Due to higher production costs and lower volume per farm, organic eggs are

more expensive than eggs from hens fed conventional feed. The nutrient content

of eggs is not affected by whether or not the ration is organic [bee's note:

However the nutrient content of eggs is affected by the foods eaten.

Certified organic free-range eggs from chickens eating their natural diet,

which

includes insects, bugs, worms, beetles and other meats, provides the most

nutritious eggs.]

Shell

The egg's outer covering, accounting for about 9 to l2% of its total weight

depending on egg size. The shell is the egg's first line of defense against

bacterial contamination.

The shell is largely composed of calcium carbonate (about 94%) with small

amounts of magnesium carbonate, calcium phosphate and other organic matter

including protein.

Shell strength is greatly influenced by the minerals and vitamins in the

hen's diet, particularly calcium, phosphorus, manganese and Vitamin D. If the

diet is deficient in calcium, for instance, the hen will produce a thin or

soft-shelled egg or possibly an egg with no shell at all.

Occasionally an egg may be prematurely expelled from the uterus due to

injury or excitement. In this case, the shell has not had time to be completely

formed. Shell thickness is also related to egg size which, in turn, is related

to the hen's age. As the hen ages, egg size increases. The same amount of

shell material which covers a smaller egg must be " stretched " to cover a larger

one, hence the shell is thinner.

Seven to 17 thousand tiny pores are distributed over the shell surface, a

greater number at the large end. As the egg ages, these tiny holes permit

moisture and carbon dioxide to move out and air to move in to form the air

cell.

The shell is covered with a protective coating called the cuticle or bloom. By

blocking the pores, the cuticle helps to preserve freshness and prevent

microbial contamination of the contents.

Uses for eggshells vary from the thrifty (compost) to the creative

(decorating). [bee's note: eggshells can also be ground up and consumed for

calcium

and other minerals.]

Size

Several factors influence the size of an egg. The major factor is the age of

the hen. As the hen ages, her eggs increase in size.

The breed of hen from which the egg comes is a second factor. Weight of the

bird is another. Pullets significantly underweight at sexual maturity will

produce small eggs.

Environmental factors that lower egg weights are heat, stress, overcrowding

and poor nutrition.

All of these variables are of great importance to the egg producer. Even a

slight shift in egg weight influences size classification and size is one of

the factors considered when eggs are priced. Careful flock management benefits

both the hens and the producer.

Egg sizes are Jumbo, Extra Large, Large, Medium, Small and Peewee. Medium,

Large and Extra Large are the sizes most commonly available.

Sizes are classified according to minimum net weight expressed in ounces per

dozen.

Size Equivalents

Although any size egg may be used for frying, scrambling, cooking in the

shell or poaching, most recipes for baked dishes such as custards and cakes are

based on the use of Large eggs. To substitute another size, use the following

chart. Size Equivalents Large Jumbo X-Large Medium Small 1 1 1

1 1 2 2 2 2 3 3 2 3 3 4 4 3 4 5 5 5 4 4 6 7 6 5

5 7 8

 

To Make 1 Cup Egg Size Whole Whites Yolks Jumbo 4 5 11 X-Large 4

6 12 Large 5 7 14 Medium 5 8 16 Small 6 9 18

Yolk

The yolk or yellow portion makes up about 33% of the liquid weight of the

egg. It contains all of the fat in the egg and a little less than half of the

protein.

With the exception of riboflavin and niacin, the yolk contains a higher

proportion of the egg's vitamins than the white. All of the egg's vitamins A, D

and E are in the yolk. Egg yolks are one of the few foods naturally containing

vitamin D.

The yolk also contains more phosphorus, manganese, iron, iodine, copper, and

calcium than the white, and it contains all of the zinc. The yolk of a Large

egg contains about 59 calories.

Double-yolked eggs are often produced by young hens whose egg production

cycles are not yet completely synchronized. They're often produced, too, by

hens

who are old enough to produce Extra Large eggs. Genetics is a factor, also.

Occasionally a hen will produce double-yolked eggs throughout her egg-laying

career. It is rare, but not unusual, for a young hen to produce an egg with

no yolk at all.

In fertilized eggs, the yolk is the site of embryo formation. It is the yolk

which is responsible for the egg's emulsifying properties.

Reference

_Basic Egg Facts_ (http://www.aeb.org/LearnMore/EggFacts.htm)