Egg

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Table of contents

1 Source 2 What is an egg? 3 Common egg questions 3.1 What causes blood spots? 3.2 Why do some hard-cooked eggs have a greenish ring around the yolk? 3.3 Is there a diffrence between white or brown shelled eggs? 3.4 How long will eggs keep? 3.5 What is the best way to store eggs? 3.6 Is it safe to eat raw eggs? 3.7 What are the stringy white pices in egg whites? 3.8 Are eggs an economical food? 3.9 Are fertile eggs more nutritious? 3.10 Why are some hard-cooked eggs difficult to peel? 3.11 Why is an egg white sometimes cloudy, or has a greenish or yellow cast to it? 4 Egg cooking terms 5 Egg composition 5.1 AIR CELL 5.2 ALBUMEN 5.3 CHALAZA 5.4 GERMINAL DISC 5.5 MEMBRANES 5.5.1 Vitelline Membrane 5.6 SHELL 5.7 Yolk

Source

The source of this page is http://www.aeb.org (http://www.aeb.org).

What is an egg?

An egg is the round or oval female reproductive body of various animals, including insects, reptiles, amphibians, fishes, and fowl (especially a hen) used as food, consisting usually of an embryo surrounded by nutrient material and a protective covering.

Common egg questions

What causes blood spots?

Small spots of blood (sometimes called "meat" spots) are occasionally found in an egg yolk. These do not indicate a fertile egg; they are caused by the rupture of a blood vessel on the yolk surface during formation of the egg. Most eggs with blood spots are removed during the grading process but a few may escape detection. As an egg ages, water moves from the albumen into the yolk, diluting the blood spot. Thus, a visible blood spot actually indicates a fresh egg. Such eggs are suitable for consumption. The spot can be removed with the tip of a knife, if you wish.

Why do some hard-cooked eggs have a greenish ring around the yolk?

The harmless greenish ring is due to an iron and sulfur compound which forms when eggs are overcooked or not cooled quickly.

Is there a diffrence between white or brown shelled eggs?

No. Shell color is determined by the breed of hen and is not related to quality, nutrients, flavor or cooking characteristics. Since brown egg layers are slightly larger birds and require more food, brown eggs are usually more expensive than white.

How long will eggs keep?

Fresh shell eggs can be kept refrigerated in their carton for at least 4 - 5 weeks beyond the pack date. Quality losses should be insignificant if the eggs are refrigerated as soon as possible after purchase from a refrigerated case.

Hard cooked eggs should be kept in the refrigerator for up to one week.

What is the best way to store eggs?

Store eggs in their carton because eggs can absorb refrigerator odors.

Is it safe to eat raw eggs?

The risk of food poisoning from eggs is highest with raw and lightly-cooked dishes. It's best not to serve raw or lightly-cooked dishes made with eggs.

What are the stringy white pices in egg whites?

These rope-like strands of egg white, called chalazae (ka-LAY-zee) are not imperfections or beginning embryos but a natural, edible part of the egg. They keep the yolk centered in the thick white.

Are eggs an economical food?

Eggs are one of today's best food buys. A dozen Large eggs weighs 1 ½ pounds so at 90¢ a dozen, eggs are only 60¢ per pound. Eggs supply high-quality protein and a variety of important vitamins and minerals at a very low price.

Are fertile eggs more nutritious?

Fertile eggs are not more nutritious than nonfertile eggs. They do not keep as well as nonfertile eggs and are more expensive to produce.

Why are some hard-cooked eggs difficult to peel?

Fresh eggs may be difficult to peel. Those which have been stored for a week to 10 days before cooking will usually peel more easily.

Why is an egg white sometimes cloudy, or has a greenish or yellow cast to it?

Cloudiness of raw white is due to the presence of carbon dioxide which has not had time to escape through the shell and is an indication of a very fresh egg. A slight yellow or greenish cast in raw white may indicate the presence of riboflavin.

Egg cooking terms

Slightly beaten

Well beaten

Thick and lemon-colored

Separated

Stiff, but not dry

Stiff, peaks form

Soft peaks or piles softly

Gently folded

Curdling

Egg composition

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.

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.

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

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.

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).

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.