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Eggs Facts
Everything you ever needed to know about eggs.
Keeping eggs fresh
Keep eggs in the fridge until you need them. The date stamp on your carton will tell you how long they will stay fresh for. Eggs lose their quality very quickly at room temperature, so refrigerate them immediately after purchase.
Look for shells that are clean and whole. Cracked eggs are always removed when cartons are being packed but if one cracks on the way to the store it’s safer to throw it away, or give it to your pet as a tasty treat!
Size
Have you ever found an egg in your carton which is smaller than the rest? Egg sizing is done by the egg’s weight, rather than its circumference. Many things contribute to the weight (or density) of an egg, for example the age of the hen (younger hens lay heavier, smaller eggs) and the amount of water in the egg (in summer hens drink more water which makes the eggs lighter).
Bloom
Egg shells are covered with a natural coating that seals its pores. This helps to prevent bacteria from getting inside the shell and reduces moisture loss. Wiping or washing eggs removes the protective coating and reduces the lifetime of the egg.
Candling
When eggs are being graded they roll over a bright light which makes the egg transparent so the grader can check the inside of the egg for quality. Long ago, candling was done by holding the egg up before a lit candle, which is how this part of the grading process got its name. Today eggs pass over high-intensity lights on rollers so all of the egg can be viewed.
Chalaza
The yolk is anchored to the white by tiny strands of egg white called chalaza. The more prominent the chalazae, the fresher the egg.
Colour
Egg shell and yolk colour will vary depending on the diet of the hen. Colour variations have no effect on the quality, flavour, or nutritional value of the egg. The breed of hen determines the colour of the shell. Hens with white feathers and ear lobes lay white eggs; hens with red feathers and ear lobes lay brown eggs. Egg white (albumen) is actually clear when raw and only becomes white in colour when beaten or cooked. Using fresh eggs and cooling them quickly after cooking helps prevent darkening of the egg white.
The 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. The yolk contains all this goodness because in fertilised eggs the yolk is the site of embryo formation.
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 sunshine vitamin). 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. It is the yolk which is responsible for the egg's emulsifying properties in cooking.
Yolk colour - raw
Yolk colour depends solely on the diet of the hen as artificial additives to enhance yolk colour are not permitted. If she gets plenty of yellow-orange plant pigments (xanthophylls), these will be deposited into the yolk. Hens fed mashes containing yellow corn lay eggs with medium yellow yolks. Those eating wheat or barley lay lighter-colour yolks. Golden yolks are preferred by most New Zealanders.
Yolk colour – cooked
A greenish ring around a hard-cooked egg yolk may be the result of sulphur and iron compounds in the egg reacting at the surface of the yolk, overcooking or a high proportion of iron in the cooking water. The eggs are still wholesome and nutritious, and their flavour is unaffected.
Greenish yolks can best be avoided by using the proper cooking time and temperature, and by rapidly cooling the cooked eggs in cold water.
Double-yolkers
Double-yolkers are created when a hen releases two yolks at the same time. This is quite common in young hens whose cycles may not be perfectly synchronised. Older hens will sometimes produce a double-yolker in an Extra Large egg. Occasionally a hen will produce double-yolker 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!
Egg anatomy
Freshness
The best before date on a carton of eggs tells you how long the eggs inside it stay ‘fresh’ if they are kept refrigerated after purchase. During this time (usually about 35 days) there is little change in the nutritional value of the egg, but the appearance and qualities of the egg may change as the egg ages. Poached or fried eggs hold their shape better the fresher the egg, but hard boiled eggs are much easier to peel if the eggs are at least one week old.
Temperature, humidity and handling all contribute to freshness. A one week old egg kept in ideal conditions can be fresher than an egg left at room temperature for one day.
Most commercially produced eggs reach supermarkets within a few days of being laid and in New Zealand it is also possible to purchase eggs which are guaranteed to be sold the same day they are laid.
Blood spots
Occasionally small blood spots may be found on an egg yolk. These are caused by the rupture of a blood vessel on the yolk surface during egg formation. Less than 1% of all eggs produced have blood spots as they are normally removed during the candling process. The egg can be eaten as normal or the spot can be removed with the tip of a knife. The tiny red spots do not indicate a fertilised egg.
Which came first, the chicken or the egg?
In the science of evolution, both chickens and eggs pre-date man so unfortunately there was no-one around to see, but according to the Bible, the chicken came first.
"And the evening and the morning were the fourth day. And God said, 'Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven'." Genesis 1:19-20. (Chickens are a type of fowl).
Farming and Production Methods
Cage Systems: Birds in cage systems are continuously housed in cages within a shed.
Barn Systems: Birds in barn systems are free to roam within a shed which may or may not have vertical levels. The floor may be based on litter or other material such as slats or wire mesh.
Free Range Systems: Birds in free-range systems range outdoors and have indoor shelter for night and inclement weather conditions.
How is an egg made?
Firstly the hen releases a yolk from her ovary. The infundibulum (also known as the funnel), holds the yolk for about 15 minutes (this is where fertilisation would take place if there was a rooster), before it passes to the magnum, where after three hours the white is formed. As the white (albumen) is deposited around the yolk it rotates, twisting the albuminous fibres to form the chalazae.
The next site of activity is the isthmus where the two shell membranes are formed in about 1¼ hours. The egg has now reached it full size and shape. It passes along to the uterus to acquire, after 19 hours, its shell, shell colour and bloom, or protective coating. After a few minutes' pause in the vagina, the uterus inverts the cloaca (the junction of the digestive, urinary and reproductive systems) and the vent and the egg is laid.
A hen requires between 24 and 26 hours to produce an egg.
Thirty minutes after laying an egg she starts all over again.
Most female animals have two functioning ovaries, but hens only use one, their left. The right ovary stays dormant.
A female hen is born with thousands of tiny ova which will one day become egg yolks.
A double-yolker egg is the result of two yolks being released at the same time.
During formation, the egg moves through the oviduct small end first.
Just before laying, it is rotated and laid large end first.
Laying an egg is known as oviposition.
The size of the eggs increase as a hen gets older.
What shape is an egg shape?
If you said an egg is an oval, you're right! The actual mathematical description is an oblate spheroid.
The word spheroid means that the egg is like a sphere, but isn't exactly a sphere. That's because an egg isn't perfectly round. The word oblate means that the poles of the egg are flattened or depressed.
So, an egg is a not-quite-round sphere with flattened sides. You could also say that it's an oval with one end larger than the other.
What is the best way to store raw eggs?
Keep eggs or egg products (mayonnaise etc) refrigerated at 4C or below when you're not cooking or eating them. These foods should not be left at room temperature for more than 2 hours, including the time you use to prepare and serve them.
Eggs are porous, which means smells and liquid can be absorbed by the tiny pores on the eggs shell. Storing eggs in their cartons in the fridge helps prevent this. Place egg cartons on a middle or lower shelf rather than in the door of the fridge so the temperature is more consistent.
How can I store leftover egg whites and yolks?
You can refrigerate raw whites for up to 4 days and unbroken raw yolks, covered with water, for up to 2 days in a tightly sealed container. If you can't use the yolks quickly enough, hard cook them just as you would cook whole eggs in the shell, drain them well and refrigerate them in a tightly sealed container for up to 4 or 5 days.
For longer storage, freeze raw whites, sugared or salted yolks and cooked yolks for up to 1 year.
To freeze egg whites, break and separate the eggs, one at a time, making sure that no yolk gets in the whites. Pour the whites into freezer containers, seal the containers tightly, label with the number of egg whites and the date and freeze. For faster thawing and easier measuring, first freeze each white in an ice cube tray and then transfer to a freezer bag or container. Substitute 2 tablespoons thawed egg white for 1 Large fresh white.
Raw egg yolks require special treatment because the yolk's gelation property causes it to thicken or gel when frozen making it almost impossible to use. Beat in either 1/8 teaspoon salt or 1 1/2 teaspoons sugar for each 1/4 cup egg yolks (4 Large yolks). Label the container with the number of yolks, the date and whether you've added salt (for main dishes) or sweetener (for baking or desserts) and freeze. Substitute 1 tablespoon thawed egg yolk for 1 Large fresh yolk.
How safe are eggs?
The risk of getting an illness from eggs is very low. However, the nutrients that make eggs a high-quality food for humans are also a good growth medium for bacteria. In addition to food, bacteria also need moisture, a favourable temperature and time in order to multiply and increase the risk of illness. In the rare event that an egg contains bacteria, you can reduce the risk by proper chilling and eliminate it by proper cooking. When you handle eggs with care, they pose no greater food-safety risk than any other perishable food.
What causes blood spots?
Small spots of blood 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. Such eggs are suitable for consumption and the spot can be easily removed with the tip of a knife.
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.
What is the difference between brown and white eggs?
Brown eggs come from brown feathered hens and white eggs from white feathered hens. Shell colour varies with the breed of hen and is not related to quality, nutrients, flavour or cooking characteristics.
Is it safe to eat raw eggs?
It's best not to serve raw or lightly cooked dishes made with eggs. The risk of food poisoning from eggs is highest with raw and lightly cooked dishes.
What are the stringy white pieces in egg whites?
These edible rope-like strands of egg white, called chalazae (ka-LAY-zee) keep the yolk centred in the thick white.
Are eggs an economical food?
Eggs are one of today's best food buys. Eggs supply high-quality protein and a variety of important vitamins and minerals at a very low price.
Why are some hard-cooked eggs difficult to peel?
Fresh eggs can be difficult to peel. The best eggs to use for peeling are more than a week old.
Why is an egg white sometimes cloudy or has a yellow of greenish colour 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.
Interesting Facts and Figures
A hen requires 24 to 26 hours to produce an egg.
Thirty minutes later, she starts all over again.
The eggshell may have as many as 17,000 tiny pores over its surface. Through them, the egg can absorb flavours and odours.
Eggs age more in one day at room temperature than in one week in the refrigerator.
Hens with white feathers and ear lobes produce white shelled eggs. Hens with red feathers and red ear lobes produce brown shelled eggs.
To tell if an egg is raw or hard-cooked, spin it! If the egg spins easily, it is hard-cooked but if it wobbles, it is raw.
If an egg is accidentally dropped on the floor, sprinkle it heavily with salt for easy clean up.
Egg yolks are one of the few foods that naturally contain Vitamin D.
Yolk colour depends on the diet of the hen. Natural yellow-orange substances such as marigold petals may be added to light-colored feeds to enhance colours. Artificial colour additives are not permitted.
Eggs are nutritious for many pets as well as humans and are often an important part of prepared pet food formulas.
A pullet is a ‘young’ hen (like a heifer is a ‘young’ cow)
The egg shell accounts for about 9 to l2% of its total weight.
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.
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.
Eggs can be an important source of complete protein for vegetarians. One egg = 1 ounce of lean meat, fish or poultry.
Egg Legends
Stories about eggs go back to the earliest memories of man.
In Sanskrit, the sacred language of the Hindus, it is written that a cosmic egg contained a spirit that would be born, die and be reborn.
The Egyptians believed that their god Ptah created the egg out of the sun and moon. Phoenicians thought that two halves of a very large egg split open producing heaven and earth.
Because of its connections with new life, the egg has been touted as both an aphrodisiac and fertility insurance. Central European peasants rubbed eggs on their ploughs hoping to improve the crops.
The French bride broke an egg on the doorstep before entering her new home to assure a large family.
