It is a rare occurrence. When two chicks hatch from the same egg, the egg usually has two yolks. Usually, one embryo out competes the other and only one chick survives to hatch. Many time both embryos die before hatch.
They're most common when chickens start laying, before their system settles into a steady groove, but as the double yolk chicken breed shows, can be bred for. If both the ovum in the yolk are fertilised, they can both become viable (if a bit squashy) chicks.
Double-yolk eggs are a byproduct of rapid ovulation. That means two yolks are released in quick succession into a hen's oviduct (aka fallopian tube) and end up in the same shell. Typically, yolks are released about an hour apart, but hormonal changes or a hyperactive ovary will cause double releases.
By themselves, double yolks are fairly rare – you might find them in 1 of every 1,000 eggs. These eggs typically come from our younger hens who are still learning how to lay eggs. As you might expect, double yolked egg shells tend to be pretty big. In fact, they are usually graded 'Super Jumbo.
Finding a double yolk in an egg means someone in the immediate family is pregnant. If she already knows she is pregnant, it means she will have twins. Chances of finding a double-yolked egg are about one in 1,000.
The British Egg Information Service estimates a double yolk to happen once in every 1,000 eggs, and a triple yolk to happen once in every in 25 million eggs.
A one-in-25-million chance
"I managed to find some data from the British Egg Information Service suggesting a double-yolk egg is about one in 1,000 and a triple-yolk egg is about one in 25 million," she said.
Odds of quadruple-yolk egg are one in 11 billion
But what she had actually just cracked open was a quadruple-yolk egg. According to the British Egg Information Service, the odds of discovering a quadruple-yolker are one in 11 billion, according to a press release from Dakota Layers.
Even more rare is an egg with more than 2 yolks. Triple yolkers occur from time to time, and in fact, it's possible to get more yolks in an egg.
The odds of finding one of the these scarce eggs is said to be 1,000 to one, so theoretically the odds on finding ten in a row is 1,000,000,000,000,000,000,000,000,000,000 - or a quintillion - to one.
In many cultures and religions, a double yolk is a good thing; luck is on the way. Old folklore tells us someone close to you might be having twins or a new beginning is on the horizon. Or you just cracked into the about one-in-1,000 egg that has a double yolk.
So, ignoring all other factors, the chances of getting four double-yolk eggs in a row from a single carton should be (1/1,000) x (1/1,000) x (1/1,000) x (1/1,000), or one in every trillion.
Double yolked eggs can in most cases be used on a one-for-one basis for regular eggs in baking. You will find that the cakes will be richer as the yolks contain more fats but, as in using duck eggs for baking, this would be considered a positive by most people.
"They grade for size of the egg and for shell strength," Smith says. "They want uniformity." And, by definition, a double-yolker is not uniform. As a result, these jumbos — whether they foretell good luck or a scrambled future of misfortune — nowadays rarely make it to the grocery store.
Double yolk eggs typically come from younger pullets (hens) as they begin to lay. Breeds most likely to give you a double yolker include Leghorns and Rhode Island Reds.
Any breed can lay a double yolked egg, but it may be more common from breeds that are good layers, like Rhode Island Reds, Sussex, and Leghorns. Double yolkers are a favorite for over easy eggs!
According to Mashable, getting 12 double-yolk eggs in a row is super unlikely. The odds of getting just one double-yolked egg is one in 1,000, six in a row is one in a quintillion.
Among purebred brown egg layers, some of the largest eggs are produced by Jersey Giants and New Hampshires, both of which can be expected to lay large to extra-large eggs. Other layers of large brown eggs include the Delaware, Plymouth Rock, Rhode Island Red, Rhode Island White, and Sussex.
Though the egg-inside-of-an-egg phenomenon is rare, it does happen. It's due to a counter-peristalsis contraction, which happens when an egg is pushed back up into the chicken's reproductive system and becomes embedded in another newly forming egg.
A century egg tastes rich, complex, and pungent, like ripe blue cheese with a very faint hint of ammonia. (A spoiled century egg has a strong ammonia scent.)
Yolkless eggs are actually common enough that chicken keepers have a number of names for them—fairy egg, witch egg, rooster egg, oops eggs, dwarf egg, wind egg, and, most commonly, fart egg.
A genetically engineered hen is able to produce "golden eggs" containing a very particular protein (interferon beta) that may help treat diseases as diverse as cancer, hepatitis, and multiple sclerosis (MS).
A double yolk occurs when a chicken releases two yolks into the same shell and are usually produced by young chickens whose reproductive systems have not fully matured. Double yolks can also come from older chickens nearing the end of their egg producing period. Eggs with double yolks are perfectly safe to eat.
And, according to the Guinness World Records, the world's largest chicken egg, which was nine inches in diameter and had five yolks. Guinness World Records aside, the greatest number of yolks found in a single chicken egg is said to be nine. Yep, nine yolks in one egg.
Coming across a white yolk is perfectly natural, albeit, a little rare in the United States.