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Three eggs on a pink surface
Photo: Maria Ionov, Unsplash

Celebrate Easter with a little more knowledge about eggs


What came first, the chicken or the egg? We know that hens are needed in order for us to be able to eat eggs during Easter. But how does it work when the egg is formed and why is the shell perforated with thousands of holes? Kristina Snuttan Sundell, Professor of zoology, teaches us more about the centerpiece of the Easter table.

There are many different species of hens in the world, but they mostly originate from the red jungle hen, gallus gallus, found in Southeast Asia.

Kristina Snuttan Sundell
Kristina Snuttan Sundell, professor i zoologi
Photo: Johan Wingborg

"I've seen chickens like that in Nepal. The roosters are colorful and neat and look like a mixture of rooster and pheasant, the hens are grey-brown. They sneak around under the bushes and are not very easy to spot," says Kristina Snuttan Sundell.

Gallus gallus domesticus – Easter hero

According to Statistics Sweden, there are approximately nine million descendants of the indigenous hens in Southeast Asia in Sweden. The fact that there are so many domestic hens, or gallus gallus domesticus as they are called in Latin, should make anybody who celebrate Easter and who likes eggs, very happy. During Easter week, Swedes' egg consumption increases by double compared to the other 51 weeks of the year, and according to the industry body Svenska ägg, as many as six million eggs are being consumed per hour on Easter Eve. 

Creation of the egg

Chickens begin laying eggs when they are five or six months old. Eggs from young hens often have harder shells and are smaller than eggs from older hens. This is because the hen incorporates about the same amount of calcium in the shell no matter how large the egg is, which makes a smaller egg with less surface area thicker and harder.

"It is more frequent to find two egg yolks in eggs from the younger hens. It takes a while for the egg-laying process to be synchronized and therefore the hen can release two egg yolks from the ovary at the same time”.

Once released, the yolk wanders down the oviduct and where first the egg white is formed and envelops the yolk. Finally, the shell is formed on the egg.

"It happens in the egg gland and is the most demanding step. It takes 20-21 hours for the shell to be formed, making it impossible for the hen to lay more than one egg per day”.

Perforated shells 

Perhaps an unknown fact for many is that the eggshell has many thousands of small holes in it. 

"There are pores so that the chicken inside a fertilized egg can "breathe", that is, get oxygen for all processes in the body as it develops and grows”.

These pores can also help us humans if we want to find out if the egg in our refrigerator at home is fresh or not.  Air is constantly leaking through the pores of the eggshell. The air accumulates at the blunt end of the egg, where the shell membranes divide so that an air bladder can form. The older the egg, the more air in the bladder. 

So if you put an egg in a bowl of water and it sinks, then it is a really fresh egg with only a small air bladder. Old eggs, on the other hand, have a large air bladder, which makes it float in the water. This may be a sign that this particular egg should not be allowed on the Easter table, along with the other eggs.

"But the best thing is to trust your nose, so crack the egg and smell it, if it smells good, it's good to use in the omelet," Kristina Snuttan Sundell.

By: Ulrika Lundin, phone: +46 70 775 8851