Why do some eggs float in water?

Eggs are a great way to start the day - or finish it. Fried, poached, boiled or scrambled, they are a great food to have on any occasion, breakfast, lunch or dinner. Eggs are full of protein, great for building muscle and people who do a lot of exercise.

Eggs usually have a reasonably long shelf life when kept in a cold place like a refrigerator - often up to four weeks or more.

But have you ever placed an egg in a glass of water? There are two different reactions that an egg can have to being placed in a tall glass of water.

Some eggs will sink in water. Other eggs will float in water. So of course the important question is... Why do some eggs float in water?

Rotten eggs will float in water.
Rotten eggs will float in water.

So what does it mean when an Egg floats?

Rotten eggs will float in water.

Fresh and edible eggs will sink all the way to the bottom of the glass.

There are varying degrees between the two. If an egg only slightly rises at one end, it should be fine to use in the next 24-48 hours.

However an egg that completely lifts off the bottom of the glass should be disposed of immediately.

Why does an egg float in water?

There are technically two reasons a rotten egg will float in water.

  1. Water vapour will slowly leave the egg through the porous shell, decreasing the mass of the egg. If the mass of the egg is less than the mass of the water displaced by the egg, it will float.
  2. Gases released as the egg begins to break down cause it to be more buoyant, meaning it floats.

Dozen eggs photo by observing life

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Comments 2 comments

cady 5 years ago

intersting


Wendy Butcher 2 years ago

Hi there can you answer this question,i collected my freshly laid eggs yesterday and did the water test today and they all floated,so i cracked them open and they were all ok nice bright and yellow and no rotten smell.So why on earth did they all float??

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