Why Do Eggs Float? How To Tell A Bad Egg

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Why Do Some Eggs Float? – Fresh Eggs vs. Old Egg

 

QUESTION:

If you have kept eggs past the use before date, try to boil them, and if most sink to the bottom of the pan and a few float on the water – should you throw out the floating eggs?   It has been a while since I was taught much about eggs and I do not remember any of my eggs ever floating.  If the floating eggs are not bad then why do they float?

 

QUESTION:

I sometimes notice that in a batch of six (6) or so chicken eggs that have finished hard-boiling, several will barely float to the surface.  All six are known to be average freshness for supermarket supplied eggs.  Upon peeling, careful inspection shows no abnormalities.  When eaten they taste fine.  Any idea what’s going on? A pretty thorough search of the WEB didn’t turn up any answer, so the information isn’t commonly known.


 

ANSWER: 

Learn All About Eggs and How To Cook Them.

Egg shells may seem pretty solid, but they are in fact slightly porous.

Old eggs float in fresh cold water because of a large air cell that forms as the egg cools after being laid.  As the egg ages, air enters the egg and the air cell becomes larger and this acts as a buoyancy aid.

Generally, fresh eggs will lie on the bottom of the bowl of water.

Eggs that tilt so that the large end is up are older, and eggs that float are rotten.  The tilting is caused by air pockets in the eggs that increase in size over time as fluid evaporates through the porous shell and oxygen and gases filter in.  The older an egg gets the more gas builds up inside it.  More gas = more floating!

Carefully lower your eggs into fresh cold water (do not use salted water) using a spoon:

Eggs and carton

If the egg stay at the bottom – it is fresh.

If the egg is at an angle on the bottom – it is still fresh and good to eat.

If the egg stands on its pointed end at the bottom  – it is still safe to eat but best used for baking and making hard-cooked eggs.

If the egg float – they’re stale and best discarded.

The final test:

To make sure the egg is not spoiled, break it into a clean bowl and check to make sure it doesn’t have a bad odor or appearance.

 


 

Comments from Readers:

Recently I was informed the way to tell if an egg was bad was to place it in water and see if it floats.  Because as the egg aged, gasses were created in the egg causing it to float.  Having more air in the egg makes the egg more buoyant.  I disagreed with this explanation but was pointed to your website which supported this explanation.  On your website under the question: “Why do some eggs float?” you state:

Egg shells may seem pretty solid, but they are in fact slightly porous.  Old eggs float in fresh cold water because of a large air cell that forms as the egg cools after being laid.  As the egg ages, air enters the egg and the air cell becomes larger and this acts as a buoyancy aid.

Generally, fresh eggs will lie on the bottom of the bowl of water.  Eggs that tilt so that the large end is up are older, and eggs that float are rotten. The tilting is caused by air pockets in the eggs that increase in size over time as fluid evaporates through the porous shell and oxygen and gases filter in.  The older an egg gets the more gas builds up inside it.  More gas = more floating!

I am glad to now know how to determine if an egg is bad or not, but I did want to set you (and your readers) straight on why egg floats.  You are partially correct, however, it is not the fact that air is getting into the egg that makes it float.  It is the fact that mass is leaving the egg.  Since the eggshell does not expand or contract, the density of the egg is only dependent on the mass of the egg (density equals mass divided by volume and the volume of the egg is constant).  If the egg weighs less than the amount of water displaced by the egg it will float.  If it weighs more, it will sink.  It does not make a difference if there is more or less air in the egg.  For example, if the inside matter (yolk and whites) were replaced with a steel ball of equal weight, there would be a lot of air in the egg.  But the overall weight of the egg would be the same (actually it would be slightly heavier since air does have a weight associated with it and now you would have more air in the egg) so the egg would still sink.  The reason why an egg floats is because as it decomposes, water vapor and gases are released through the porous shell.  This is what causes the yolk and whites to shrink which in turn makes the air cell larger.  Some ambient air enters the shell as the water vapor and decomposition gasses leave, but overall the mass of the egg is reduced.  More mass is going out of the shell than coming in through the shell.  More mass leaving = less weight = more floating!

Thank you – Rob Dyer

 

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Comments and Reviews

14 Responses to “Why Do Eggs Float? How To Tell A Bad Egg”

  1. Jane Doe

    I’ve raised chickens for the better part of 30 years now and up until recently always believed that a floating egg was a rotten one. However, it appears I have some Wyandottes who lay eggs with enormous air pockets in my current flock, because I have eggs that I know for a fact are only 2 weeks old (in the fridge the whole time) that float like fishing bobs. I marked a couple dozen to let age a few weeks so they’d be easier to peel since fresh eggs don’t peel for nothing (yes I’ve tried ALL the tricks). The others in the carton sank, but those light tan ones from the Wyandottes all floated. The same eggs, even if cracked the day they are laid, hit the skillet and bust all over the place. Forget about over easy with them, they might as well be pre-scrambled. I joke that those particular hens must fart right before the shell goes on and that’s why their eggs are all gassed up, ha, but honestly, no clue. The whole flock is 1-2 years old, they’re all free range, eating the same thing.

    Reply
    • Linda Stradley

      That is very interesting. As I have never raised chickens, I did not know about this. Thank you for sharing this with everyone.

      Reply
    • lee

      I also have wyandottes whose eggs float also when fresh.

      Reply
  2. Karen

    I tried my neighbors chicken eggs and didn’t eat them again because they tasted to gamey. So I eat organic store bought, Egglands Best. I recently put three in cold water and a small part of larger end floats. Should I not eat them?

    Reply
    • Linda Stradley

      I use fresh chicken eggs all the time myself.

      Carefully lower your eggs into fresh cold water (do not use salted water) using a spoon:

      If the egg stay at the bottom – it is fresh.

      If the egg is at an angle on the bottom – it is still fresh and good to eat.

      If the egg stands on its pointed end at the bottom – it is still safe to eat but best used for baking and making hard-cooked eggs.

      If the egg float – they’re stale and best discarded.

      The final test:

      To make sure the egg is not spoiled, break it into a clean bowl and check to make sure it doesn’t have a bad odor or appearance.

      Reply
  3. fakeagent

    Your style is unique in comparison to other people I have read stuff from. Many thanks for posting when you’ve got the opportunity, Guess I will just book mark this web site.

    Reply
  4. Libby Edwards

    So the real question is a floating egg good or bad? I’m a little confused I bought some fresh eggs from a farmer I had six white eggs had bought from the store, I bought two dozen of fresh brown eggs from a farmer ….my brown eggs floated…my white eggs sank to bottom. So are they good or are they

    Reply
    • Linda Stradley

      From everything I have learned from experts, if the egg float – they are stale and best discarded

      Reply
  5. Nancy Greenwood

    Some months ago I purchased eggs from the farmers’ market and got into a discussion about egg storage. She informed me that they do not wash their eggs so they don’t have to be refrigerated like store bought eggs. Even organic eggs have to be washed if sold commercially she said. Many countries don’t have refrigeration but they do eat eggs. Does it make a difference if eggs are unwashed so they still have the natural film of coating that nature provides? Thank you… I just boiled eggs that were floating which is why I was looking this up.

    Reply
    • Linda Stradley

      Yes, it makes a difference in the life of raw eggs. The lady at the Farmers’ Market is right.

      Reply
  6. Kathy Woodbury

    Put the eggs in cold water, if the egg sinks to the bottom, it is good. Some good eggs will float to the top, but it will be the narrower end of the egg that comes to the top — like those Wyandotte eggs. However, if the wide end of the egg floats to the top, the egg is ROTTEN. Myself, I wouldn’t try checking because they can explode and smell up your kitchen horribly. If you want to crack them, take them outside a good distance from your house.
    Check this out: https://www.youtube.com/watch?v=noqWANzo8r8

    Reply
  7. Myrtle Houston

    I have told many people about the same thing and I Seshan I am very happy to see it with other people I love to teach and I love cooking . Keep up the good work. Sincerely BOSS GG CHEF

    Reply
  8. Russell Palmer

    I find even if the eggs float, does not mean they are rotten. The best way to check is break one or two in a bowl. If they are rotten, you will immediately smell it. I have had some that float and when I checked them in a bowl, smelled fine. I fried them and they did not taste bad at all. I believe it is from the actual egg aging in the shell that causes them to float. I guarantee you will smell a rotten egg when you break it.

    Reply
  9. Jed

    Floating egg is bad is hogwash. I threw my floating eggs away then went back and checked half. All good. So I ate the other half.

    Reply

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