Why Do Some Eggs Float? - Fresh Eggs vs. Old Eggs
 

carton of eggsQUESTION:

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: 
Click here to Learn All About Eggs & 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:

  • 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.

Did you Know - Eggs from your own hens (farm raised) are like homegrown vine-ripened tomatoes. Better that anything that comes from the supermarket.