Science Fair question about eggs going bad

That's not an easy question. Eggs go bad because bacteria gets inside and multiplies. With a washed egg the bacteria has an easier time to get in, but it has to be present outside the egg to start with. Temperature plays a part too. Bacteria will grow a lot faster at 100 degrees Fahrenheit than at 70 degrees.

Just because an egg floats doesn't mean it's bad. As they age, eggs lose moisture through the porous shell. How fast they lose moistue depends on the humidity of the air. The drier the air the faster it loses moisture. At some point it loses enough mositure to stand on end instead of laying flat. The pointy side will be down and the air cel will be up. Eventually it loses enough moisture to actually float to the surface. I really don't know if washing the bloom off affects how fast it loses moisture. But maybe you could look at it standing in end in water instead of actually floating to the surface?

If bacteria gets inside and multiplies that can generate gasses inside the egg. That can cause it to float too. So the float test doesn't really tell you which ones are bad, just which ones to be really suspicious of.

Mother Earth News had an article about storing eggs in different conditions but I lost that link when my computer crashed. Best I remember the eggs lasted a really long time just on the counter. That study did not addressed washed versus unwashed but looked at egg quality as much as whether it got infected with bacteria. THey really do last a long time.

 

Here's the article Ridgerunner was talking about. http://www.motherearthnews.com/Sustainable-Farming/1977-11-01/Fresh-Eggs.aspx

We've eaten washed eggs that floated. They were fine, if old. Floating just isn't a sure sign of decay in eggs, since normal aging will cause enlarged air sacs and floating.

Unfortunately, I don't think that your eggs will go bad in time for the science project.