How to tell whether an egg is bad both before and after cracking it?
rpautrey2
How can I tell whether an egg is bad both before and after cracking
it?
In general, appearance is not the best way to measure the safety of
eggs. We don't recommend using appearance alone as your egg safety
test. Particularly with respect to an egg that has been cracked open,
there can be a number of discolorations in the white or yolk, which do
not represent food safety concerns. However, with that in mind, there
are certain types of egg inspection that also make sense when trying
to determine whether an egg has gone bad or not.
First, we would look to ensure that there are no cracks in the shell.
If there are cracks, then we would dispose of the egg.
Once you have cracked the shell, smell the egg. If it does not smell
good, we would throw it away. If the raw white of the egg has turned
pinkish, green, or black, you should also definitely toss out the
egg.
In terms of determining quality from an uncracked egg, in his classic
book "On Food and Cooking," Harold McGee discusses how better quality
eggs have smaller air cells; he notes that in a fresh egg, the space
is about 1/8-inch deep and has the diameter of a dime. To test the
size without cracking it, he writes that you should put the whole egg
in a bowl of water; if the air cell is much larger than the size noted
above, the wide end of the egg will rise above the narrow end. If your
egg does this, it would then be a reflection that it is not that
fresh.
McGee's freshness test is also related to a long-time folklore belief
about the degree to which an egg will float in water. According to
this belief, a spoiled egg will float all the way up to the surface,
but a safe egg will not. While this belief is not completely accurate,
it does harbor one important element of truth. If the pores in an
eggshell have become sufficiently large, or if the shell has been
cracked, it is possible not only for air but also for additional
bacteria to enter into the egg, become metabolically active, and
create gas inside the eggshell. This additional gas could cause the
egg to do more floating. (However, other factors could also cause the
egg to float, including simple transfer of air through larger pores,
even if no bacteria had migrated into the egg.)
The bottom line: while you may want to try the float test for fun, or
the "wide end up" float test for freshness, judge by the smell and
discoloration of the opened egg as described above, or notice if there
are cracks in the shell of the unopened egg, when determining its
safety.
For more information on this topic, please see:
Eggs
© 2001-2008 The George Mateljan Foundation