Image via Wikipedia
From the Hobbit:
Riddle: A box without hinges, key, or lid,
Yet golden treasure inside is hid.
Answer: An egg.
Most of us who have chosen to live our lives under the banner of "Paleo" consume eggs. And why not? Eggs have been eaten by mankind for millennia. Bird eggs (including chicken and turkey eggs) consist of a protective eggshell, albumen (egg white), and vitellus (egg yolk), contained within various thin membranes. Every part of an egg is edible,although the eggshell is generally discarded. Roe and caviar are edible eggs produced by fish, but this post is about eggs from birds.
The largest concern over eggs is how to tell if they are fresh or not.
Assuming the eggs have been bought when they were very fresh, they will last 30-40 days in a refrigerator. The best way to tell if an egg is still fresh, meaning edible, is to crack it open. Very fresh eggs tend to have a loose, light yolk and a clear white. The thick, whitish strings that attach the yolk to the white, called the chalazae, will be very prominent in a fresh egg. As the egg ages, the chalazae will slacken, the yolk gets darker and tougher, and the white becomes dingy. Even then, these eggs are still safe to use. A rotten egg, however, is immediately recognizable, as the smell is powerfully offensive.