Besides allowing our chickens to live outside, eat grass and certified organic grains to produce quality eggs, we also clean and candle our eggs. Candling is the process of using a very bright light to look at the interior quality of an egg and to check for cracks. I look for what are called meat and blood spots. These are both naturally occurring defects in eggs that don't normally effect the usability of the eggs, but just don't look appetizing. They are NOT developing chicks. Eggs must be incubated at 87 degrees for a period of time before any chick development happens. Eggs with cracks are fed to the dogs. (Our dogs are spoiled, unsellable eggs are hard boiled and fed to the dogs.)
We clean our eggs using an organic (OMRI approved) egg wash. Our eggs are laid in nest boxes that are cleaned and re bedded frequently. Occasionally the eggs will need to be cleaned because of dirt being tracked in on the hens feet and other materials the end up on the eggs. Excessively dirty eggs are not cleaned and are fed to the dogs. Sometimes the nest box material will get wet and stain an egg shell. Small stains from nesting material are green or yellow due to the chlorophyll in the hay we use. Any eggs with large stains are kept for use by us or fed to the dogs. Eggs are gathered daily and refrigerated.
Below: Example of candling. This egg has a hairline crack, indicated by the bright line.
Yolk color is influenced by the diet of the hen. Greens give the yolks a rich, golden color. Notice that the whites even take on a yellow color.
Anatomy of an egg: