Jason Bradwell's 365/366 Photo a Day Blog

An egg is a round or oval body laid by the female of many animals, consisting of an ovum surrounded by layers of membranes and an outer casing, which acts to nourish and protect a developing embryo and its nutrient reserves. Most edible eggs, including bird eggs and turtle eggs, consist of a protective, oval eggshell, the albumen (egg white), the vitellus (egg yolk), and various thin membranes. Every part is edible, although the eggshell is generally discarded. Nutritionally, eggs are considered a good source of protein and choline.

The yolk in a newly laid egg is round and firm. As the yolk ages it absorbs water from the albumen which increases its size and causes it to stretch and weaken the vitelline membrane (the clear casing enclosing the yolk). The resulting effect is a flattened and enlarged yolk shape.

Yolk color is dependent on the diet of the hen; if the diet contains yellow/orange plant pigments, then they are deposited in the yolk, coloring it. A colorless diet can produce an almost colorless yolk. Farmers may enhance yolk color with artificial pigments, or with natural supplements rich in lutein (marigold petals are a popular choice), but in most locations, this activity is forbidden.