With Easter this Sunday, I’ve been thinking about eggs. Eggs are common in Easter celebrations as a symbol of the resurrection. Christians believe that Christ rose from the tomb, and eggs are an appropriate symbol because new life emerges from them.
Eggs are a staple in the kitchen. There are numerous ways to prepare eggs: scrambled, sunny-side up, poached, boiled, etc. Eggs are a vital ingredient as well. They act as binding agents, emulsifiers, foaming agents, and thickeners.
The real secret to eggs lies in their anatomy. An egg is a complex little package, as shown in the diagram below.
Shell: the hard outer layer of the egg. A major component of the shell is calcium carbonate (CaCO3) which sits in a protein matrix. Shells are full of tiny pores which is how color gets onto the egg white of a dyed Easter egg.
Cuticle: a mucous coating around the shell which keeps out bacteria. Normally store bought eggs do not have the cuticle because it is removed when the eggs are washed. A thin layer of oil is put on to replace it.
Membranes: used to separate different parts of the egg, made primarily of keratin and mucin. The shell membrane sticks to the shell of the egg. The egg membrane is right inside the shell membrane but it clings to the egg. The egg membrane is the film that needs to be peel off a hard boiled egg. The vitelline membrane separates the egg yolk from the rest of the egg.
Air Cell: the space between the shell membrane and the egg membrane at the broad end of the egg. It gets larger as the egg ages.
Albumen: commonly known as the egg white, has three layers. The outer and inner layers are thin while the middle layer is thick. This is easy to see in sunny side up eggs.The main protein of egg white is albumin and has many uses in cooking.
Chalaza: helps to keep the egg yolk in the middle of the egg. There are two of them, one attached to each end of the egg. This is the stringy stuff that clings to the shell when an egg is cracked open and its contents are removed.
Yolk: contains the bulk of the nutrients for the egg; vitamin A, phosphorus, calcium, lipids, and more. It is primarily yellow but has a white center. The yolk changes color based on bird species and what the bird eats.
Germinal Disc: can develop into an embryo. Also called the germ, blastodisc, or blastoderm.
Other Fun Facts
The contents of an egg shrink over time. The air cell becomes larger, the thick white albumen layer decreases, and the yolk flattens. If an egg is really old you can hear the insides hitting the shell when you shake it.
The yolk of a boiled egg gets a greenish grey color when it is over cooked. This is a result of iron in the egg yolk reacting with hydrogen sulfide in the egg white which creates iron sulfide. This is not harmful at all, it just creates an unappetizing color.
To tell if an egg has been boiled, spin it. Boiled eggs will spin steadily because everything inside is solid. Raw eggs wobble as the contents shift a bit inside the shell.
There is so much more I could say about eggs, but it will have to wait for another post. Hope you have a happy Easter!
Feature Photo By: Maja
Source: Foods: A Scientific Approach (3 Edition) by Helen Charley and Connie Weaver