What is a Chicken Egg? A Complete Guide

A female chicken, called a hen, lays an egg, which is where babies are born. For thousands of years, it has been an important food source for people. This complete guide gives you an overview of chicken eggs, including how they are made, what they’re made of, and other important facts.

How Are Chicken Eggs Formed?

Chicken eggs begin their journey inside the hen’s ovary. The ovary holds small yolks inside structures called follicles. Once the yolk matures, the follicle ruptures and the yolk is released into the oviduct, which is a long, winding reproductive tube where the egg develops.

The egg stays in the infundibulum for about 15 minutes, which is the first part of the oviduct. If sperm is present, fertilization can happen there. After that, it goes into the magnum for three hours while the egg white proteins are added. The shell membranes are added over the course of an hour in the isthmus. Finally, the egg gets to the shell gland, where it takes a full day to form the hard calcium carbonate shell. When it’s done, it comes out of the hen’s vent. The entire process takes 24-26 hours.

Key Parts of a Chicken Egg

A chicken egg contains the following key structures:

• Shell: The hard outer covering made of calcium carbonate. It can be brown or white.

• Shell membranes – Two inner membranes that provide protection.

• Albumen (egg white) – The clear liquid that surrounds the yolk, made mostly of protein and water.

• Chalazae – White twisted strands that anchor the yolk.

• The yolk is the yellow part in the middle of the egg that has fat, protein, and vitamins that help the chick grow.

• Germinal disc – A small white spot on the yolk that contains the hen’s genetic material. In fertilized eggs, this becomes the embryo.

Differences Between Fertilized and Unfertilized Eggs

The key difference between fertilized and unfertilized chicken eggs is that fertilized eggs can develop into chicks, while unfertilized eggs cannot.

• Fertilized – Contain genetic material from a rooster and hen and can become chicks if incubated. Have a larger germinal disc.

• Unfertilized – Contain only the hen’s DNA and will never hatch. Lack a rooster’s contribution. Most eggs consumed are unfertilized.

Both fertilized and unfertilized eggs are edible. Only fertilized eggs that are incubated for 21 days can yield baby chicks.

Nutrition Facts

Chicken eggs are packed with nutrients and relatively low in calories. Here are some of the nutrients found in a large 56g egg:

• Calories: 72
• Protein: 6g
• Fat: 5g
• Vitamin A: 6% DV
• Vitamin B12: 9% DV
• Vitamin B2: 15% DV
• Phosphorus: 9% DV
• Selenium: 22% DV

The protein found in eggs contains all 9 essential amino acids, making eggs a complete protein food. The fat is mostly unsaturated fat, plus vitamins A, B12 and B2.

Cooking Chicken Eggs

Chicken eggs are very versatile in cooking. Here are some of the most common ways to cook them:

• Scrambled – Beat eggs and cook while stirring constantly. Often add milk, cheese or veggies.

• Fried – Cook eggs in a pan with butter or oil. Can be sunny side up, over easy or hard.

• Poached – Gently simmer eggs in water. Produces a soft, runny yolk.

• Boiled – Cook eggs in boiling water. Produces a firm, cooked yolk.

• Baked – Bake eggs in a muffin tin or ramekin. Great for making egg bites.

• Omelets – Cook eggs mixed with ingredients like cheese, meat or veggies. Folded over.

Egg Safety and Storage

To safely handle eggs:

• Refrigerate eggs after purchase and use within 3-5 weeks. The cold limits bacterial growth.

• Cook eggs thoroughly until yolks and whites are firm. This kills any bacteria present like Salmonella.

• Avoid consuming raw or undercooked eggs.

• Discard eggs that are cracked as this allows entry of bacteria.

• Wash hands and cooking tools after handling raw eggs to avoid cross-contamination.

Storing eggs pointy side down may also help preserve freshness longer by keeping the yolk centered.