If you are new to poultry, you may think that candling eggs is no more than a 4-H science experiment. Or, maybe you have never heard of candling before. To a poultry operation candling eggs at regular intervals let’s you monitor the development of the embryo and can save you a few surprises down the road.

Candling eggs is not complicated. It takes a few supplies and only a few minutes. You need a dark room, a bright light, and the egg you intend to candle. The light we recommend is the Cool-Lite Tester created by GQF Manufacturing. This tool limits the time spent handling the egg, which reduces the chance of dropping or accidentally cracking its delicate shell. The simple design creates a tight seal against the base of the egg, decreasing the amount of light that escapes and gives you the best view of the inside of the egg.

Like we said, it’s not complicated but there is something to it. Let’s chat about the steps you need to take to properly and confidently candle your eggs.

Preparing to Candle Eggs

1. Consider the reasons why you are candling your eggs.

You candle your eggs to know which eggs are fertilized and how each embryo is developing. You do this by shining a bright light next to the egg and looking for specific features inside the shell. When it comes to your eggs, you should not expect a 100% hatch rate. Some eggs are never fertilized. These eggs are called “yolkers.” Some fertilized eggs stop developing during incubation; these are called “quitters.” The fertilized, properly developing eggs are called “winners.”

When you know you have a yolker or a quitter it is important to remove them from the incubator. If you don’t, the eggs will rot. During rotting the eggs will build up gas and if left in the humidity of the incubator, they can explode. Not only is this a smelly mess, it exposes the good eggs to bacteria from the rotted eggs. This leaves the embryos and later the chicks open to disease.

2. Gather the supplies you need to candle your eggs.

Like the name suggests, people use to candle eggs using an actual candle. They would place the egg next to a candle flame and inspect the inside of the egg from the light of the flame. Nowadays, you won’t need a candle; you need a very bright light that can create a tight seal on the outside of the egg. There are several different types of lighting tools you can purchase or make yourself, but we recommend the Cool-Lite Tester.

3. Establish the schedule to candle your eggs.

Most poultry producers will candle their eggs twice. The first time will be around 6-8 days after they are placed in the incubator. The first candling time will vary slightly based on the breed of eggs. Darker, brown eggs should be candled later than white eggs, as it is harder to see the early development against the dark shell. The second candling will occur about a week later. This candling will be used to identify any eggs that stopped developing or any you were unsure of during the first candling. Any eggs that you are still unsure of after the second candling, take note of and re-candle a couple days later. It’s best not to handle the eggs after 14 days.

Steps in Candling Eggs

1. Place the light on the egg.

When it comes to candling, you should do it in a completely dark room. If using the Cool-Lite Tester place the light on the larger end of the egg, which is where the air sac develops. Rotate it slightly until you have the best seal against the egg and the best view of the inside of the egg.

2. Identify the “winners.”

The winners are the eggs that have successfully developed into an embryo. To know if the egg is a winner look for a network of blood vessels that appear white. A dark outline at the center of the blood vessels is the embryo. You may even see the dark eyes of the embryo or the embryo moving slightly. These are both telltale signs that the egg is a winner.

3. Identify your “quitters.”

A quitter is an embryo that has stopped developing at some point during incubation. The main way to identify a quitter is by spotting the blood ring, a well-defined red circle visible on the inside of the shell. This ring develops after an embryo dies and the blood vessels pull away from the embryo and rest against the inside of the eggshell. You can also identify a quitter by dark red streaking inside the egg. However, the streaking can be mistaken in a healthy embryo, so it is best to identify a quitter with the blood ring.

4. Identify the “yolkers.”

Yolkers are eggs that will never develop into embryos because they were not fertilized. When you candle a yolker it will appear quite clear without any signs of development. It will glow. There will be no blood vessels, no dark embryo, and no blood ring. It will look the same way it did when you candled your eggs prior to placing them in the incubator.

5. Toss out the “yolkers” and the “quitters.”

When you are certain an egg is a yolker or a quitter, do not put it back into the incubator; you don’t want to give it a chance to rot. If you are uncertain, place it back in the incubator and check it again at day 14. If there are still no signs of development, toss the egg out.

Let us know what you think

Candling is an important process, especially to avoid the stinky surprise of an exploded egg in your incubator. Follow these steps and your incubator will remain clean…well as clean as a warm, humid environment full of eggs can possibly be.

Have you ever had an egg explode in your incubator? What are your best tips and tricks to candling eggs? Let us know in the comments!

If you are interested in the light featured in this article, check out the Cool-Lite Tester on our website.