Your chicken coops are ready, your nest boxes are prepared, and your chickens are laying. Congratulations! Your backyard flock is off to a great start. What’s next? 

If you’ve never heard of egg candling, you might think it’s not necessary for your hens. However, candling eggs at regular intervals 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. 

Candling eggs lets you know which eggs are fertilized and how potential embryos are developing.

Not every egg hatches. Average hatch rates are typically around 75%. “Yolkers” are eggs that are never fertilized. “Quitters” are fertilized eggs that stop developing during incubation. Finally, fertilized, properly developing eggs are “winners”.Knowing when you have a yoker or a quitter is important. If not removed from the incubator, these eggs can start to rot.

As they rot, eggs build up gas and can explode. Not only is this a smelly mess, but it also exposes the good eggs to bacteria from the rotted eggs. This leaves the embryos and later the chicks open to disease.

As the name suggests, people used to candle chicken eggs using an actual candle. They would put the egg by a candle and look inside it using the light from the flame. Later, farmers would candle eggs using a bare light bulb or even a flashlight.

These days, you can buy or make many lighting tools, but we recommend the Cool-Lite Tester from GQF Manufacturing.

The Cool-Lite Tester helps reduce the risk of dropping or cracking the delicate eggshell by minimizing handling time. The simple design creates a tight seal against the base of the egg, decreasing the amount of light that escapes and giving you the best view of the inside of the egg.

Typically, eggs should be candled up to three times. It’s tempting to want to take a peek more often, but it should be avoided. Frequently opening the incubator and removing eggs can cause temperature fluctuations that are harmful to the embryos.

It’s a good idea to candle your eggs before placing them in the incubator. This will help you establish a baseline to compare against later. You should also look for cracks in the shell. These cracks can allow bacteria to enter the egg, resulting in the death of the embryo.

The next candling takes place 6-8 days after they are placed in the incubator. The first candling time will vary slightly based on the breed of eggs. Brown eggs need to be checked for development later than white eggs. This is because it is more difficult to see inside the dark shell.

The final candling takes place about a week later. This candling is used to identify any eggs that stopped developing or any you were unsure of during the first candling. If you're not sure about any eggs after the second check, take note and check again in a few days. It’s best not to handle the eggs after 14 days

Before you start, wash your hands. This minimizes the risk that you will transfer bacteria to the eggs. You should candle in a completely dark or very dimly lit room. Remove the eggs one at a time, not all at once. Work quickly. The egg should be out of the incubator for no longer than 5-10 minutes.

Place the light on the egg. 
If using the Cool-Lite Tester or other similar light, put the light on the bigger end of the egg where the air sac forms. Rotate it slightly until you have the best seal against the egg and the best view of the inside of the egg.

Identify the “winners.” 
You’ll know an egg is a winner if you can see 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.

Identify your “quitters.”
To find a quitter, look for the well-defined red circle on the inside of the shell called the blood ring.

The blood ring is formed when an embryo dies. The blood vessels of the embryo separate from it and rest against the inside of the eggshell. You can also identify a quitter by the dark red streaking inside the egg. But streaking can be confused in a healthy embryo, so it's better to find a quitter using the blood ring.

Identify the “yolkers.”
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.

Remove the “yolkers” & the “quitters.”
Yolkers and quitters should not be returned to the incubator, where they will rot. If you’re not sure, place the egg back in the incubator and recheck it on day 14. If there are still no signs of development, toss the egg out.

Candling is an important process, especially to avoid the stinky surprise of an exploded egg in your incubator. Hatching chicks successfully is a rewarding experience - and a very cute one!

You’ll find the Cool-Lite Tester, as well as incubators, feeders, waterers, and more in our poultry products section.

For expert help choosing an incubator or other poultry products, give us a call at 888.433.5275.

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