What is Egg Candling? The Ultimate Guide

Egg candling is an easy and harmless way to monitor signs of development in eggs. After a few days of incubation, shining a bright light on a poultry egg can reveal what’s going on inside it. Candling eggs lets chicken owners maximize the chances of successful hatching. It also reduces the risk of exploding eggs or cracked eggs in the incubator.

Candled Incubated egg

The goal of candling chicken eggs is to remove infertile or rotten eggs—called non-viable eggs—and keep fertile or viable eggs. This process allows the incubation process to be successful and results in hatched healthy chicks.

This article is a complete guide on how to candle eggs. In addition, you will learn about ways to ensure that the incubation process and hatching eggs are successful.

What Is Candling and How Do You Do It

Candling eggs involves holding a strong light to an egg to observe embryonic development. The light penetrates the eggshell, letting you detect the network of blood vessels, blood spots, meat spots, and movement. Egg candling also enables you to see if there are cracks in eggshells.

To candle eggs, you need to be in a darkened room and have an egg candler. If you don’t have a candling torch, a bright flashlight with LED lamps is fine. First, place the larger end of the egg at the light. Then, rotate the egg to look for signs of a healthy embryo.

The goal of egg candling is to improve hatch rates. By removing eggs with dead embryos, you ensure that only healthy eggs are kept during the incubation period.

When to Candle Chicken Eggs

The first time to candle an egg is just before you put it into the incubator. You want to check for hairline cracks and discard those. The second time to candle is on day seven. Then on day 14, you can check the eggs for the last time.

Egg candling is a harmless process to identify good and rotten eggs.

The best time to start checking eggs in an incubator with a candler is after a week of incubation. During the first few days, it’s almost impossible to see anything. Additionally, waiting until the seventh day of incubation prevents damage to the developing embryo.

During the incubation period, you can check eggs daily—but this is not advisable. Although embryos constantly develop, it’s not possible to see noticeable daily changes. So, the next time to candle chicken and poultry eggs is after 14 days incubation.

Most poultry eggs have a 21-day incubation period. So, it’s advisable to avoid checking eggs during the last few incubation days, as this is when the chick gets into the hatching position.

How to Candle Chicken Eggs

When you have your egg candling equipment ready, you are prepared to check the health of eggs in your incubator. Here are the steps you need to take to see what’s going on inside the egg.

  • Put the candling equipment near the incubator.
  • Ensure the room is as dark as possible—pitch black is best.
  • Place the wide, rounded end of the egg against the light—this is where the air sac is located.
  • Gently move the egg from side to side and rotate it to examine the egg.
  • Try not to have the egg any longer than 20 to 30 minutes outside the incubator.
  • When you have finished, number the egg with a pencil so you can record your findings. This allows you to compare development at seven days and 14 days.

What To Look for When Egg Candling

Eggs with healthy embryos are called winners, whereas dead embryos are called quitters. So how can you tell the difference between an infertile yolk and one that will develop into a chick?

How to Spot Healthy Embryos

During the incubation process, you should notice signs of embryo development from day seven.

Here is what to look for in a healthy embryo:

  • Fertile eggs will have a dark spot which is the embryo.
  • Look for spider-like veins that create a patterned web of veins.
  • Rotate the egg to get the best views.
  • You may also notice a tiny heart beating or the embryo moving.
  • The two darkest spots in the embryo are the eyes.
  • When candling eggs on day 14, the embryo should take up two-thirds of the egg.

How to Spot Dead Embryos

Embryos can stop developing during incubation. That can happen even though the humidity level and incubator temperature are at optimal levels.

Here is how to spot a bad egg or quitter:

  • There is a noticeable well-defined red circle called a blood ring on the shell’s inside.
  • You’ll notice blood spots or blood streaks.

It’s good to remember that the dark blood spots are easy to mistake for the embryo. So, the sign of a blood ring is usually the best way to spot the quitters in the incubator. You should discard all eggs showing signs of embryo death.

Signs of Non-Fertile Embryos

Some eggs don’t get fertilized and won’t develop into embryos. These eggs are called yolkers. If an egg is a yolker, you will not see a dark embryo, blood vessels, or a blood ring.

Different Types of Candlers

All egg candlers consist of a bright incandescent or LED light that illuminates the egg’s inside. When choosing a bright light for candling, the most crucial factor is to ensure it doesn’t produce heat, which could damage the embryo.

An egg chandler isn’t an expensive accessory if you keep chickens. And it’s vital to buy one to increase successful chick hatching. So what are your options if you want to start candling eggs?

A basic candler looks just like a flashlight. The lamp end is specially designed to allow you to place an egg on the candler. It’s also a good idea to look for a candler with a bright light to check dark and light eggs. Additionally, a candler light with different size covers enables you to check large and small eggs.

Another type of candler is one that sits nicely on flat surfaces—thus reducing the chance of breaking an egg. The best and most expensive egg viewers rotate the eggs and have a magnifying lens and connectivity to webcams.

Before buying an egg candler, make sure that it’s designed for the type of eggs you have. For example, some cheaper egg viewers only work on plain and light-colored eggs. If your birds produce dark or spotted eggs, then choose a suitable device.

FAQs — Reasons for Candling

Does candling tell you if an egg is fertile before incubation?

Candling helps you know if an egg is fertile after a few days of incubation. Usually, by day four, the egg candler will show a dark spot around the middle of the egg. You should also see some spider veins developing. With a non-fertile egg, you will only see the outline of the yolk without any veining.

Does candling damage the egg?

Candling is a safe way to check the health of eggs in an incubator. But you need to handle the eggs carefully, not expose them to cold temperatures, or leave them out of the incubator for too long. Generally, it is safe to remove incubating eggs for candling.

How long is it safe to have the egg out of the incubator?

Although incubating eggs can be out of the incubator for up to 30 minutes, it’s best to keep the time to a minimum. Try to limit candling time to ten minutes. If you have many eggs, then only candle a few at a time.

How do I mark eggs after candling?

Use a regular pencil to mark eggs with a number after candling. Don’t use a marker because the toxins can leech through the shell and affect embryo development. You can record the air sac size, breed, and color on the shell for each numbered egg.  

What do I do if my eggs become rotten?

It’s vital to remove rotten eggs from incubators as soon as you suspect the embryo has died and has started to rot. Eggs become rotten if bacteria get into the egg. Gasses develop and turn the yolk and albumin into a putrid liquid. It’s not uncommon for rotten eggs to start oozing liquid or explode in the incubator.

To prevent rotten eggs, don’t put dirty or soiled eggs into the incubator.

What are the dangers of shining a bright light on an egg?

There are no dangers to shining a bright light to view the developing embryo. As long as you don’t keep the egg out of the incubator for too long and the flashlight isn’t hot, there is no risk of embryo damage.