Candling Eggs

You've got your eggs collected and you're buzzing with excitement about the little peepers that'll soon be joining your flock. But before we get too excited for the fluffy butt chick stage, there's a crucial step we can't skip: candling those eggs.

Candling is basically peeking inside the shells without cracking them open. It's a vital check-up on the health and development of your hatch, and the steps apply whether you're using an incubator or a broody hen!

I remember the first time I tried to candle eggs, squinting in the dark, holding an egg awkwardly over a flashlight, jostling with my kids for prime viewing, and thinking, “Am I doing this right?” Spoiler alert: I was..n't really.

But don’t worry, I’ve come a long way since then, and I’m here to share all the tips and tricks that’ll make you a pro in no time.

Jump to:

• Candling 101
• Why Candle
• How To Candle
• When To Candle
• Candling Dark Shelled Eggs
• Thoughts From The Chicken Coop
• Comments

Candling 101

Now, if you're picturing yourself holding a candle up to an egg like some sort of 18th century poultry lover, let me stop you right there, it's 2024! While historically, eggs were quite literally candled, we have the luxury of flashlights to make our jobs a LOT easier!

Shining a bright light through the egg allows us to "see through" the shell and monitor both the development of the embryo within the egg and the size of the air sac. Tracking development helps us to cull any eggs that either don't qualify for incubation or continued incubation.

While candling should be done with a careful hand, it does not hurt your eggs, but it should be done relatively quickly. Even in nature, despite the persistence of every broody hen I've ever met, they still need to get up off their clutch of eggs to eat, drink, and use the bathroom at least once a day. That said, it's important to try and keep your session to 30 minutes or less.

Why Candle

Candling is an important part of hatch management. This step helps to weed out infertile eggs, eggs that haven't developed, or eggs that stopped developing.

By inspecting eggs prior to incubation, we can ensure that only the most likely to hatch eggs occupy valuable incubating space. Monitoring eggs during the incubation process ensures that only viable eggs continue through the process.

The warm humid environment in an incubator or under your hen is a bacteria propagation playground. Cracked eggs or eggs that have stopped developing are susceptible to bacteria infiltration and rotting.

Failure to remove flawed eggs can lead to disastrous effects, on your hatch and yourself.

How To Candle

Way, way back in the day, chicken keepers would literally use candles placed in a wooden box with a hole cut in the top to inspect their eggs, luckily for us, we have handheld flashlights. Not only are they easier to work with, flashlights are also safer for the eggs, as they don't produce as much heat.

You can purchase specially made egg candling lights in both plug in version or battery powered, but any small flashlight should work. Some incubators even have built in flashlights, like my Nurture Right 360!

If you don't have a small flashlight, you can cut a piece of cardboard to fit over the lens of a larger one with a half to three quarter inch hole in it. This will help direct the light straight into the egg instead of escaping around the outside of the shell, making it easier to see what's going on in there.

The steps for candling are the same no matter which point in the incubation process you choose to do it:

1. Transport the eggs to a dark room. I like to use our windowless bathroom, the absolute darkness makes it much easier to see the dainty features inside the eggs.
2. Place the candling light over the fat end of the egg. This will shine light through the air sac and into the contents. Sometimes I hold my eggs pointy side up with the light at the bottom and sometimes I hold them pointy side down with the light at the top. Sometimes I do both, and sometimes I use 2 lights!
3. Rotate the egg 360 degrees on the light to ensure you've seen all the way round.
4. Carry on with your incubating plans!

When To Candle

There are 3 major benchmarks in the hatching/ incubating process.

Before Incubating:

All eggs should be candled before incubation, even if you've properly collected eggs for hatching, they should be candled again.

Looking For:

This first candling is primarily designed to weed out:

• Hairline cracks
• Double yolkers

Any eggs with hairline cracks are prime candidates for bacterial infection. If bacteria enters the egg at the beginning of the incubation process, it is likely to rot the egg. If an egg goes through the entire incubation period of 21 days and it's been compromised, it may literally explode.

Any egg that explodes due to bacterial rot can contaminate other eggs within the incubator and even your incubator itself. Not to mention, the smell. Oh my God, if you've ever cracked open a greenish black rotten egg, and gagged yourself hoarse, you know what I mean! HA!

We're also culling any double yolker eggs. Double yolks are unlikely to hatch because space and resources within the egg are limited. Chicks need to rotate into a specific position with their beak under their right wing in order to hatch, and this is exceedingly difficult to do with two chicks in tight space.

Day 7:

One week into the incubation period, we can determine the difference between viable or fertile eggs and unviable/infertile eggs.

Looking For:

This inspection is designed to identify development within the eggs. By day 7, there are 3 possible outcomes:

1. Web of vessels around the egg = developing egg
2. Thin ring or blood ring around the egg = development started and halted. Embryo has died
3. No change from day 1 = egg is infertile and did not develop.

All eggs that fit into category 1 should be returned to the incubator.

Any eggs in categories 2 or 3 should be discarded - either tossed in the trash or compost heap, but do not feed these eggs to your animals as they can have high bacteria loads and cause illness in your animals.

If you are unsure of the progress in your egg, it's ok to put it back into the incubator again and check again on day 14. This can happen when you're new to candling, or when trying to candle dark shelled or speckled eggs. Whenever I'm unsure about an egg and put it back into the incubator, I make a small mark on the egg with a pencil so I can give it an extra close look on day 14.

The white egg in the photo below shows developing blood vessels while the green egg demonstrates no change. The white egg will be returned to the incubator while the green egg will be discarded.

Day 14:

At this point, we are looking for continued signs of development or signs of loss. By day 14, there are only 2 outcomes for your eggs:

1. Dark shadow except in the air sac, movement may be visible = viable egg with growing embryo
2. Murky contents and jagged air sac = embryo has died

Most embryos stop developing between days 6 and 14, so checking one and two weeks into the incubation process can help remove the undeveloped eggs, keeping the incubator fully of healthy eggs that are more likely to hatch and thrive.

It is important to remove eggs that have stopped developing or haven't developed at all because they can cause you issues in your incubator.

The white egg below shows well developed blood vessels and an obvious embryo, one that actually moved under inspection. The brown egg demonstrates the murky contents and blood ring - these are hallmark signs that the embryo has stopped developing.

Candling Dark Shelled Eggs

Working with dark shelled eggs takes a keen eye, and an ultra bright light to even stand a chance. Marans, Welsummer, and other dark brown or speckled eggs are incredibly difficult to candle for a newbie.

I recommend a very dark room and starting with white or light shelled eggs first, then moving to progressively darker eggs within your clutch, this can help you to identify different features within the eggs and familiarize yourself with what you're looking for before playing on expert mode!

Sometimes it helps to use two candling flashlights, especially with Marans eggs. Our Marans lay such dark eggs with thick shells, there's almost no candling happening. So when it comes to them, I often use the built in candler on my incubator and the secondary hand held candler I have.

Don't be afraid to mark the eggs and put them back into the incubator if you're unsure at day 7.

The eggs below, Welsummer and Marans, respectively, are candled on day 7. I can't tell enough to keep or toss at this point, so I returned them to the incubator for further inspection.

Thoughts From The Chicken Coop

Candling eggs is a critical step in the incubation process, offering a window inside of your eggs. It allows you to intervene early, removing eggs that won't hatch and thereby preventing potential problems.

These few moments set aside for monitoring ensures that your incubator remains a clean, viable environment for the development of healthy chicks!

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Sources

Story's Guide To Raising Chickens

Nebraska Extension

Incubator Warehouse