Incubating chicken eggs is exciting and being able to monitor the growth of a chick embryo allows us to become more involved in the whole process. By knowing how to properly candle chicken eggs it not only allows us to follow a chicks embryonic development, but it can increase the hatch rate as well!
What is Egg Candling?
Egg candling is a common practice when incubating chicken eggs and involves the process of shining a bright light through an egg to check the viability and monitor the embryonic development and weight loss of the egg. It is usually done at certain times during embryonic development in a dark room.
Egg candling is best done in a dark room so it is easier to see the outline of tiny blood vessels and later on during the development, be able to see a chick embryo moving around inside of the egg.
A long time ago, farmers used to check the embryonic development by holding the egg up to a candle. This is how the term “candling” came about!
What is the Purpose of Candling Eggs?
Candling allows us to monitor embryonic development and discard any eggs that are unviable, decreasing the chances of it exploding and contaminating the rest of the eggs. It also allows us to monitor the growth of the embryo by keeping track of the air sac at the top of the egg.
During normal embryonic development, it is expected that the air sac gradually increase in size. This happens as the egg loses moisture through the pores of the egg. See the chart below for details.
If the size of the air sac is off, this is a signal to you that you need to either increase or decrease the humidity in the incubator. Too small of an air sac means the humidity has been too high and you need to lower your incubator humidity level. If the air sac is too large, the humidity level is too low in the incubator and must be raised.
| AIR SAC | PROBLEM | SOLUTION |
|---|---|---|
| AIR SAC TOO SMALL | HUMIDITY IS TOO HIGH | DECREASE HUMIDITY |
| AIR SAC TOO BIG | HUMIDITY IS TOO LOW | INCREASE HUMIDITY |
For more information on incubating chicken eggs read my article, 27 Clever Chicken Egg Incubation Tips for a Successful Hatch
Tip #1: Always Wash Your Hands Before Candling Chicken Eggs
Our hands carry all kinds of invisible bacteria that can be transferred to an egg during the candling process. It is essential to remember to wash your hands every time before you candle eggs. Wash your hands with warm, soapy water and vigorously lather the soap, scrubbing your hands for 30 seconds. Studies have shown that this will kill almost all bacteria.
Eggs are very porous. So if they are touched with dirty hands, bacteria can very easily be absorbed through the shell, contaminating the egg. You wouldn’t know this right away, but as days go on during the incubation process, bacteria will grow, often killing the embryo.
Incubators are breeding grounds for bacteria. Bacteria thrives in moist, warm environments and an incubator is just that!
Washing your hands also removes oils. Oils from your hands can clog the pores of an egg, decreasing the effectiveness of oxygen transfer during embryonic development.
Tip #2: Sanitize Flashlight Before Candling Chicken Eggs
Just as you should wash your hands before candling an egg, anything else that comes into contact with the eggs should be sanitized as well.
I keep a pack of sanitizing wipes next to my candling light and wipe the flashlight down each time prior to candling.
Tip #3: Don’t Wash Eggs Prior to Incubating or Candling
Eggs have a natural protective coating called a “bloom” or “cuticle.” Washing eggs prior to incubation will remove this protective coating, leaving the egg at risk of becoming contaminated at some time during the incubation process. Contaminated eggs can explode inside an incubator, spreading bacteria throughout.
During the last hour and a half of egg development inside of a hen, a bloom is deposited on the surface of the egg. This protects it by sealing the pores, preventing bacteria from getting inside. It also helps to regulate the moisture loss during incubation.
When a hen first lays the egg it is wet, but quickly dries. This is the natural bloom that will protect the egg from bacteria entering through its pores and contaminating it.
Even though eggs may have dirt on them, it is best not to wash them because it will wash the protective coating or “bloom” from the surface as well.
Washing eggs can also bring any bacteria that is already on the surface into the egg, especially if washed with cool water. If you must wash an egg, it is best to wash it with warm water, 90 degrees.
Cold water on a warm egg will cause the contents of the egg to contract, pulling the contents on the outside of the egg in, predisposing it to becoming contaminated.
Tip #4: Candle in Proper Room Temperature
Pick a location to candle your eggs that is neither too hot or too cold. Taking a warm egg out of an incubator that is 99.5 degrees and exposing it to freezing temperatures (and visa versa) can cause the egg to sweat. An egg that begins sweating is prone to becoming contaminated because it weakens the eggs natural protective coating, allowing microbes to make their way through the pores and into the egg.
This is the same reason why the FDA recommends you should use eggs for cooking within 2 hours of removing them from the refrigerator. For more information on how to store your eggs before using for cooking read my article, 9 Important Facts: How Long Are Chicken Eggs Good For?
Tip #5: Prepare a Dark Room With Supplies Before Bringing Chicken Eggs in to Candle
Designate a room that you will be doing your egg candling in, preferably a dark room. Keep all of your supplies in the same room and have them ready for candling before you bring the tray of eggs in.
| NECESSARY SUPPLIES | USE |
|---|---|
| CANDLER/FLASHLIGHT | USED TO SHINE THROUGH EGG TO ILLUMINATE DEVELOPING EMBRYO AND BLOOD VESSELS |
| DARK ROOM | EASIER TO SEE INSIDE EGG DURING CANDLING |
| SANITIZING WIPES | WIPE DOWN CANDLER/FLASHLIGHT |
| CLEAN TOWEL | LAY EGGS AND/OR EGG TRAY ON |
| PENCIL | MARK EGG SAC |
| PAPER | DOCUMENT DEVELOPMENT OF EACH EGG/ JOT NOTES DOWN |
The less time eggs are out of the incubator, the better. This is why it is a good idea to be prepared with all of the essential candling supplies in a dark room prior to taking the eggs out of their nice warm environment.
Tip #6: Choose a Time to Candle When You Are Not Rushed
By choosing a time to candle eggs that you are not rushed, you are more likely to follow all the proper steps of candling. You will be less likely to accidentally drop an egg and more likely to accurately document the development of the chick embryo.
All it takes is one time forgetting to wash your hands to transfer bacteria to the fertile eggs.
It is easy to accidentally drop an egg and this is more likely to happen if you are rushing through the process. Take your time. There is nothing worse than accidentally dropping and cracking a 14 day old viable egg.
Tip #7: Don’t Candle Too Often: Only Candle on Designated Days
Is Candling Bad for Eggs?
Candling does not harm eggs in any way. Mama hen will leave her clutch of eggs to poop, eat and drink for about 10 minutes each day. So it is ok to remove the eggs to candle, in proper conditions, to check on the embryonic development. It is best to only candle on designated days: 1, 7, 10, 14 and 18 to limit the chances of transmitting bacteria or dropping the eggs.
Some people choose to candle more often and others less. I think that the most important days to candle are on day 1, prior to incubation to either discard or give special care to eggs with fine cracks or detached air cells and again on day 14, so you can discard any “quitters.”
How Often Do You Candle Chicken Eggs?
Day 1: Check for fine cracks and for detached air cells.
Day 7: Check for blood vessel development. By this time you should see tiny blood vessels in viable lighter colored eggs. It may still be difficult to tell in dark brown and green eggs.
Day 10: This is when it is exciting to candle your eggs. Multiple blood vessels are very prominent now. In lighter colored eggs you should be able to see a big black spot in the egg. This is the eye! There is still a lot of room inside the egg and you should be able to see the embryo move around quite a bit. By this time you should be able to tell if there is any growth in the darker colored eggs. Discard any eggs that never started developing or are “quitters.”
Day 14: By this time you can see if there are any more “quitters.” Any eggs that have stopped developing will often have a “ring of death.” This happens when the blood vessels pull away from the embryo and float towards the air sac. Discard any eggs that stopped developing at this time.
Day 18 (Lockdown): This is the last day to take advantage of being able to candle. You are already having to handle them to remove the auto turner and to lay the eggs flat, so might as well candle them. At this time the chick embryo is taking up most of the egg, but in lighter eggs you can oftentimes still see if there is a ring of death or blood ring.
Tip #8: Mark Air Cell of Chicken Egg With a Pencil
Each time you candle, take the opportunity to mark the air cell on the egg. This way you can keep track of the growth of the embryo. In normally developing embryos, the air sac should gradually increase in size. Depending upon your findings, you may need to either raise or lower the humidity level in your incubator.
Keep in mind that it will be easier to mark the air cell or air sac on lighter colored eggs. Dark brown and green eggs are more difficult to candle because it is much more difficult to make out the embryo or blood vessels through the darker shells.
For the darker colored eggs, it is easier to tell that the egg is developing closer to 10-14 days.
Tip #9: Dispose of “Quitter” and “Yolker” Chicken Eggs
What are “Winners?” Winners are eggs that are showing embryonic development.
What are “Quitters?” Quitters are eggs that were once showing embryonic development, but have stopped developing for some reason. Quitters are often evident by the “ring of death,” when the blood vessels that were once connected to the embryo begin to decompose, detaching from the embryo and floating on the surface of the egg closest the air sac.
What are “Yolkers?” Yolkers are eggs that were never fertilized or eggs that never started developing.
Why do You Dispose of Quitters and Yolkers? It is important to dispose of the quitters and yolkers to limit the chances of bacteria from multiplying inside the eggs and exploding inside the incubator. Eggs that explode inside the incubator put the rest of the eggs at risk of becoming contaminated too.
Tip #10: Limit Candling to 10 Minutes
Candling is not going to hurt the developing embryos if you keep it to maximum of 10 minutes. Mother hen will leave her clutch of eggs each day for about 10 minutes, the amount of time it takes her to relieve herself and to eat and drink. Try to simulate this when you do your candling. The time that is.
Tip #11: Make it a Family Experience
Make it a family experience. This is an excellent learning opportunity for the whole family, not just adults. This can teach children about the life cycle of baby chicks and the importance of responsibility. Before you know it, the wait will be over and you will be able to enjoy your new baby chicks!
Simple Step by Step Instructions for Candling Chicken Eggs
Step 1: Wash your hands with warm, soapy water for 30 seconds.
Step 2: Place a clean towel down on a table where you will be doing your candling.
Step 3: With clean hands, wipe down your candling device/flashlight using a sanitizing wipe and place it on your clean towel.
Step 4: Have a pencil handy to mark the air cell and a piece of paper to jot down any notes that you want to take on the eggs you are candling.
Step 5: Bring the eggs into your candling room and carefully remove one egg at a time to candle.
Step 6: Shine a bright light over the top of large end of an egg. If you need to, cup your hand around the edges of the flashlight to seal the light in. Amazon sells some pretty good egg candlers. You can check out their varieties and prices below.
Step 7: If you cannot see any movement, very gently rock the egg back and forth. Sometimes this is enough to stimulate the embryo to move.
Step 7: With your pencil, draw the outline of the air cell. As days go on, it should gradually increase in size.
Step 8: Keep track on a piece of paper eggs that you question the viability of.
Step 9: Try to candle all of the eggs within a 10 minute time frame. The shorter the eggs are exposed to different temperatures, the better.
Step 10: Have your filtered water ready to refill the incubator reservoirs prior to placing the incubator tray of eggs back in.
CONCLUSION 11 Best Tips: How to Properly Candle Chicken Eggs
- Always wash your hands before candling chicken eggs.
- Sanitize flashlight/candler before candling chicken eggs.
- Don’t wash eggs prior to incubating or candling.
- Candle in proper room temperature.
- Prepare a dark room with supplies before bringing chicken eggs in to candle.
- Choose a time to candle when you are not rushed.
- Don’t candle too often. Only candle on designated days.
- Mark air cell of chicken egg with pencil.
- Dispose of “Quitter” and “Yolker” chicken eggs.
- Limit candling to 10 minutes.
- Make it a family experience.
