Candling is the use of a bright light to shine through an egg to check fertility and embryology development.
Why Candle Eggs?
- If you leave eggs in your incubator that are not fertilized ("yolkers") or have embryos that have quit growing ("quitters"), your incubator (and room) will get very smelly. These eggs rot if left in an incubator!
- You can check to see how the embryos are developing.
How to Candle an Egg
You will need:
- A bright light. When our 4-H staff visit classrooms for candling, we use flashlights with bright LED bulbs.
- A dark room. The room should be near the incubator or in the same room as the incubator so you can put the eggs right back in after you are done.
If you are nervous about handling one of your eggs, practice first with an egg you bought from a grocery store. These eggs are not fertile.
When you are ready, turn on your bright light and shut off the lights in the room so it is dark. Without looking directly at the bright light, hold the larger end of the egg (which has the air sac) up to the light and slowly rotate the egg to see various structures within. The light won't hurt the embryo, but it isn't a good idea to hold the light up to the egg a long time, especially if the light gets hot.
Be very careful when you are holding the egg so you don't accidentally crack it.
When you are finished, carefully place the egg back in the incubator. After handling eggs, the incubator or chicks, wash your hands carefully.
What You May See
Do you see the air sac? Can you see the pores in the egg shell? Can you see the yolk? Do you see blood vessels or a thin red ring around the yolk? If the egg has been in the incubator for a week, you may see the embryo move! If your egg is colored or a brown egg, it is harder to see through the shell, you may want to wait a few days and try again.
Winners — When embryos have developed, we call them "winners." In the first few days, you may see a network of blood vessels. About day 7, you should be able to see the shadow of the embryo's body, its eye (which looks like a small black circle) and perhaps movement! The closer the embryo gets to day 21, the more blood vessels and structures you may recognize (such as the beak and feet).
Quitters — When embryos stop growing, we call them "quitters." You will see a thin, blood ring around the yolk. Quitters are removed from the incubator and thrown away. If you want to view the embryo, have your parent or teacher help you open the egg. Be sure to wash your hands afterwards.
Yolkers — Some eggs in the incubator may not be fertile. We call those "yolkers." When you look at a yolker, you won't see a spot in the yolk, blood vessels or a blood ring around the yolk. When we candle eggs in the classrooms and find a "yolker," students usually ask "Can you eat a yolker?" The answer is no — don't eat any eggs that have been in an incubator! Throw yolkers away.