How to Candle Eggs During Incubation?

Egg candling is an important way of checking on the progress of the incubation process.  It allows for removal of non-viable eggs during the incubation process which is important.  Failure to remove dead eggs can lead to contamination to the embryos that are developing properly. This page details how to candle eggs.

An egg candler is the tool used to do this.  An egg candler focuses a beam of light to allow the egg to be held or placed upon it.  This allows the user to see what is going on inside the egg.  The process is usually carried out in a darkened room.

Before starting to candles it is important to note that eggs should stay out of the incubator for maximum of 2 minutes. With a little experience, and if you use the egg tester, you can candle the eggs without lifting them. In this case, open the incubator and lay the egg tester on each egg. The beam allows you to see the embryo.

Never shake or turn violently hatching eggs as this can break the blood vessels and therefore cause the death of the embryo.

The timing of the checks is as follows.

Timing of Egg Candling during Incubation

1st check

The first check is to verify that incubation has begun.


Normally it is difficult to see the embryo, as it is incorporated in the yolk: next to the air cell and at its point you shall see blood vessels.


If the egg is not fertilized its inside is uniform, doesn’t show blood vessels and the yolk is right in the middle. Discard these eggs. It is possible that eggs with a thick shell or brown ones don’t allow a clear view of their interior at this stage: leave them to the second check or used a higher powered egg candler.

2nd check

With this check you are checking on the development of the embryo.


You will normally see a network of blood vessels at the point of the egg and the embryo will look like a dark spot.


If the blood vessels are not present, it means that the embryo is lost.  The egg should be discarded.

3rd check:

In this check you are verification the embryo is alive prior to the before moving to hatching stage of incubation, during the last three days.


Normally the embryo occupies the entire egg.  Blood vessels should not be visible at this stage. The air cell should be big.


If the embryo doesn’t fill the whole egg and blood vessels are still visible, then the air cell is small and the albumen has not been used up.  This means that the embryo is underdeveloped and the egg should be discarded.