A rotten egg in an incubator looks dark and cloudy when candled, often showing a black mass or a distinctive red/dark ring (the "red ring of death") where the embryo died, and it usually emits a powerful, foul odor, sometimes leaking brown liquid or having a slimy, discolored interior, indicating bacterial growth and potential for explosion.
If a ring of red is visible within the egg, there was an embryo at some point, but it has died. Remove this egg from the incubator. If you can see blood vessels within the egg, there is a live embryo inside. Blood vessels in chicken eggs are normally observable within 7 to 10 days of an egg's incubation.
🥚🐣🔦 As you'll see, an egg with NO chick embryo inside (like egg 1) will almost seem transparent and empty. It will glow orange from the light but won't have any dark spots inside.
Sniff Test
If you don't have the best before date, it's sometimes possible to determine a bad egg simply by smelling it. Good eggs don't smell at all but off eggs will emit a slight sulfuric smell that warns you something isn't right. If you're unsure, crack the egg onto a clean plate to smell it properly.
A blood ring or the ring of death is when an embryo fails early into incubation. This egg began to develop and somewhere along the way the embryo passed away. Once it passes the blood moves away from the embryo forming the ring you see here.
A nice, ripe egg will explode with balloon-like force and sound. When candling eggs, pay attention to any smell inside the bator to catch rotten eggs early. Bad eggs readily identify themselves and should be removed immediately.
A loud bang, followed by a very bad smell, are the usual signs. This phenomenon is caused by gas-producing bacteria, often Pseudomonas spp., inside the egg. Pressure inside such an egg builds up and even a small vibration can be enough to trigger the explosion.
Typically, if an egg has not hatched by day 24, it's almost certain that it will not hatch. By this time, all viable eggs should have hatched. Before disposing of unhatched eggs, it's prudent to candle them one last time to confirm there's no chick inside.
During candling eggs with a developed embryo will appear dark. A clear egg may be infertile or contain an early dead embryo. clears needs to be completed. Dark eggs contain a live embryo.
Give it 24 hours to progress from pip to hatch. If no progress has been made after 24 hours, Intervene by slowly chipping tiny pieces of the shell. If it starts to bleed, stop and wait a bit before proceeding again. If progress is being made after 24 hours, continue to wait.
Possible signs and symptoms of salmonella infection include:
Older Eggs: Sink but stand upright. Bad Eggs: Float to the top — discard them! Why Do Old Eggs Float? As eggs age, moisture evaporates and air enters the shell, causing the egg's internal air cell to grow.