You can tell whether the farm egg you just cracked open for your breakfast is fertilized or not. Examine the egg for the germinal disc, a white spot floating above the surface of the yolk. The germinal disk of a sterile egg contains only the hen's cells and is fully white in color.
Find out by candling
If the egg is fertile, then you should see a dark spot around the middle of the egg, with some spider-like veins beginning to form around it. If its not, you should just be able to see the shape of the yellow yolk inside the egg, without any signs of an embryo or veins.
“There is no embryo until heat is applied either through the hen sitting on the egg or by putting it in an incubator.” She says a fertilised egg doesn't taste any different and won't harm you. Indeed, in the days when most eggs came from farms that kept cockerels, almost all eggs would have been fertilised.
Does the big end stick up above the water with the narrow end pointing straight down? Your egg is probably a “yolker” that either was a dud from the beginning or died young. On the other hand, if your egg floats at more of an angle, almost horizontally, the chick might be alive inside.
That means the chick inside the egg has broken through the internal membrane in the egg. This can be seen by candling the egg (shining a bright light through the egg). Most of the egg will be dark, but at the blunt end where the air sac is, one is able to see the chicks beak in the air sac (and often hear them peeping.
The best kept secret in determining an egg's freshness is to see if it sinks in water. To try the egg water test, simply fill a glass or bowl with cold water and submerge the eggs. If the eggs sink to the bottom and lay flat on their side, they're still fresh.
The water test for egg freshness
First, fill a bowl or glass with about four inches of cold water and gently place your egg(s) inside. Very fresh eggs will sink to the bottom and lay on their sides. If an egg stays at the bottom but stands on its small end, it's still acceptable to eat; just not quite as fresh.
If the air pocket becomes large enough, the egg may float. While this method may tell you whether an egg is fresh or old, it doesn't tell you whether an egg is good or bad (2). An egg can sink and still be bad, while an egg that floats may still be fine to eat (2).
Healthy female chickens, known as hens, are able to lay eggs, whether or not a rooster is present. Eggs will be unfertilized if the hen has no access to a rooster, which means the egg will never develop and hatch into a chick.
You can tell whether the farm egg you just cracked open for your breakfast is fertilized or not. Examine the egg for the germinal disc, a white spot floating above the surface of the yolk. The germinal disk of a sterile egg contains only the hen's cells and is fully white in color.
You'll only need to open 1 or 2 in the few days running up to your incubation. When you crack open the egg, if it's fertile, you'll notice a small white spot on the top of the yolk about 4mm in width. This is called the germinal disc. This is what tells you if the egg has been fertilised.
If you are not sure whether the embryo is alive, place the egg back in the incubator and retest later. A second test can be made after 14 to 16 days of incubation. If the embryo is living, only one or two small light spaces filled with blood vessels can be seen, and the chick may be observed moving.
Chances are you've never eaten a fertilized egg, because nearly all eggs sold commercially are produced by hens that have not mated, says Lauren Cobey, media representative for the American Egg Board. The difference between fertilized and unfertilized eggs comes down to whether a rooster has been involved or not.
The oldest and easiest way to tell if an egg is fertilized is called candling the egg. It is literally holding the egg up to a lit candle {not to warm it, but in order to see inside of the egg}. You can also use a very bright small flashlight. If the egg appears opaque, it is probably a fertilized egg.
Did you know you can determine if an egg is fertile or not by looking at the germ spot? The germ spot is the white spot on the yolk. The non-fertile germ spot contains only the female's cells and looks like a solid white spot. In a fertile egg the germ spot contains both the female and male cells.
If refrigerated, eggs typically stay safe well after their expiration date. Regardless of what that date actually is, the optimal storage time for raw eggs in their shells, according to the USDA, is three to five weeks.
If it sinks to the bottom, it's fresh, perfect for poaching and soft-boiling and making souffles. If it stays submerged with its wide end up, it's older but still good for most uses, especially hard-boiling (where the egg is cooked all the way through). If it floats, toss it. That's a bad egg.
The older a raw egg gets, the more air becomes trapped in an air chamber located at the wide end of the egg. As others have pointed out, when you cook an egg in boiling water, the air will expand too quickly and will burst the shell — the same way a balloon will pop with too much air.
Broiler eggs exposed to LED light showed an increase in hatchability (90.12%, P=0.03) and an increase in no-defect chick percentage (86.12%, P=0.04) at hatch compared to the DARK chicks (85.76% and 69.43%, respectively). Differences were observed between treatments during the 14 d grow-out.
In candling, you'll be able to see your developing chick moving. Soon after that, you'll be able to see very little. As the chick grows and starts to fill more of the egg, candling becomes more difficult - the chick's body simply gets in the way.
The most accurate way of testing whether your eggs have gone bad is to crack them open. If the yolk or white has any discoloration, the egg is no good. Discoloration is an indication of bacterial growth. If your eggs look good but have an off or sulfuric smell to them, they are bad.
The main risk of eating bad eggs is Salmonella infection, which can cause diarrhea, vomiting, and fever. A person can reduce the risk of Salmonella by keeping eggs refrigerated, discarding any with cracked shells, and cooking them thoroughly before eating them.
Whether you raise, sell, give away or purchase farm fresh shell eggs, you can enjoy safe fresh local eggs when they are properly cleaned, candled, graded, sized, packed and stored.