Brooke Martin
Candling is a technique used to examine the contents of an egg without breaking it open. It involves placing a bright light source, such as a candle or a modern LED torch, behind an egg to illuminate its interior. This method allows people to check if an egg is fertile, monitor the growth and development of an embryo, and assess the quality of edible eggs. Candling is also used in lutherie to check the thickness of instrument soundboards and identify any flaws in the wood. To sell eggs in certain places, such as Georgia, farmers are required by law to candle their eggs.
| Characteristics | Values |
|---|---|
| Purpose | To check if an egg is fertile and developing properly |
| How it works | Uses a bright light source behind the egg to show details through the shell |
| Embryo development | By Day 6-7, a fertile egg will show a dark shape and spider-like veins; by Day 14, the egg will be mostly dark with less visible light passing through |
| Early embryonic death | A thin ring around the inside of the egg indicates early death, which can occur at the beginning of incubation or within the first week |
| Humidity | Correct humidity is crucial during incubation; can be monitored by checking the size of the air sac using a diagram or a high-tech solution like a wireless sensor |
| Building your own egg candler | Place a desk lamp with a bright low-energy lightbulb inside a cardboard box with a small round hole at the top for the pointed end of the egg |
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What You'll Learn
Embryo development
On day 3, veins may start to become visible, radiating from the centre of the egg outwards. By day 6 or 7, a dark shape, the embryo, and spider-like veins should be visible. If the egg is infertile, it will appear clear with no dark spot or blood vessels.
On day 8, the embryo will be more developed, allowing one to see the chick wiggling and kicking in the egg. The air pocket in the egg should be getting larger, and the egg will be getting darker as it fills with more bird.
By day 14, fertile eggs will be mostly dark, with less light passing through. If there is no change by day 14, it could indicate that the chick stopped developing.
During the last 3 days of a hatch, it is best to avoid candling unless necessary, as the embryos will have developed significantly, filling the inside of the egg, and little can be seen.
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Egg quality
Egg candling is a method used to assess the quality of eggs meant for human consumption. It involves checking the amount of air inside the shell, the egg's air cell, the yolk, and the albumen or egg white. These factors are used to determine whether an egg should be graded AA, A, B, or deemed inedible. Candling is also used to check if an egg is fertile and developing properly.
To candle an egg, one must use a bright light source behind the egg to show details through the shell. The process gets its name from the fact that candles were the original light sources used. Today, one can use a desk lamp with a bright, low-energy light bulb, a modern LED torch, or an egg candler, which can be either mains-powered or battery-operated.
When candling an egg, it is important to maintain the correct temperature and humidity to avoid damaging the embryo. The egg should be returned to the incubator as quickly as possible to preserve heat and humidity levels. One way to confirm the humidity of the incubator is to monitor the air-sac size. If the air sack is too small, the incubation humidity is too high, and if it is too big, the humidity is too low.
There are two high-risk periods for embryo death: the beginning of incubation and just before the chicks hatch. A thin ring around the inside of the egg indicates early embryonic death, which occurs when the embryo dies at the start of incubation, usually within a couple of hours. This type of egg is easy to identify and remove.
Candling is a useful method for those who raise backyard chickens and want to ensure a steady supply of fresh eggs. In Georgia, for example, it is required by law that eggs be candled before they are sold.
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Humidity and temperature
Candling an egg involves inspecting it before a penetrating light in a darkened room to check for signs of fertility, defects, or freshness. It is a good idea to candle eggs on days 7 and 14 of their 21-day incubation period. This is because eggs are temperature-sensitive, and constantly moving them in and out of the incubator could negatively affect their development. Additionally, before day 7, the eggs will not have developed very much, and it will be challenging to distinguish between good and bad eggs.
The humidity and temperature of the incubator are critical factors in the successful incubation of an egg. The humidity level should be adjusted according to the size of the air sack in the egg. If the air sack is too small, the incubation humidity is too high, and if it is too big, the humidity is too low. Humidity is challenging to get right during the incubation period, and even incubators with automatic humidity control can fluctuate or run dry.
To compensate for humidity fluctuations, some people use wireless sensors, such as the SwitchBot sensor, which can be connected to a phone via Bluetooth or the internet. These sensors allow users to view temperature and humidity graphs and make adjustments as needed.
Maintaining the correct humidity and temperature is crucial to prevent embryo deaths during incubation. Incorrect humidity levels can cause egg weight loss during incubation, and temperature fluctuations can cause embryo deaths, especially if the temperature is too high.
It is also important to note that eggs should not be moved or turned in the days leading up to hatching, and the humidity level should be raised to around 70% on day 18.
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Early embryonic death
Candling an egg involves shining a bright light into the egg, allowing the observer to see its contents and check whether it is developing properly. This is done to identify infertile eggs that do not contain developing embryos, which can be removed from the incubation process. It is also used to detect early mortality, preventing the potential for contamination from decomposing embryos.
The most common causes of early embryonic death are rough handling, incorrect storage (such as storing for too long or at the wrong temperature), adverse genetic traits, or ageing of the breeder flock. Candling an egg can help identify early embryonic death by revealing a small dark area and disrupted blood vessels. Deteriorating blood vessels will often appear as a dark or blood ring around the egg.
It is important to note that candling may not always provide a definitive answer, and other factors such as the size and colour of the egg can affect the accuracy of the process. Additionally, the timing of candling can impact its accuracy, with days 9 or 10 being recommended to minimise errors.
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Egg candling history
The term 'egg candling' originates from a time before electric light bulbs, when people used candles for light. The technique involves placing a candle inside a wooden box with a small hole at the top, allowing light to pass through an egg placed on top of the box. Candling was first used to check on the development of embryos in incubated eggs, and it is still used for this purpose today, especially by those who hatch their own chicks.
The method was first used by poultry breeders, who would inspect the eggs by candlelight and discard any that were bloodshot. In the 1920s, Izzy Horowitz worked as an egg candler in Brooklyn, and by the 1930s, electric egg candlers were in use.
Candling is a useful way to check the quality and development stage of an egg, and it can also be used to assess the quality of certain translucent plant seeds, especially those of lilies and their close relatives. It is a simple method that can be performed at home, with a bright light shone through the egg in a darkened room. The light shows details of the egg's interior through the shell, and candlers can look for signs of fertility, defects, or freshness.
The size of the air cell at the wide end of the egg indicates its freshness, as it shrinks with age. The shadow cast on the shell by the yolk also indicates the egg's age, as older eggs have thinner albumin, and the yolk sits closer to the shell, casting a sharper shadow. Candlers can also detect the size, shape, and colour of the yolk, as well as the presence of blood clots.
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Frequently asked questions
Egg candling is a method used to check if an egg is fertile and developing properly. It involves placing a bright light source behind the egg to show details through the shell without breaking it open.
Candling an egg can show if an egg is fertile or not. A non-fertile egg will look clear with no dark spot or blood vessels. A fertile egg will have a dark shape and spider-like veins.
The term "egg candling" comes from the past when people used candles as a light source to illuminate eggs and determine their contents.
Candling uses a bright light source, such as a modern LED torch or a desk lamp placed inside a cardboard box, to shine light through the egg and reveal details about its contents.
Candling eggs can help farmers determine the quality of the eggs for human consumption and check on the development of the embryo inside without damaging it. It can also be used to assess the humidity of the incubator and prevent contamination in the hatchery.
