A comprehensive resource to learn all about the egg float test (egg freshness test) and the science behind it, how to tell if eggs have gone bad, when to toss them, and how to properly store eggs.
Eggs are truly an incredibly food.
Eggs are a complete protein (about 6 grams / 12% protein per egg) and they contain essential amino acids, loads of vitamins, and only 70 calories per egg.
In cooking and baking, eggs act as an emulsifier, thickener, add richness and flavor, structure, leavening, and more. So it’s kind of a big deal – a super ingredient, if you will.
In this cooking and baking 101 article, I discuss egg basics, how to tell if eggs are fresh, and the applications for your eggs at different stages of freshness.
What happens with an egg float test and what it means
The egg float test is a popular method to use to tell how fresh an egg is, and if it has become stale.
Some also think of it as a test to check if an egg has gone bad, but this isn’t accurate – because fresh eggs can also go bad.
The egg float test is done by carefully dropping an egg into a bowl filled with water. The egg will either sink to the bottom of float, or something in between. The way the eggs settles in the water is an indication of the freshness of the egg.
Stage 1 – Fresh Eggs
The egg sinks right to the bottom and lies horizontally at the bottom, because the egg is at its heaviest mass. The egg was laid within a few days, and is very fresh.
Has the thickest egg white, egg yolk, and the smallest air pocket. It’s hard to purchase eggs that are this fresh, unless you get them directly from a farm.
Uses
- Perfect for poached eggs – Since the egg white is thick and doesn’t spread, it works well for poached eggs.
- Good for meringues – You can make meringues (like Swiss meringue) with fresh eggs. The egg whites are the most stable. HOWEVER, the volume that you can get from fresh egg whites is a little less because fresh egg whites don’t whip up as much as older egg whites.
- Not good for hard boiled eggs – The egg shell won’t peel easily with fresh eggs. No matter what tricks you try, the shell is more prone to sticking to the egg when the egg is at its freshest.
Stage 2 – Eggs that are a few weeks old
At this stage, the eggs still sinks to the bottom, and is still touching the bottom of the glass. But one end of the egg starts to tip upward at an angle (up to 45 degrees). The egg is about 1 – 2 weeks old.
The egg white is still slightly thick, but is starting to become thinner.
Uses
- Perfect for meringues – Because the egg white still has some stability, and can also create a more voluminous foam.
- Good for hard boiled eggs – Eggs that are angled at about 45 degrees are between fresh and stale stages, so they are good for hard boiling as the shells should peel more easily.
- The more angled the egg, the less suitable for poaching – As the egg whites can spread too much in water.
Stage 3 – Eggs that are about 1 month old
At this stage, the eggs still sink to the bottom and are touching the bottom of the glass. However, the egg is pointing straight up rather than lying horizontally or at an angle.
The egg white is thinner and the yolk breaks easily.
Uses
These egg whites will produce the most volume, but will also be the least stable. You can still use these eggs for meringue buttercreams (like Swiss meringue buttercream), but I would not recommend them to make pavlova, or baked meringues as the foam can easily collapse.
The eggs will peel very easily when hard boiled.
Not suitable for poached eggs at all.
These eggs are almost stale, so must be used ASAP.
Stage 4 – Eggs that are over 2 months old
These eggs float in water. The egg does not sink to bottom, and is not touching the bottom of the glass. However, the egg can float just above the bottom of the glass, or float at the surface.
These eggs are stale. The egg whites are very thin, the yolks can break merely by opening the egg.
I do not recommend that these eggs be used for consumption.
While they may not have “gone bad”, they are stale, and have a higher risk of carrying Salmonella or other bacteria inside.
Why does the egg float test work? (the nifty science)
To understand why this happens, let’s first check out the components inside an egg.
Parts of an egg
There are many components to an egg, but let’s simplify them to,
- Egg shell
- Egg white
- Egg yolk
- Chalaza (the springy cord that holds the yolk in place)
- Air cell
- Egg membranes (egg shell membranes and egg yolk membranes)
Eggs are semipermeable. This means the egg shell membranes allow for the exchange of selective molecules such as air and water. This allows for exchange of air if a chick is growing inside a fertilized egg.
As soon as an egg is laid, it’s at its freshest. The longer the eggs are stored, the more air and moisture exchange between the eggs and the environment. This exchange of air, moisture, and other molecules creates changes within the egg.
A fresh egg that has just been laid has a strong, thick egg white. The egg yolk is also plump, and not easily broken because the membrane around the yolks is stronger too. When a fresh egg is cracked the egg white doesn’t spread as much and has greater height (when looking from the side) as well. A fresh egg ALSO has a neutral pH.
What happens inside the egg as the egg becomes stale
Most people think the egg floats in water because the air pocket becomes bigger. While the air pocket does become slightly larger, it’s not enough to make a stale egg float. The egg also loses its density to become lighter, with age.
There is an exchanging of air from the outside and the inside of the egg, including the air pocket. The egg white and the egg yolk also start to change and release gasses that escape through the egg shell.
As the gasses escape through the shell, the egg becomes more alkaline. The egg white and yolk texture changes – the egg white becomes thinner, and the egg yolk spreads and becomes weaker, making the egg less dense.
The moisture evaporates through the shell, and the air pocket becomes larger. The weight of the egg remains the same, but the density of the contents inside reduces.
This causes the egg to float as it becomes stale.
The exception to the rule
Egg grading is the only exception to the rule. Egg grading can be either AA, A or B.
This occurs when the eggs are fresh. Grade AA eggs will have smaller air pockets and tighter egg whites than grade B eggs. Grade AA and A eggs are usually found in the supermarket, and grade B eggs are usually used for other egg products.
Other ways to test for egg freshness
Of course you don’t have to do the float test to know when eggs are fresh or not so fresh. There are other easy ways to check it as well.
Check the expiration date on the carton
There should be a pack date or expiration date and it’s important to use the eggs within that time.
FUN FACT: Some countries do not store their eggs in the fridge, and they can be stored at room temperature. But in North America, we have to store our eggs in the fridge. So make sure to refrigerate the eggs if you need to, and use them by the use-by date. If you keep the eggs at room temperature, the use by date will likely be much earlier.
Visual inspection
As mentioned in the post, a fresh egg has a really thick and tightly compacted egg white, and a plum egg yolk. If the egg white spreads very wide and thin (like water), those eggs are usually stale!
The egg yolk will also spread flat, if you do not accidentally break it when cracking the egg – because the egg yolk membrane will break so easily.
Also, do not use eggs that have cracks on the shell either. These eggs can easily harbor bacteria and go stale and / or go bad even faster.
How to tell if eggs are off
Since the float test does not indicate that an egg has gone bad, how do you tell if an egg has expired or has become rotten?
The smell test
This is the most obvious and easiest to check if the egg has gone bad. If you open an egg, and it has a sulfur smell (i.e. rotten egg smell), or an off smell, it’s gone bad and need to be tossed. A good egg should not smell bad. A rotten egg will have a very strong sulfur smell that you cannot miss.
Changes in color
The egg white is clear, and the yolk should be yellow (or orange). There should not be any weird white patches or off colors in the egg white or yolks. The exception to this is having any blood spots on the egg yolk or whites. This is generally normal and has no effect on the egg. Some rotten eggs also have dark brown or black patches (from bacterial or fungal contamination).
Changes in texture
The egg white and yolk will look slimy, and might even stick to the shell when you crack open the egg. If there are any changes to the egg shell – like a powdery residue, or a slimy appearance, then it must be tossed out as well!
Proper egg storage
In North America, the out layer of an egg is washed off before selling the eggs to consumers. This layer is called the cuticle. In some parts of the world, the cuticle is not removed, and the egg is not refrigerated as it’s believed that this layer acts as an antibacterial layer.
But according to the FDA, the preferred method of extending the life of eggs is to wash the cuticle layer and to refrigerate the eggs. So it’s crucial to refrigerate eggs to extend their shelf-life. Refrigeration also slows down salmonella contamination.
To prevent fluctuations in temperature, the official recommendation is to store the eggs in the paper carton that you bought the eggs in, and to place them at the back of the fridge, where it’s coldest (without freezing).
The eggs will go stale significantly slower when stored in the fridge (temperatures that are lower than 40 F / 4 C).
Storing eggs in the freezer
Yes, you can store eggs in the freezer for up to 1 year! According to USDA guidelines, the egg shells should not be frozen, and instead the egg should be cracked into freezer-friendly containers prior to being frozen.
These eggs must be thawed out in the fridge and used immediately after. Frozen eggs also must be used in applications where the eggs will be fully cooked, so no raw egg applications. Also note, the yolk does change in texture once thawed, and it might be hard to emulsify it properly.
Ideally, I prefer to store whole eggs in the freezer AFTER blending them, so that it’s easier for me to cook them fully. Egg whites can also be stored in the freezer for up to 1 year.
If they were stored properly (with no fat contamination), they can be thawed out and used for making meringue as well! Just make sure they are at room temperature for about 30 minutes, because warmer egg whites are easier to whisk.
There is also a likelihood that these egg whites may not create the most stable meringue foam, so use it for applications where foam stability is not as important – like swiss meringue buttercream.
When to toss eggs
I do not recommend using eggs that are floating in the water (egg float test). While they may not be rotten or have gone bad, they are stale. Bacteria can enter through the shell and membranes more easily if the egg is older, and you certainly do NOT want to run the risk of salmonella contamination / food poisoning.
I also obviously do not recommend using eggs that have gone bad! You usually only know this when the egg shell is cracked. If the egg smells bad, has a slimy appearance, or has discoloration (that is not minor blood spots), then the egg must be tossed. The smell is the number one noticeable change.
White vs brown eggs, and other differences
There are many different types of egg in the market now. Caged vs free range vs organic, omega 3 eggs, white eggs vs brown eggs, and even other colored egg shells.
The lifespan of an egg is not affected by the color of the egg shell, or the diet of the hens that lay the eggs. So there is no significant nutritional difference between white or brown or blue egg shells.
Omega 3 eggs are from hens that are fed a diet higher in omega 3, while organic eggs are from hens that are fed an organic diet. There are also some eggs that have a deep orange colored yolk, when usually it’s a more yellow color. This color difference is due to the diet of the hens (higher carotenoid diet leads to a more orange yolk).
There is no change in the nutritional value, but there might be slight changes in the flavor of the eggs, and obviously the final color of the product that uses these eggs.
Informational videos on eggs
Frequently asked questions
Eggs can stay fresh in the fridge for a few weeks! This depends on when you buy the eggs. According to the FDA, eggs should be used up within 3 weeks. However, other sources say you can store eggs for about 4 – 5 weeks!
Since I do eat and use lots of eggs in my cooking and baking, the eggs don’t really last longer than 3 – 4 weeks at most.
An egg will lose its freshness in 1 – 2 days at room temperature, comparable to an egg stored for 7 – 10 days in the fridge.
Eggs stored at 40 F / 4 C, will last long in the fridge and in reality will not go bad that quickly because of the low temperature.
But in reality, we open the fridge regularly causing fluctuations in temperature. This can affect the longevity of the eggs.
The more we open the fridge door, it can shorten the lifespan of the egg. If your egg is within the expiry date or sell by date, then you’re safe. It’s not advisable to consume eggs past their expiry date.
But, if your eggs are still sinking right to the bottom (and touching the bottom of the bowl) with the egg float test, then you theoretically can eat the egg. However, please be cautious.
Not very long!
USDA guidelines treat eggs just like they would any other meat product and do not recommend storing it at room temperature for more than 2 hours.
In reality, I am guilty of storing my eggs at room temperature out of habit (from living in other countries in the past). And have been intentionally trying to remember to store them in the fridge ASAP.
I’ve found that these eggs go stale much faster at room temperature. After about 5 days, these eggs will be more susceptible to salmonella contamination.
It is! As far as egg freshness is considered. An egg float test will not tell you if an egg has gone bad. The most accurate test for this is the sniff test to make sure your egg doesn’t have a sulfur smell.
The egg float test is also great for when you’re not sure if you have eggs fresh enough for poaching. Or if your eggs have aged just enough to be used for hard boiling, so that they are easier to peel!
Plus, I do use the float test to make sure my eggs are not too stale for making pavlova, or other meringues like swiss meringue for topping desserts.
