How to make a Naked Egg
A “naked egg” is an egg that has no shell. Let me say that again, an egg with no shell. This is not something you normally run across and even when I show a naked egg to someone they often just don’t get the idea that the shell is gone – yet the egg stays intact. You might want to check out the anatomy of an egg to get an idea what we are dealing with.
The shell of an egg (typically a chicken egg) is made up of primarily calcium carbonate. If you soak this egg shell in vinegar (which is about 4% acetic acid), you start a chemical reaction that dissolves the calcium carbonate shell. The acetic acid reacts with the calcium carbonate in the egg shell and releases carbon dioxide gas that you see as bubbles on the shell.
CaCO3 (s) + 2 HC2H3O2 (aq) → Ca(C2H3O2)2 (aq) + H2O (l) + CO2 (g)
The egg insides remain intact and are held together by the two fragile membranes just inside the shell.
Here’s what you need
Let’s get to the fun stuff. In order to make a Naked Egg you will need the following items:
- Vinegar (at least 16 ounces)
- A couple of glasses or cups
- Raw eggs
The process is really very simple. Carefully place the egg in a cup and fill the cup with vinegar so that the egg is completely covered. Don’t worry if the egg floats a bit. Just get enough vinegar in the cup to mostly cover the egg.
An egg soaking in vinegar with part of it’s shell dissolved.
Now the hard part – you will have to wait as the acetic acid in the vinegar begins to react with the calcium in the egg shell. In just a short while, you should see some bubbles appearing on the outside of the egg. These are bubbles of carbon dioxide gas from the reaction. It can take 12-24 hours before a good portion of the shell is removed. A good sign of progress is a white frothy scummy layer on the top of the surface of the vinegar.
After a day of soaking you can carefully remove the egg from the vinegar. I would suggest pouring the liquid into another cup and catching the egg in your hand. Using a spoon to fish the egg out might seem like a good idea, but I’ve seen a few eggs break or get damaged when using a spoon to remove them.
At this point you may be able to literally rub the shell off the egg with your fingers. It will rub off as a white powdery substance. Give it try, just be very careful, you don’t want to break the egg, it’s getting more fragile as the shell is slowly dissolved. Depending on your particular egg, you may already have a naked egg. However, I would suggest you fill a cup with fresh vinegar and soak the egg for at least one more day.
After two days of soaking you should have a pretty cool Naked Egg. Notice that the egg is a bit bigger than when you first started. This is because some of the vinegar (and some of the water in the vinegar) has moved through the membranes to the inside of the egg. The membranes are semi-permeable and allow water to move through them. This is called osmosis.
Fun things to do with your naked eggs
Naked eggs are cool, but experimenting with them is even cooler. You have probably already noticed that your naked egg is kind of rubbery. How far above the table can you drop your egg and have it survive by bouncing? I would suggest you start at one inch, then try two inches, and so on. Keep in mind that eventually this is going to get messy when it the membrane breaks. You might want to do this experiment outside.
If you want to see your egg get really big, simply put it in a cup filled with water. The makeup of the inside of the egg is around 90% water. If you put the egg in a cup of (100%) water, the water will begin to move inside the egg through the membrane to equalize the amount of water inside and outside of the egg membrane. This process of water moving through a membrane is called osmosis. Osmosis equalizes – or makes the concentration of water on both sides of the egg membrane the same. This means the egg will swell as the water moves inside and get larger.
You can even color the inside of your egg if you soak it in some water with food coloring. This is a nice way to verify that the water in the cup is really moving through the egg membrane and not just coloring the outside.
A naked egg that was soaked in corn syrup for a few days. Much of the water inside the egg has moved out through the membrane.
Shrink your Egg
Now that you know about osmosis, you might ask “can I make my egg shrink” or shrivel up? Of course, you just need a liquid that has only a little bit of water. A common substance you may have at home that fits this requirement is corn syrup.
Slip your Naked Egg into a cup filled with corn syrup and let it sit for a day, or two, or more and you will begin to see your egg begin to shrink and look sort of baggy. Corn syrup has very little water content. Once inside the syrup, the water inside the egg begins to move across the semi-permeable egg membrane to equalize the water concentration. Again, that’s osmosis at work. If you leave your egg in the syrup long enough it will begin to look something like a huge raisin – with of course a yoke inside.
If you get tired of the shriveled egg look, you can reverse the process by just dunking the egg back in a cup of water. The water will once again move across the membrane and fill the egg with water again.
A big thank you to one of our visitors who grabbed a great photo of what happens when you soak a naked egg in corn syrup for a few days. I might call it a “dehydrated naked egg.” And side-by-side is a brilliant red naked egg soaked in red food coloring. Thank you Evers Ding for permission to use your photo and check out the rest of Evers egg photos on his blog.
Can I eat the Naked Egg?
Several visitors have posed the question, “Can I eat my naked egg?” I would NOT recommend eating a naked egg prepared this way. Keep in mind you created your egg by soaking a raw egg in vinegar sitting at room temperature for a few days. That is not how to treat eggs you are going to eat! Even if you stored the egg in the refrigerator, I still would not recommend eating the raw egg. Some have asked if you could store the egg in the fridge, then cook it and eat it. Well, I suppose you could, but given the amount of vinegar that probably moved past the membrane into the egg, it’s most likely not going to taste all that great. Instead of eating your naked egg, just experiment with it.
A dehydrated naked egg side-by-side with a brilliant red naked egg soaked in red food coloring.
Look, if you are really interested in creating a Pickled Egg that you can eat, check out some of the recipes from the National Center for Home Food Preservation and for more information about safe egg handling practices check out the Egg Safety Center.
Does it Smell?
A few of you asked if the eggs will start to have that rotten egg odor after a while. Well, I think it depends on how you store the egg. That rotten egg odor comes from hydrogen sulfide. Eggs contains sulfur because it is needed for the production of feathers in the chicken.
I have not noticed any bad odors with my naked eggs. After dissolving the shell in the vinegar, I keep the egg in a glass of water for up to a week and have not noticed any odor when the egg does accidentally break. It would be an interesting (and probably stinky) experiment to leave an egg out for a week or two in order to give it a chance to start to decompose. I would suspect that as the contents start to decompose, sulfide compounds will begin to form and it will start to smell really bad.
Science Fair Project Ideas
In terms of doing a science fair project here are a couple variables you might want to explore in more detail. Just a list of ideas to get you thinking. If you come up with other ideas let me know!
- Change in the weight of the egg. The egg will swell as water is passes through the membrane after the shell is removed. If you have a scale that measures to something like a tenth or hundredth of a gram, you may be able to measure the weight of the egg from start to finish and estimate how much water is absorbed. Perhaps your school has a scale that could be used for this? You could also soak the egg in corn syrup and chart the lost of water as it moves out of the egg. Could be messy as you would want to carefully wash off the syrup to make your weight measurements.
- Does temperature make a difference in how long it takes to remove all the shell? Eggs in vinegar in the fridge versus at room temperature vs simmering an egg in warm vinegar on the stove. Could be smelly.
- The effects of the concentration of the acetic acid. Typical vinegar is about 4-5% acetic acid. Many asian food markets carry Concentrated Vinegar
(~25% acetic acid). If you cant find the concentrated vinegar you could dilute the normal variety to various concentrations with water and see how that affects the time to remove all the shell. Do multiple eggs in order to collect more data points.
- Strength of the egg membrane. First make a dozen naked eggs so you can do multiple trials. Then test how much weight it will take to burst the membrane. This could be done by pressing ever increasing weight on the egg, or by dropping the eggs from successively higher heights until the membrane fails. This will probably be messy!
References
I’ve received many requests from students doing science fair projects related to the Naked Egg looking for further or deeper references. I have included some print references below. You can use the World Library Catalog to locate one of these items in a library near you!
- B. Z. Shakhashiri, Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol 3, p. 283-285, Wisconsin (1989).
- B. Cocanour and A. S. Bruce, J. College Sci. Teach. 15:127 (1985)
- V. L. Mullin, Chemistry Experiments for Children, Sterling Publishers: New York (1961).
- L. A. Ford, Chemical Magic, T. S. Denison and Co.: Minneapolis, Minnesota (1959).
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Totally cool! My grandkids and I are going to have a blast with this!
Hi,
can you eat a naked egg?? maybe hard-boiled?
thanks!
One of my students is doing something like this for her science fair topic this year-it was nice to come across your website and see what will happen. Go Green!
I would NOT recommend eating a naked egg prepared this way. Keep in mind you started this experiment with a raw egg and then let it sit at room temperature for a few days. That is not how to treat eggs you are going to eat.
If you are really interested in creating a Pickled Egg that you can eat, check out these recipes from the National Center for Home Food Preservation and for more information about safe egg handling practices check out the Egg Safety Center.
Love this!
We used to soak a hard boiled egg in something when I was a kid and it softened the shell enough that we could suck it into a bottle or shape it in a box. I thought it was vinegar that we soaked it in but I don’t remember exactly. Could that work or what should I soak it in?
Carri,
In order to “suck” and egg into a bottle you just need a peeled hard boiled egg. I suppose you could remove the shell with vinegar, but it’s probably quicker to just peel it. If you can’t find one of those old classic milk jugs you remember, something like a Sobe drink bottle will work. Check out this video that hits on exactly the experiment you are talking about. The first part is about the naked eggs, but about halfway into it I pull an egg into a milk jug.
The idea of making a square egg is intriguing! I’ve never seen that done, but if you succeed in doing so by soaking in vinegar, send me a photo!
I would be so awesome if it were possible to watch a baby chick grow in a Naked Egg?!?
Laura,
I agree it would be awesome to see the development of the chick. However, without the protective shell of the egg I doubt the chick would be able to survive.
The Exploratorium in San Francisco does have an exhibit that is very close to what you are talking about. It is a fascinating exhibit, but also a difficult exhibit for many people to come to terms with. Fertilized chicken eggs are placed in petri dishes where visitors can then observe the development of the chick over about a week of time. Since the chicks can not fully develop in the dish, after a time period they are disposed of.
I remember making hard boiled eggs square when I was a little girl. My mom had a little plastic “press” that would make it square after a few days.
To make square shaped eggs you just put them in a mold for about 10 minutes after they are boiled and are peeled.
That is amazing! I look forward to trying this out with my students and reading more of your fun activities!
Wow! Found this on pinterest and can’t wait to try it. Great ideas here.
I want to do this with fertilized eggs that when candled at 2 weeks had stopped growing, “quitters” . I have 2 incubators that I use at school to hatch chickens. What a neat addition to the incubator lessons.
We are in the process of this experiment right now for my sons Science Fair! Just started soaking the eggs today so I am excited to see what the next few days will bring. We have a few soaking in vinegar just in case…. We also want to try one with the food coloring! I’m assuming you add the food color after the shell comes off, is this correct?
I’ve heard of this experiment before, but the only reason I’ve never done it is because I was told that, when the egg does break, it stinks mightily… something akin to a very bad sulfur smell. Is this true?
what if you kept this experiment in the fridge?…could you then boil & eat it?…since the raw egg won’t be left out of the cold
Well, I think it depends on how you store the egg. That rotten egg odor you refer to comes from hydrogen sulfide. Eggs contains sulfur because it is needed for the production of feathers in the chicken.
I have not noticed any bad odors with my naked eggs. After dissolving the shell in the vinegar, I keep the egg in a glass of water for up to a week and have not noticed any odor when the egg does accidentally break. It would be an interesting (and probably stinky) experiment to leave an egg out for a week or two in order to give it a chance to start to decompose. I would suspect that as the contents start to decompose, sulfide compounds will begin to form and it will start to smell really bad.
Yes add the food coloring after the shell has dissolved. Don’t be shy with the amount of food coloring. If you use a lot you will get a very deep color inside the egg.
Even if the egg was stored in the fridge I still would NOT recommend eating a naked egg. I’m not sure how much of the vinegar may move through the membrane and into the egg, so it would probably not taste very good.
If you are really interested in creating a Pickled Egg that you can eat, check out these recipes from the National Center for Home Food Preservation and for more information about safe egg handling practices check out the Egg Safety Center.
Can you use apple vinegar?
Yes, any kind of vinegar will work.
seems like a fun way to do green eggs for my little sam i am.
Carl,
I was SO happy to find your site. I am a homeschooling mom and wanted to find that spark to put in our science lessons. Thanks so much for your enthusiasm, and imparting knowledge in really understandable terms! I will be using your site a LOT!
Can I subscribe to your blog for email updates. Naked egg thing was cool.
Just made these with my son and his friends. We are at the vinegar stage and they just giggled about the naked eggs!! Eggs being naked is funny apparently to 9 and 10 year olds. Haha… I guess when the shell is gone it will be cool!
“I would NOT recommend eating a naked egg prepared this way. Keep in mind you started this experiment with a raw egg and then let it sit at room temperature for a few days. That is not how to treat eggs you are going to eat”
Sorry?
Is this not how eggs are purchased from the supermarket?
Well, no, every supermarket I’ve ever purchased eggs from has had them stored in a refrigerated case of some sort, not sitting at room temperature and soaking in vinegar…
I did this experiment with my girls (5 & 7) and it was great fun. Though it turns out I had an allergic reaction to the vinegar/egg mixtures. It started with itchy palms and ended with full body hives. Totally survivable with a week of benadryl and steroids. Totally avoidable with a pair of medical gloves. Wear gloves.
Another fun thing to do is bounce the egg. I have the kids start very close to the table and drop it. The egg will bounce. Then we go a little higher each time until it breaks, When I originally found the experiment it was called “bouncing egg”. Thanks for more fun ideas to try with our bouncing egg.
Hi Emily,
Sorry to hear about your allergic reaction, that’s the first time I’ve heard of a whole body reaction to eggs and vinegar! If anyone else is sensitive to such I would also recommend wearing gloves when doing this experiment.
Hey there!
So cool that you did it with brown eggs so you could see the brown shell dissolve in the vinegar and reveal the inner egg!
Thank you for giving us something really fun and cool to do in science for our homeschool! Keep them coming – you’re going to be my kids’ new hero and inspiring them to question and explore is always good!
Do you know what would happen if I soaked the egg in vinegar that already had food coloring? Would the inside be colored too?
I know that if I dye it with food coloring after it is soaked, it will be colored inside, but
I was wondering if it was the same case for this.
My other question: Does the yolk stay liquid after you soak it?
Thanks!
If you soaked a boiled egg in vinegar, how fast would the shell dissolve and would it still be edible?
Doesn’t sound very appetizing…
What chemical in the vinegar causes the egg shell to dissolve?
What other liquids can I use in this experiment that dissolve the egg shell?
Mimi,
You have lots of good questions that could (I really mean should) be turned into experiments! The chemical in the vinegar that dissolves the shell is called acetic acid. You might want to try some other liquids you find in your kitchen to see if they have any effect on the shell. Let me know what happens if you add food coloring to the vinegar or what happens to the hard boiled egg in vinegar!
What’s the best way to store a naked egg for a couple of days?
Just place the naked egg in a glass of water, it will swell a bit, but will be fine for quite sometime.
Thanks!
This is a common Biology lab for middle school students. The purpose is usually to demonstrate diffusion and tonicity effects on animal cells. (The unfertilized egg is just one cell!) IT IS BEST TO USE OLD EGGS. Older eggs go through pH changes that will make the membrane less likely to pop. I found it interesting that you mention storing the egg in water – in lab, about 1 out of every 5 eggs break during the water bath phase of the lab. To answer one commenter, YES, YOU CAN ADD COLORING TO THE VINEGAR and it will work fine. However, you may wish to view the yolk through the transparent membrane (undyed) before coloring the egg. Generally the lab is avoided by teachers due to the vinegar smell, not a gross egg smell. To avoid this, COVER THE VINEGAR with plastic wrap or a sandwich baggie while you soak the egg to avoid a vinegar-scented house. When dumping the vinegar, rinse it down the drain with water. For faster/easier shell removal, dump and refresh the vinegar (as suggested). To be ‘cheap’ – just soak the egg in the same vinegar for longer (as us teachers do). One commenter asked about “vinegar substitutions” and how it works. You need that acid. Chances are, vinegar is the best you will have in your kitchen. Some teachers use stronger acids to speed up the process, but vinegar is safer for household use.
Here is the chemistry lesson portion (sorry the subscripts don’t work):
Vinegar contains acetic acid (CH3COOH) in water. Egg shells are mostly made up of hard calcium carbonate (CaCO3). Acetic acid (a liquid) breaks apart calcium carbonate (a solid) into two pieces: calcium (Ca) & carbonate (CO3). The calcium pieces go into the vinegar solution. The carbonate pieces go through chemical changes with the acid to form water (H20) and carbon dioxide (CO2).
CaCO3 + 2 CH3COOH > Ca(CH3COO)2 + H20 + CO2
Kids love this lab, they become very attached to their little egg babies if you allow them to name them. I have a Day by Day lab worksheet if homeschooling parents want one.
We get these at work, wothout all the fuss! Still a fun eggsperement/
i actually made one and now im cooking it , it looks fine so far : )
Thanks for the naked egg experiment…am trying this as we speak
this gave me an idea…can food coloring be absorbed if added to a cup of water in the fridge then be used to cook?
That’s an interesting idea, you should give it a try and report back what happens. I would suspect that it may be hard for the coloring to make it through the egg shell, but give it a try!
I’ve had a square egg maker for a long time! Hardboil an egg, peel it while still hot and immediately put it in this little plastic contraption to cool. It is a plastic square box with removable top – put the egg in, replace the top and screw it down a bit so it exerts a little pressure. Voila! Square egg! I know, totally useless, but fun for the grandkids!!
It was neat to read about this. When I was a child, my mother worked at a local egg farm and on occassion would bring home naturally naked eggs. They were rare but every once in a while a hen would lay an egg whose shell did not harden properly. Since they couldn’t package and sell these eggs, she would bring them home to us. Neat to know I can re-live childhood through science!
Just did this with my crew and they loved it!
Try letting the kids put their fingers in the corn syrup before and after the egg. After the egg has ‘deflated’ you can tell that all of the water that was on the inside of the egg is now sort of on top of the syrup. This helped my crew (4 yrs- 9yrs) actually realize that the water inside the egg didn’t just disappear.
Thanks Jennifer, “fingers in the syrup” is a nice way to show that the water didn’t just disappear.
This is a great way and simple to teach children about osmosis and reactions. Thank you for the great experiment