Dissolving an egg shell
Dave Ansell and Adam Murphy celebrate Easter with this egg-cellent egg experiment...
Dave - For this demo you need an egg, some vinegar, ideally malt vinegar - something really quite strong - and a jar with a lid on it.
Adam - I've got my egg, I've got my vinegar and I've got a jar. So Dave, how do we go about putting together this eggs-periment?
Dave - Very good. First of all, you want to take some vinegar and pour it into the jar. I happen to have a gallon of vinegar here for some reason. So I'll pour this in.
Adam - I do not have a gallon, but I'll pour in what I've got.
Dave - You want enough in there so the egg is completely covered. But not so much that you're gonna get vinegar all over the table when you put an egg in it. Take your egg and lower it gently into the jar, ideally without breaking it. Then put the lid on loosely - not too tightly because you might get some gas given off in this reaction. Oo, looking at my egg now, it's covered in little tiny bubbles. These should be carbon dioxide because the egg shell is made of calcium carbonate, same stuff as limestone. And that will react with the vinegar to create a salt and carbon dioxide which is coming off as bubbles.
Adam - Is this process just like pickling eggs? Like you'd buy pickled eggs in a chip shop?
Dave - Not quite the same although it has some similar properties. Normally when you pickle something, you would cook it first, which will break down all of the cells and make it a lot easier for the vinegar to diffuse into the middle and basically fill the whole thing with vinegar, which will kill any bacteria in there, so preserve it. You also kill the bacteria by cooking it, which is useful. We're also not giving this early long enough to fully pickle it. So maybe the outside edge of the egg will end up pickled, but the middle of it won't have enough time to be pickled properly. And then leave it for a few hours or probably better overnight and we'll have a look at it then.
Katie - This is where the patience comes in. But, rest assured, Adam and Dave have plenty of time on their hands!
Adam - Right, so it has been three days roughly since I put my egg in a jar of vinegar. Unfortunately my egg has lost integrity and there's now just a fairly disgusting puddle sitting in jar. Dave, have you had any better luck than me?
Dave - My egg, it looks, it's still egg shaped. It's covered in some bubbles. I think it's probably grown a little bit bigger than it was before. I'll just pour it out of the jar into a bowl. And it doesn't have a shell on it at all. It's kind of slightly squishy. It was a brown egg with a sort of filmy membrane, which is floating around it. And if I hold it up to the light, you can just, it's sort of a translucent ball, you can just about see where the yolk is floating around inside.
Adam - When you say it's grown a bit, what do you mean by that?
Dave - Now, instead of being covered by a hard shell, the hard shell has dissolved in the vinegar. It's just covered in that kind of membrane, which you get just underneath the shell of an egg. And that's kind of rubbery. And so I think what's happened is that osmosis - there's a process called osmosis, which means liquid will tend to go from less concentrated areas to more concentrated areas, so water's moved into the egg and it swelled up slightly. So it feels taught inside. It's very, very rigid, like a full balloon. Yeah. Basically it feels like a balloon full of egg.
Adam - So what's actually happened to it? Why is it turned from an egg to a balloon full of egg?
Dave - The balloon was always inside the egg. It's that membrane which you find if you're eating a boiled egg, and it tends to stick inside the shell, but the vinegar has just dissolved away the hard shell leaving that membrane and it swelled up a bit, do to osmosis.
Adam - And then do you have any ideas about why yours worked so well and mine disintegrated?
Dave - Did you use a very cheap egg Adam?
Adam - It wasn't, it wasn't top shelf, let's put it that way.
Dave - My guess is that whereas mine was actually quite a good quality free range egg. My guess is that large healthy chickens will probably have more resources to spare to make a nice big strong membrane around the outside of their eggs. Whereas slightly unhealthy battery chickens probably put less effort into it. And so the eggs are less robust. It's definitely true of the thickness of the shell, so I don't see why it wouldn't be true of the membrane as well.
Adam - Would you be willing to eat this egg?
Dave - There's no fundamental reason not to. I imagine it will taste very strongly of vinegar, but I'd want to cook it first.
Adam - Yeah. I think I'd want to do that. I think otherwise it would be a hard no from me.