I am disappointed by America’s Test Kitchen Podcast. Not deeply, but slightly.
Listening to a few back-episodes there was a brief mention that the problem of making hard-boiled eggs that peel perfectly “is not understood.” These are the people who do experiments on all kinds of stuff – but perhaps the experiments they do in the test kitchen are all just a cover-project for eating lots of cake and spare ribs, or something.
After tackling this problem using science I wrote ATK a quick explanation, but I’m sure they don’t care. Because, if they did, they would have done some thinking and figured it out themselves. For the record: I don’t care either. I eat a lot of hard-boiled eggs, so it was an easy experiment to perform.
Good science would entail establishing a theoretical framework that matches everything we observe without any contradictions, then an experiment is devised that adds additional potentially contradicting evidence. We present the evidence and our theory, then conclude by eating breakfast.
- When eggs are put in boiling water as it’s coming to a boil, very small bubbles often come from the egg. These are not the result of steam (“rolling boil”) in the pan, they originate apparently on the egg itself.
- The surface of eggs appears to be slightly porous.
- Inside the egg there is a thick sort of rind layer, then the white and yolk. The rind can sometimes hold together a slightly cracked egg.
- In many eggs I have successfully and easily peeled, the rind is the dividing-point between the white and the shell/rind; i.e.: it peels cleanly with the rind.
- Baby chicks grow in eggs. There’s probably some way for them to get air.
- The America’s Test Kitchen people said that older eggs hard boil better. ( <- this is apocryphal information not evidence)
- Peeled eggs, when placed in water, do not dissolve – they remain hard and retain their shape.
We hypothesize that:
- The shell of an egg is porous. The white of a cooked egg is not porous. The rind must be porous or the chick would die in the egg.
- That air gets driven out of the egg means that it expands when heated (of course) and the contents of the egg may also expand slightly, driving out the air. That explains the little bubbles.
- As the egg cooks, the air gets forced out. As it cools, stuff gets sucked back in. If that stuff is air, it’s easier for the rind to stick to the cooked proteins of the white. If that stuff is water, it gets sucked back in and keeps the rind and the protein from binding thanks to a thin layer of water between the now-cooked sticky proteins of the white and the rind.
- If older eggs have dehydrated slightly (since the shell is porous) there will be more air in the egg, so older eggs will suck back in more water when they cool; they may peel more easily.
- Boil an egg 5 minutes. Observe tiny bubbles
- Leaving eggs completely immersed in water, flush the pan with cool water containing food dye
- Allow the eggs to cool, with an additional flush of dyed water
- After 3 minutes, rinse outside of eggs with clear water
- Rinse hands, pan, etc, with clear water
- Place eggs on white paper towel (for visual contrast)
- Test peeling the eggs – do they peel easily Y/N?
- Observe whether there is food colorant inside the egg’s shell as it is peeled
How to make easy-peel hard boiled eggs:
- Cover eggs in cool water
- On low/mid heat and bring slowly to a boil
- Boil gently for 5 minutes
- Without dumping the water – keeping the eggs completely covered with water at all times – place the pan under tap and run cold water until the pan and water the eggs are in is cold
- Let sit 4 minutes
- Peel the eggs
Our hypothesis appears to be confirmed, at least to the degree that: there was green dye inside the egg’s shell and on the white, which indicates that the dyed water went into the shell before it was broken and that the shell and membrane are porous.
I believe this also explains why eggs that have slightly cracked shells are sometimes easy and sometimes very hard to peel: the easy ones are the ones where water gets into the rind and the eggs cook with the water separating the rind from the white, the hard ones are the ones where the water doesn’t get sucked back in as the eggs cool, because the shell is compromised.
This batch of eggs peeled easily. They tasted great.
I cannot claim that this applies to all eggs by induction, but I have been making all my hard boiled eggs this way for about a year, now, and I have only had trouble on the occasions where I am too impatient to let the eggs cool sufficiently under the water.
I never got to do school science fairs. Can you tell?