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I have purchased a Nutri-Q 34360 Healthy Eating Egg Boiler:

How does it work? - The eggs are cooked through hot steam. The instructions will guide you on the amount of water that is required depending on the quantity of eggs.

It comes with a little measuring cylinder for the amount of water to add which has gradations that look something like:

Hard boiled
- 1
- 2
- 3
- 4
- 5
- 6/7

Medium
- 1
- 2
- 3
- 4
- 5
- 6/7

Soft
- 1
- 2
- 3
- 4
- 5
- 6/7

I understand why more water is required to hard boil eggs compared to medium cooked eggs (they need to be cooked longer).

However, I don't understand the gradations within each range (the number of eggs to be cooked).

Why does, for example, cooking 1 medium egg require more steam than cooking 3 medium eggs? Surely it should be the other way around?

Can someone enlighten me?

Photo of the parts:

enter image description here

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  • 2
    probably because with one or 2 eggs, there needs to be more steam to fill the space ? – Max Jun 13 at 11:58
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    @AJN there is only an on/off switch. Nothing to indicate number of eggs. And it turns off by itslef. – DavidPostill Jun 13 at 13:41
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    Similar question over on Physics SE: physics.stackexchange.com/questions/429363/… – BowlOfRed Jun 13 at 20:26
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    Wouldn't it be a simple matter of displacement? The more space taken up by eggs, the less room there is for water - if you used the same amount of water for 6 eggs as you used for 1, it would overflow... – Darrel Hoffman Jun 14 at 15:30
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    @J... because it makes life easier? Like pretty much everything in life. I have a toaster because it’s easier than lighting a fire and holding my toast on a fork. I have a microwave because it’s faster to cook ready-meals than the oven. I have a hot water dispenser because it controls the temperature for different drinks. Telling people what they should or shouldn’t spend money on, or use their counter space for, is probably not going to improve anyone’s insecurities about cooking (it certainly wouldn’t help mine!) – Tim Jun 15 at 9:20
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These egg cookers work by simply heating the water until it all evaporates. Most cookers sense when all the water is evaporated, and automatically turn off and/or alerting with a beep or noise. They have a sensor under the hot plate that detects temperature. When water is still in the pan, it keeps the pan cool, and when water evaporates completely the pan bottom will start to get hotter.

The water is heated in the pan in the bottom, works it way past the eggs, and eventually out the holes in the lid.

So why more water for fewer eggs?

The tray that holds the eggs has a bunch of holes in it. Each egg cup has a hole in the bottom so that the steam has direct contact with the bottom of the egg. When the tray is full, it reduces the number of outlets and traps more steam under the tray. Similar to putting a lid on a pot, this reduces the speed of evaporation.

With only one egg blocking one hole, the steam can escape more readily out from the bottom of the tray to the top, and steam will escape out into the room more quickly.

To compensate for the fact that steam is escaping the egg cooker slightly faster when there are fewer eggs, you use slightly more water when there are fewer eggs.

A fun experiment

You could use eggs (or a heat proof substitute... Maybe something ping pong ball or golf ball sized (but not ping pong balls--they melt at 80°C)) to block off the "egg holes" and collect a series of timings for how long it takes for all the water to evaporate as you vary the number of eggs & water.

You should find that when you follow package directions, the timing of the cycle is approximately the same.

Similarly, if you use only one egg, and the "6/7 egg" water amount, you'll find the cycle (and complete water evaporation) faster than the full "1 egg" water amount. Again, this is just because there's an easier path for the steam to escape.

7
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    This looks like a likely explanation and it makes sense, thanks. I only eat boiled eggs once per week, but I will try some tests hopefully and come back with some results when I'm able. – DavidPostill Jun 13 at 16:10
  • As it's very hot at the moment and I'm eating a lot of salads I may experiment with cooking different numbers of hard boiled eggs that I should be able to keep in the fridge for a few days and time the cooking. Normally I eat 3 soft boiled eggs once per week. – DavidPostill Jun 13 at 16:14
  • Ah! This makes a lot more sense than my guess. I had not noticed that there were vents in the top of the device to allow steam to escape. – Xander Henderson Jun 13 at 18:19
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    Ping pong balls are clearly not what I would qualify as "heat-proof"! – Xi'an Jun 14 at 8:18
2

The volume of space within the container (that must be filled with steam) is less with 6 eggs (258 ml) than with 1 egg (43 ml).

Therefore you must produce more steam (thus need more water) for 1 egg than for 6 eggs to have the same effect.


Sample:

The container, after the water and egg holder, has a volume of 500ml.

Each egg has a volume of 50 ml.

For 1 egg, 450ml of steam is needed (50+450=500ml)
For 3 eggs, 350ml of steam is needed (150+350=500ml)
For 6 eggs, 200ml of steam is needed (300+200=500ml)

The water needed for 200ml of steam (for 6 eggs) is less than the water needed for 450ml of steam (for 1 egg).

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