I don’t know about you, but I find cooking rice to be an extremely difficult task.
Luckily somebody invented the automatic rice cooker
and now all of my rice cooking problems have been solved!
Hooray!
Now, you might think that rice cookers are a pretty boring small kitchen appliance.
But actually, they’re among the...
well, OK...
If we’re looking at what they *do* then yeah, heh
this ain’t no toaster, that’s for sure!
But, while the device itself may seem pretty unremarkable,
and indeed is,
the principle by which it works is fascinating!
Simply by exploiting one of the chemical properties of water,
this device can tell when the rice has been cooked, and the result is a
perfectly cooked batch of the world’s second favorite grain.
Assuming you got the water to rice ratio correct, that is.
So how does it work?
Well, to find out, first we need to learn a little bit about water.
As I’m sure we all know, at sea level water boils at 212 degrees Fahrenheit.
Isn’t that just a delightfully easy number to remember?
I don’t know what the heck that is in Celsius, probably some silly arbitrary thing,
but anyway that number isn’t the whole story.
You see, water doesn’t just boil at that temperature.
It *starts* to boil.
See, if you got a pot of water on the stove, and
you watch its temperature rise with a thermometer,
well what do you suppose happens once it gets to boiling point?
You can see the temperature steadily rising as it approaches,
so you might think that once it hits boiling point the water will just
*poof*
disappear and turn into a big 'ol cloud of water vapor.
But of course, that’s not what happens.
The temperature just plateaus, and it won’t go any higher.
But the stove
(or hot plate)
is still dumping energy into the water, so why isn’t it getting any hotter?
The answer is physics, and more specifically the principle known as the latent heat of vaporization.
This is a fun concept important to many fields of study, from meteorology to refrigeration.
Also known as enthalpy of vaporization, this is the amount of energy required to transition
a liquid into a gas.
And it’s a LOT more energy than just raising the temperature of that liquid
(boiling of water starts to becomes audible) OK, what we need to understand here is how
latent heat differs from sensible heat.
Sensible heat is something like, oh I dunno 68 degrees?
That's a a pretty sensible room temperature--
Ohhh, oh, Sensible,
like can be sensed. Got it. (though it is still spelled "sensible")
Sensible heat is the figure we can sense, or measure.
The thermometer is looking at the sensible heat when it tells us how hot something is.
But as the water (or any other substance) reaches its phase change temperature, adding energy
into it will not raise the sensible heat.
Instead, that energy gets absorbed by the
molecules to free them from their liquid state, and that takes a heckuva lotta energy.
(boiling gets louder) We don’t need to be too worried about that
extra energy right now.
We’ll get to that when we tackle air conditioning and refrigeration.
But what you need to know for the purposes of cooking rice
is that liquid water cannot exist at a temperature higher than its boiling point.
Dumping more energy into it will simply make it boil away faster.
It will not make it get any hotter.
So what does that have to do with cooking rice? Well, see, cooking rice is all about
making water hot so that the rice will absorb it and the starches convert to the other...
things and all that jazz.
And that rice is cooked once it has absorbed all the water.
You don’t want to keep cooking it after that point or it will burn, and you don’t want to not
cook it long enough or you’ll have rice al dente which I’m pretty sure isn’t actually a thing.
So, in an ideal world, we’d have a way to tell precisely when that rice has finished cooking.
And, thanks to latent heat of vaporization, we do!
See, water can’t get hotter than its boiling point.
But cooked rice can.
And once you know that little factoid, you can easily make a device which will cook rice
to completion, and automatically stop.
This is a very basic rice cooker.
It cooks rice...
and that’s it.
None of that fancy multi-function nonsense.
Side-note -
I actually have a nicer rice cooker with a whole electronic interface
thing that can do fancy things like slow cook or steam vegetables but it’s got one of
those gasket deals going on in the lid and frankly it gets really gross all the time.
And it’s a pain to clean.
Now I’m not certainly someone who eats rice as a staple food but when I
discovered that this cheap, basic unit had just a plain glass lid and both it and the
bowl are dishwasher safe, I was like “Life Changer!” and bought it on the spot.
Truthfully I prefer it to my fancier one by a large margin simply because it doesn’t get gross and it cooks
rice just as well, which is all I use a rice cooker for anyway.
Plus it doesn’t beep incessantly for 15 seconds when it’s done, so that’s a nice plus.
Sometimes basic is in fact better, but that’s all down to your personal priorities and preferences,
and I’m sure you all tell me why my priorities and preferences are wrong!
Anyway, this device is so incredibly simple and yet entirely automatic and I just love that sort of thing.
At the bottom, you’ve got a round heating element with a little
button thing poking up through the center.
This guy is spring-loaded and is the heart of its automatic operation.
The rice cooker has two modes: Cooking, and keep warm.
Whenever it’s plugged in it’s in the warming mode.
If we flip it over and take off the bottom, we’ll see that there’s a buncha wires.
In the keep-warm state, current comes in through the power cord, and passes through this big
resistor to limit the current before going through the heating element. The lever to
engage cooking is attached to that button thing, and importantly it closes these contacts.
This bypasses the resistor and allows the heating element to run at full power.
In this case, it’s a mere 300 watts.
This is after all a tiny little rice cooker.
Also, this changes which of the little neon indicators lights up.
Useful!
You’ll see that right now I cannot get the lever to stay engaged.
That’s because the button thing isn’t depressed.
This serves as a safety feature to prevent the heating element
from operating at full power if the pot were to be removed.
Ordinarily the weight of the bowl would press down on it,
but in this case I need to substitute my fingers.
With it depressed, you’ll see that the lever will now stick in the down position.
What’s keeping it there is a permanent magnet, which you can just barely see here.
And this is where things get really interesting.
The magnet is sticking to the bottom of the button,
and it’s overcoming the force of a second spring inside the button trying to push it away.
Which, luckily, it manages to do.
But here’s the thing about magnets.
Get things hot, and suddenly magnets don’t work anymore.
Uh-oh here comes a Blanket Statement Abatement Alert!
Magnets are confusing.
Ferromagnetism.
Paramagnetism.
Curie points.
There’s just so much that hurts my brain.
So, please do not assume I’m an expert here, ‘cause I’m not.
Regarding this magnetic phenomenon I’m about to describe,
this is my very best interpretation from what I’ve uncovered through looking
at patents, a very rudimentary understanding of magnetic interaction, and also some forum
threads where people were arguing about this.
If I’ve gotten something wrong here, please correct me in the comments.
And also, please check to see if someone else has already provided a correction,
thanks.
All magnetic materials have what’s called a Curie temperature, or Curie point.
For ordinary ferromagnetic materials, once you reach this temperature they cease to be ferromagnetic at all.
In the case of a permanent magnet, if you get it to the Curie temperature ...
you’ve broken the magnet permanently.
So now it’s a permanent not-magnet.
But materials that are attracted to permanent magnets
will regain their attraction once they’ve cooled back down.
This button thing is made of an alloy that has a Curie temperature just a bit higher
than the boiling point of water.
This allows it to function as a temperature-dependent kill switch.
Thanks to the outer spring, it’s always held firmly in contact with the bottom of the pot,
which ensures it and the pot are at nearly equal temperatures.
So long as there’s liquid water sitting in that pot, the pot itself cannot get hotter than water's boiling point.
This means that the button remains magnetic, and the magnet is able to overcome
the force of the inner spring, so the device stays in cook mode
But, once the rice has absorbed all of the water
(and / or once all the remaining water has boiled away)
the energy being added to the pot by the heating element is no longer being absorbed as latent heat.
Now, the pot can quickly start to exceed the boiling point of water.
And once it gets past the Curie point of that little sensing button,
the magnet is no longer attracted to it, so the spring overcomes the magnet and...
*click* the rice cooker switches back to the warming mode.
Now, I don’t know about you, but I think this is some of the most amazing ingenuity
out there.
This incredibly basic device is not only exploting the physical properties of water,
but also the physical properties of magnetism to automate the cooking of rice in an elegant
and effective way.
Sure, my fancier rice cooker may have some fuzzy logic and a microcontroller
in there, but anybody can program an Arduino with some inputs and outputs.
So this is much more interesting, at least I think so.
These days, only the most basic rice cookers continue to use this method of automation.
But, for decades this is just how rice cookers worked.
I’ve tried to find when exactly this method was first put into production,
and short of looking through every rice cooker related patent out there,
the answer isn’t obvious.
However, it’s been in use at least since the late seventies, having come across this patent.
And you might be surprised to learn that rice cookers are a rather recent invention.
When you consider that we’ve had mechanical refrigeration for over a century now,
it can seem a little weird that it took until 1956 for the first automated rice cooker to appear on sale in
Japan, produced by Toshiba.
Those early rice cookers used a sort of double boiler to indirectly heat the pot.
Everyone’s favorite source of knowledge claims that that went out of style
in the 1960’s but, citation needed.
Anyway. That’s it!
I hope you enjoyed this video.
While I wouldn’t necessarily call this device Automatic Beyond Belief!
it is certainly among the most clever forms of automation out there.
Even if I have to push the lever down.
And of course, thanks to everyone supporting the channel on Patreon,
with a special thanks going to these nifty people scrolling up your screen.
CED part 5 is coming soon, so be on the lookout for it!
For now, though...
eat up!
♫ insensibly smooth jazz ♫
I don’t know about you, but I find …
the teleprompter to be a little finicky today
Their among… well ok,
if we’re looking at they d ..
yeah no I don’t like THAT take
So, in an ideal world,
( makes weird noises as he checks his shirt )
So, in an ideal world…
It cooks rice. And that’s it.
None of this … pbbbbttptt
But, once the rice has absorbed .. bleuw
I just noticed an error.
We’ll try to fix it
Materials that are attracted to permanent
magnets will regain …
pbbpbpbppb (this one was excessive)
Hey, it's me! The SPIRIT OF THE CREDITS!
Usually, I'm the SPIRIT OF THE ENDSCREEN but the shoot went real well and there aren't many bloopers.
So now you get to spend more time with ME!!!
And I'm here to tell you that you're a pretty cool human!
Well, and I suppose there could be some non-humans watching, too. You're all cool!
Oh, wait, but y'all need to be able to read to see this part.
Does that mean the SPIRIT OF THE ENDSCREEN can't talk to animals?
Goodness isn't this an existential crisis?
And so is reaching the end!
AUGH!!