HN Theater @HNTheaterMonth

It's a great channel. I was also fascinated by his rice cooker episode. I had no idea they were so clever, combining thermodynamics and the physics of magnetism.

https://www.youtube.com/watch?v=RSTNhvDGbYI

I have a basic rice cooker and I absolutely love it. Perfect rice every time without having to think too hard about measurements or the time, as the measurements are stamped on the bowl (fill rice here, fill water here) and it will always switch to warming mode at exactly the right time. I wouldn't bother getting a fancy computerized model, the old thermostatic ones are pretty much perfect.

Technology Connections video on old-style rice cookers: https://www.youtube.com/watch?v=RSTNhvDGbYI

We have that exact same kettle, its wonderful.

⬐ greenonions

My wife convinced me to buy what I would consider an expensive rice cooker, computerized. Now the rice is fantastic, I'll admit. However, I'm not really convinced that it's worth 6x a basic rice cooker.

I started using the old-fashioned analogue rice cooker after watching Technology Connection's video on how they work.

The principle is clever: liquids at boiling point stay at boiling point, since any additional heat energy is used to change their state from liquid to gas. When the temperature does rise above 100°C, that means there is no liquid left in the cooker, and so rice must be done. It then switches off the high heat and runs in "warm" mode.

1. https://www.youtube.com/watch?v=RSTNhvDGbYI

⬐ dehrmann

It's more clever than just this, though. My Zojirushi rice cooker has a timer, so it seems to know how far along the process is and speed it up...or it lies, pads the cook time by 10 min, and keeps it warm.

The science behind a rice cooker is fascinatingly clever, yet painfully simple.

In short, boiling water temperature plateaus due to the latent heat of vaporization. When the water is gone the temperature of the pot starts to rise. The rice cooker uses this principle to control the switch. The switch is held by magnet. When the pot finishes boiling the heat rises and exceeds the curie point of the magnet, which means the magnet ceases to be magnetic, and the (no longer) magnetic switch is released turning the rice cooker off.

Here’s a great video explaining how it works.

https://youtu.be/RSTNhvDGbYI

⬐ jrootabega

It's not the magnet's curie point; it's the curie point of the metal the magnet sticks to.

And I guess it's not really the curie point, just the point where the force becomes weaker than the spring

⬐ throwaway_pdp09

That sounds wrong. From wiki "In physics and materials science, the Curie temperature (TC), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties". What you're saying is that metals stop being attracted to magnets above a certain, rather low temperature. Possible but very hard for me to imagine.

⬐ vincnetas

Thats exactly whats happening. If magnet was to loose its magnetic properties, you would have one time use cooker with permanent "non magnet" ofter first batch. Metal above certain temperature also is not attracted by magnet.

⬐ throwaway_pdp09

Thanks @amluto, @vincnetas. I really didn't know that.

⬐ amluto

If you take a permanent magnet, heat it above the Curie point, then cool it again, it’s no longer magnetized. So you would have a one-use rice cooker.

Magnets stick well to ferromagnetic materials. If you heat a ferromagnetic object, e.g. a piece of steel, above Tc, it stops being a ferromagnet and magnets will stick to it much less firmly. And, when you cool it, it will once again be ferromagnetic.

⬐ smnscu

I knew it would be a video from that channel, haha. I discovered it recently and it's a treasure trove of fascinating, "How It's Made"-on-crack technology videos. Link for the lazy: https://www.youtube.com/channel/UCy0tKL1T7wFoYcxCe0xjN6Q

⬐ spaceflunky

They’re funny videos because you’re like “man I can’t stand this guy’s cheesy jokes” cut to 12 videos later “I CANT WAIT TO SEE WHAT HE DOES NEXT!!!”

⬐ jrimbault

It's basically the same physics involved in this toaster https://youtu.be/1OfxlSG6q5Y same channel.

Thing heats and deforms (change properties), when it reaches temperature n, thing deforms just a bit too much, cuts electrical contact.

⬐ bch

These are both clever, but different physics. The toaster uses metallic elasticity (and a subsequent distortion) due to heat, and the rice cooker uses the heat-induced disappearance of magnetism to disengage a switch.

(I have one of those toasters, and they’re very pretty and charming to see work.)

⬐ jhallenworld

>In short, boiling water temperature plateaus due to the latent heat of vaporization. When the water is gone the temperature of the pot starts to rise. The rice cooker uses this principle to control the switch.

This is true for a lot of appliances: water boiler, coffee percolator, drip coffee maker, etc. They have to be reliable enough that you can have a 1000W+ heater right next ABS plastic and not have problems with millions of units.

⬐ throw0101a

> When the water is gone the temperature of the pot starts to rise.

Water-to-rice ratios are important. America's Test Kitchen has a good video on the topic, especially if you're using a pot and not a rice cooker:

* https://www.youtube.com/watch?v=JOOSikanIlI

* https://www.youtube.com/watch?v=DJFU7ezipbg

The rice actually only 'needs' a 1:1 ratio, but you need to put in extra to deal with evaporation; brown rice needs more-extra because it takes longer to cook (the bran slows absorption), and the longer cooking time leads to more evaporation.

TL;DR: ignore what's on the bag/box, and for every cup of rice add one cup of water (1:1, 2:2, 3:3), and then a fixed amount of extra overhead for evaporation.

⬐ dogma1138

Rinsing the rice and letting it sit for 30-60min absorbing some moisture then a 1:1.25 ratio is by far the best method I’ve used.

I also let it steam in its own heat for the last 10min or so of cooking since the temp won’t rise it won’t overcook the rice but it will prevent any rice from being undercooked or from the rice at the bottom form burning.

If I don’t have the tome to rinse I usually increase the ratio slightly and cook it for 5min longer and let it sit covered for 5 additional minutes but the result will also be a much more stickier and starchy rice.

People also for some reason stir rice which you should never do unless you are making glue or rice pudding (which tbh is the same recipe minus the sugar and flavorings).

⬐ hantusk

Also, don't add salt until the process is finished, as that also makes it more starchy

⬐ thiht

That's not right. Jasmine rice for instance requires more like 1,5:1 water, at least (you can go up to 1,75 for extra softness). And for what it's worth, it's what is written on the bags I buy.

⬐ throw0101a

> Jasmine rice for instance requires more like 1,5:1 water, at least (you can go up to 1,75 for extra softness).

ATK mentions various types of rice that they experimented with; there doesn't seem to be anything special about jasmine:

> We gathered 17 different varieties of rice, including white and brown short-grain, medium-grain, long-grain, basmati, and jasmine [!!!!] rice plus two varieties of red and black rice. After rinsing the rice to remove excess surface starch, we placed 1 cup of each type with 1 cup of water in a vacuum bag and sealed them to ensure that no water could evaporate during cooking. […]

> To the surprise of our tasting panel, every variety of rice was properly cooked using the 1:1 ratio of rice to water. All of the rice types were tender throughout with no chalky or mushy grains. In addition, the water had been completely absorbed in each sample.

* https://www.cooksillustrated.com/articles/1692-nailing-the-p...

You can easily re-create their experiment: buy a bunch of rice, put them in sealed bags with water, completely seal the bags, and cook them sous vide. Cook one bag of jasmine at 1:1, one at 1.5:1, 1.75:1, etc.

The statements are falsifiable / confirmable.

Again: long/medium grain rice has 1.5:1 recommended, and brown rice 2:1, because of longer cooking times—which allows for more evaporation to occur. The rice itself only needs 1:1, anything else is about factoring evaporation which is fixed regards of quantity being cooked.

So when measuring out: do 1:1 for the cups of rice, and then add the extra needed for your particular pot-stove combination.

⬐ gbear605

The traditional method in a lot of Asia (per what I’ve read online) is to put a finger on top of the rice pointing down, so that your fingernail is touching the rice, and to fill water up to your knuckle.

⬐ badfrog

That's covered in the first video link

⬐ jlokier

That sounds useful, thanks.

But which knuckle?

⬐ yissp

Wouldn't this result in different amounts of water depending on the dimensions of the pot?

⬐ throw0101a

ATK recommends settling on one pot, which can perhaps accommodate various needed sizes, that way you have a consistent amount of evaporation.

If you use different pots, with lids of perhaps different levels of sealing, then your results will be all over the place. If you always use the same 2-3 qt/L pot, you'll always get the same evaporation.

⬐ tzs

Evaporation rate should be proportional to surface area, so the volume of extra water you need to add to make up for that should also be proportional to the surface area too. Adding extra water to a fixed depth accomplishes that.

This is assuming a pot with straight sides, at least above the lowest water level during cooking.

⬐ wtvanhest

Ah, I always wondered why that worked. I fought against it for a while, then started using that method out of laziness, but it works so well, I don’t use another method now.

⬐ ValentineC

Thanks for the explanation. As an Asian, I've never quite figured out how it seems to work out until now, and was confused when the BBC suggested a 1:2 ratio of rice and water [1].

[1] https://www.youtube.com/watch?v=iUgOz5emQ94

⬐ totetsu

I was half expecting to see this link https://www.youtube.com/watch?v=6pPb9mPzoXs

⬐ None

None

⬐ firethief

> Evaporation rate should be proportional to surface area, so the volume of extra water you need to add to make up for that should also be proportional to the surface area too.

This would be accurate at room temperature, but under stovetop conditions wouldn't evaporation rate be determined mostly by the amount of heat energy added to the water?

⬐ tzs

The evaporation rate per unit area would depend on many factors, including temperature, how much water is in the atmosphere, pressure, probably what is in the water, and surely a host of other factors.

The evaporation rate from the pot as a whole at any given time will then be that rate per unit area, which depends on that host of factors, times the surface area.

So once you know how deep a layer of extra water you need to add to cover evaporation in one pot, that will be the same depth of water you need to add to a different size pot if you are cooking in that different sized pot at the same temperature, pressure, etc. as the first pot.

Think of it this way: Imagine you have a rectangular pot, with a removable divider in the middle that effectively turns it into two smaller pots side by side.

If you put the divider in and cook some rice in the left side, you need a certain depth of extra water. If instead you cooked that rice in the right side, you'd need the same depth of water there.

Now imagine cooking in both sides simultaneously. You'd still need the same depth in each side as when you were cooking in that side solo.

OK, now imagine cooking in both sides, but without the divider installed. That's not really any different than with the divider installed. Each side is still going to need the same depth of water as before.

(Well, there will be some difference. Not all heat gets into what you are cooking through the bottom of the pan. The sides get hot too, and some heat comes in that way. Remember that the evaporation rate at any given point on the surface depends on conditions at that point. A spot in the center will take longer to reach a given temperature than a spot near a side, and so we'll have a non-uniform evaporation rate across the surface. I don't think this will make much difference as far as rice cooking goes, but figuring out for sure would require knowing a lot more about how heat moves within a batch of cooking rice than I do).

⬐ cma

And altitude.

⬐ folknor

Both, and more.

In my experience, the surface area where evaporation occurs has the most impact. If I know (and obviously I do every time, just measure it) the evaporation area size, that's what I use to dial in how much pre-boil wort I need the first few times I use a set of equipment.

But heat energy is the second most important factor. Sea level, salt/mineral levels, and other factors are - in my experience - not worth considering. But I've not tried to brew beer on the top of a mountain.

I've brewed over 300 batches of beer in vessels of various dimensions (including surface area and evaporation area), and with various amounts of heat energy, applied in various places in the vessel. Ranging from 2kW to 18kW, sometimes heat applied under the pot, sometimes distributed throughout for example 3 heating elements at various heights. 2kW for all from 15L to 60L vessels, 6-18kW from 25L to 120L, and 18kW (IIRC) for 500-800L.

When brewing beer, the boil usually lasts for 60-90 minutes, and the boil off rate is extremely important for hitting your target gravity and volume, and getting a consistent result if you're brewing the same recipe again.

What you do as a brewer is you test the equipment on the first 2-3 batches and then after that you can hit your target boil-off with 99% accuracy every time, or 100% in an enterprise-grade professional setup.

I've never been more than 5-10% off my estimated boil-off rate for the first batch, and I only account for surface area in that estimate. Even with 6kW for 25L.

Have I got the channel for you! Technology Connections: https://www.youtube.com/channel/UCy0tKL1T7wFoYcxCe0xjN6Q . My introduction was his rice-cooker video: https://www.youtube.com/watch?v=RSTNhvDGbYI .

⬐ agumonkey

I binged his videos quite a lot already. Very nice right ?

Probably meaning one without a microcomputer.

https://www.youtube.com/watch?v=RSTNhvDGbYI