[ELI5] How does a rice cooker “know” the timing to switch from cook to warm when there’s no more water in it?

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[ELI5] How does a rice cooker “know” the timing to switch from cook to warm when there’s no more water in it?

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The rice cooker will heat the bowl. The water will absorb this heat and turn to steam, which the rice absorbs. Once there’s no more water left to absorb the heat, the bowl will quickly rise in temperature. Sensors in the rice cooker will detect this jump in temperature and switch off or switch to keep warm mode.

While there is water the temperature will never exceed the boiling temp of water. This is the natural of boiling water (or anything) when you boil water the water *can not* get hotter then the boiling point until it has infact completely boiled.
This is one reason a lot of recipes will tell you to bring water to a boil. It’s an easy way to make sure you cook at a specific temperature. You totally could cook pasta at a lower temp. But good luck getting the timing right without a thermometer and constantly adjusting the temp.

Once all the water has boiled away the temperate will rise and the rice cooker knows to shut off. There are a lot of different types of temperature sensors so I cant tell you which ones a given model uses.

Honestly rice cookers are one of the coolest devices because of how deceptively simple they are.

There is a thermometer that senses when the water has fully boiled away. The presence of water keeps the temperature at the boiling point. Once the water is gone the temperature rises, tripping the internal thermostat to switch from boil, to keep warm

Technology Connections on YouTube has a video that does a great job of concisely explaining how they work.

https://youtu.be/RSTNhvDGbYI

The classic/cheap rice cookers use a magnet to keep the electrical switch closed in the “Cooking” position.

The magnet heats with whatever is in the bowl.
As long as there is water, the temperature will stay at a maximum of 100°C (at sea level).
Once the water has evaporated, the temperature while rise above 100°C.

The magnet is made to loose its magnetic properties just above 100°C and it will release the switch back to the “Warm”.