The temperature jump at the bottom of the pot
A basic rice cooker does not measure how much water remains. It senses the temperature of the cooking pot, usually through a thermostat beneath the inner pot. While liquid water is present, heat goes into warming it and turning it to steam. The pot’s temperature therefore stays close to water’s boiling point rather than climbing freely.
Once most of the water has evaporated or been absorbed by the rice, that cooling effect fades. The pot’s bottom can then heat up quickly, rising above the boiling-temperature plateau. That sudden rise—not a timer or a direct water-level reading—is the signal to stop cooking.
A simple switch, not a rice-reading computer
In many traditional cookers, the thermostat operates a spring-loaded switch. As the temperature crosses its set point, the mechanism releases the switch, cutting power to the main heating mode. Some models then shift to a lower “keep warm” setting; more advanced cookers may use electronic sensors and more elaborate controls.
Because the trigger depends on the pot heating up, the cooker can respond to different amounts of rice and water without needing to know the recipe. But it is not judging whether the rice is perfectly tender. It is detecting a physical change that usually occurs when free water is gone. The same change explains why a cooker can keep cooking if it is opened or has too much water, and why adding too little water can make it switch off before the rice is done.
