How does the microwave popcorn button work?

Answer 1

Most microwaves cook at a single power output (though these outputs vary by wattage), varying the amount of microwave radiation by turning the magnetron (the device that actually produces the microwaves) on and off for varying lengths of time, depending on the power setting you enter before you start cooking.

That said, the microwave button on these microwaves generally just sets the microwave for a pre-programmed length of time--usually around 2:20. It will then cook your popcorn at 100% power for 2 minutes and 20 seconds, then turn off when the clock runs out. But, depending on the size of the bag you're popping (the usual bad contains about 3.5 oz of kernels and oil, but some are smaller), you might end up scorching the popcorn long before that time has counted down. So, even with a popcorn button, it's important to use the listening method of stopping the cooking process when you hear 2 to 4 seconds between single pops.

However, on some microwaves, the magnetron is connected to an inverter that effectively reduces the amount of microwave radiation it produces, thereby keeping the magnetron on at all times, but simply reducing how potent its output is according to the user-selected power setting. On these models (such as Panasonic microwaves that note on their doors that they have an inverter), the popcorn button serves two functions. First and foremost, it does what all popcorn buttons do--it sets a pre-programmed cooking time. But, more importantly, it also automatically reduces the magnetron's power output during the cooking process to reduce if not completely eliminate scorching. These microwaves are generally so powerful at full output that you actually want to use the popcorn button, even if the instructions on the popcorn bag say not to, because using them at full power for the entire cooking time can scorch popcorn that's already popped while the other kernels are still popping like crazy.

Finally, on some models of both types of microwaves, the button might have additional settings for the specific size of the bag you're popping, whether 3.5 oz, 2 oz, etc.