Roasting green beans in a popcorn popper
You can pickup a popcorn machine from any store which sells small electrical goods. You need to ensure the popper uses hot air to pop the corn kernels.
Generally the poppers take approx 80grams of green beans and roast from anywhere from 6-10mins depending on the power of machine and outside temperature.
You will want to put in the green beans and manually agitate them with a wooden spoon until they dry out somewhat, making them light (weight) enough to move around themselves. Manual agitation also removes chaff and avoids burning. You should be able to leave the beans to manually move around by themselves from then on checking them often until they are roasted to your liking.
will try it, it seems interesting though.