they’ll do what you tell them to. not quite the right tool, but for off the shelf R&D they come reasonably close.
getting a dishwasher turbidity sensor in the mix to
would be the next trick…so you don’t have to sit there with a flashlight twiddling knobs.
although I now wanna go at that with a laser pointer 
shine laser through jar. when red dot gets to a certain size, turn the heat on. when it reduces again, turn it off. have an Arduino make those decisions based on a pair of appropriately spaced photosensors (maybe a fraction finder would work).
just wish this coffee cup warmer was rated for butane 