I often "touch test" microwaved food to see if it is heated up enough to my preference. In doing so, I sometimes notice the characteristic tingle of a static discharge between the food and my finger (pretty sure I've at least once or twice seen a tiny spark). This comes as a bit of a surprise because I would not have expected there to be any way a static potential could have accumulated between myself and the contents of a plate in the oven from the time I put it in to the time I open the door and "touch test". I notice this often with foods that have a moderate amount of moisture - a piece of meat, cooked vegetables, mashed potatoes, etc.
This leads me to wonder whether the action of the microwaves could somehow induce a static charge - large enough to notice as either visible spark or at least feel - and that could linger after the oven shuts off for the amount of time it takes to open the door, reach in, and touch it. I don't believe I've picked up and retained a charge on my person - I've just opened the oven's door - I should be at the same electrostatic potential as the oven itself.
My understanding of electronics and physics tells me that microwaves are an alternating electromagnetic field - not something that could produce a static charge without at least something to act as a rectifier. I can't imagine that such a mechanism could "just happen" to exist in food on a plate.
Could microwave energy continue to resonate within the oven even after power has shut off? If so, could this explain the small but noticeable discharge? I would expect any such resonances to decay to practically nothing almost instantaneously, but could this be wrong?
Since the microwave oven in question has a turntable, is the explanation unrelated and more mundane: triboelectricity from the action of the turntable?