Can you superheat coffee? As far as I know, heating clean water can lead to superheating to over 100 degrees but how clean does it have to be?
Coffee is almost all water but is it clean enough to lead to superheating? What about instant noodles? How pure does the water have to be? Can it explode in a microwave?
 A: First, to be clear, the term 'superheating' in general parlance might be a little different from its use in thermodynamics. In general parlance, 'superheating' might be used for the sort of thing you can get in a pressure cooker or a high-pressure steam engine, where the boiling point is higher than 100$^\circ$C because the pressure is higher. But 'superheating' as a term applied to phase transitions in thermodynamics refers to the special behaviour in first order phase transitions where the phase which is stable at lower temperature persists even when the temperature is above the transition temperature. This is what I understand the question to be about.
A 'superheated' body of water in this sense could be, for example, pure water at one atmosphere of pressure and $110^\circ$C. At this temperature the water will eventually turn to steam but it can take a surprisingly long time to happen if there are no irregularities on the walls of the container and no little bits of dust or undissolved molecules suspended in the water. Such bits can act as nucleation centres which enable bubbles to grow by getting them past a potential hill at low radius of curvature owing to surface tension.
For coffee, such superheating will not occur if there are coffee grounds suspended in the liquid, because they will act as nucleation centres. But if the coffee is carefully filtered so that you are left only with a liquid with everything fully dissolved and nothing suspended, in that case I expect superheating can occur. I say 'I expect' not 'I know' because I have no direct experimental evidence to draw on and I have not read of anyone trying it. I am writing just from general knowledge of thermodynamics. This general knowledge assures me that a liquid does not need to be chemically 'pure' (i.e. just one species of molecule) in order to show the properties of liquids in a phase transition. But it does need to be 'pure' in the sense of having no nucleation centres in order to get superheating.
A: All of the different ink compositions used in HP's thermal inkjet printheads over the last 38 years do experience very large amounts of superheat- and none of them are pure water. They are very complicated mixtures of solvents, colorants, humectants, surfactants, biocides, resins, and water- and all of them must be able to sustain superheating, otherwise they could not be used in thermal inkjet printheads.
During my time in that industry I surreptitiously superheated and thereby jetted pinot noir and bourbon out of examples of our printhead designs and I have no doubt that carefully filtered coffee could be jetted as well. (I also routinely created superheat vapor explosions in cups of tap water placed in a microwave oven, with truly spectacular results.)
Those printheads routinely superheated their inks (with normal boiling points of ~100C) to temperatures between 260C and 280C, by heating those inks at a rate of more than 100C per microsecond.
