You should be able to change the emissivity on the unit. A perfect mirror polish on stainless will be something like 0.1 (0 being no heat is radiated ) but in reality after being roughed up they will probably be in the 0.5-0.8 range. 1 is a perfect black body, ie transmits heat perfectly, like a black fireplace.
Meanwhile, you should be able to see through the keg. Can you adjust the range of temps on it to get a clearer line between liquid and gas?
You could also use it for kettles to see temp on the bottom if your cold welded fittings are at risk, and compare surface heat with different insulation types - after adjusting for emissivity of course.