I tried preparing a supersaturated solution of caffeine by mixing anhydrous caffeine powder with water in a thin Turkish tea glass and heating it up over a candle (desperate times...).
This worked as expected and a lot more caffeine dissolved into the clear solution after I slowly swung it back and forth over the flame. The water didn't boil, no visible vapors formed on the surface, and I was holding the glass with my fingers, so I would say that the temperature was well below 100°C.
After the solution cooled down, instead of crystals precipitating, I found the glass filled with a fibrous cotton-like white mass. I pulled it out (it mostly stuck together) and dried it up on sheets of paper. Now I have white flakes which are flexible instead of brittle (still feel very much like cotton).
This would seem an awful lot like some polymer forming - except the substance tastes a lot like crystalline caffeine, and melts and evaporates much like caffeine - with the vapors having the same distinctive acrid (but not burnt) smell.
I'm pretty sure the answer to the polymer question is no, but in case I'm right I'd be very curious as to what's actually happening.
