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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.

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Google Images "caffeine crystals" They are beautiful fibrous masses. The solvent can influence crystal shape by making various faces grow faster or slower. Benzil slowly crystallized from hot optically resolved pinene is slender needles. Crystallized from room temp supersaturated mixed xylenes with a needle seed crystal, it is single crystal blocks.

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    $\begingroup$ so why would the crystals be flexible? also, why would they not adhere at all to the glass, and not precipitate, but rather form as clouds in the solution? $\endgroup$
    – TheChymera
    Feb 21 '14 at 15:06
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    $\begingroup$ The crystals are flexible given aspect ratio. 1 cm of thin spaghetti is rigid. 30 cm easily flexes. Dust in the water affords multiple nucleation centers. Bottled water is free of particles. Wrap the hot liquid in a rag for much slower cooling. Try recrystallizing caffeine from vodka, lxsrv7.oru.edu/~alang/onsc/solubility/… (alcohol vapors are flammable). $\endgroup$
    – Uncle Al
    Feb 21 '14 at 21:26

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