Why does chocolate go grainy when I melt it? I was melting chocolate and it turned into a thick, grainy mess. What happened and what can I do about it? I followed this common method to melt chocolate:
I used a double boiler i.e. I put a heat proof or glass bowl in the mouth of the pot having water, making sure the water doesn't touch the bottom of the bowl. Stirring chocolate occasionally as it softens.
When your chocolate goes grainy it's called "seizing". There are two main reasons for it to seize:


Water: water getting into the bowl of the double boiler, either because it wasn't dry in the first place, or because of condensation.
Overheating (burning).


Unfortunately, once chocolate has seized there aren't reliable ways to re-temper that particular batch.  Use it for baking or turn it into chocolate sauce, or something.