Sometimes it's more convent to me the leave some chocolate totally untempered and temper it when needed. When I try to melt it there are many clumps that doesn't melt no matter what I do and those clumps have really bad effect on the final product, i.e. far from smooth-very gritty although from the outside it looks fine (in contrast to temper chocolate from the same batch which tempered right after conching).
An important factor is that the regular temperature is usually 28C so it takes days to harden when untempered.
What is the reason for this? It means that under-tempered chocolate cannot be smooth again?