Caramel - changed sugars, now it gets grainy quickly

I used to use white sugar and sorghum syrup, now I use organic cane with sorghum syrup and brown rice syrup.

The pieces are stable for a couple of days, then begin to crystalize.

Suggestions? Is it balancing fructose / sucrose?

updated by @alan-crofut: 04/17/15 12:18:54AM

I can't speak to the mixture of sorghum and brown rice, but cane sugar tends to have larger granules the processed white sugar. make sure when cook your caramel as low and slow as possible and wipe down the edges of the pot often with a wet pastry brush. I switched to cane sugar last year and had a few batches turn out pretty badly. Stirring thoroughly at the beginning and the wet pastry brush (more often than with white sugar) really seemed to help.
Andrea