A process for the production of a refined dianhydrosugar-containing product is disclosed. The process includes controlled continuous crystallization of the dianhydrosugar-containing product to produce a solution saturated with the dianhydrosugar. The saturated solution is mechanically separated, for example by centrifugation, and the crystalline product is washed. The only solvent used is water. The dianhydrosugar-containing product is upgraded to at least 99.8% purity and recovery is 95% or greater.Recrystallization of the dianhydrosugar of 99.8% purity results in an ultra pure product containing at least 99.99% dianhydrosugar.