To improve the storability of sugar beets, the study aimed at determining reasons for genotypic variability in sugar losses and invert sugar accumulation during storage, and at identifying indirect criteria to select for varieties with low storage losses prior to storage. In 2011 and 2012, 18 genotypes, and in 2012 and 2013, 6 genotypes cultivated at two locations were stored for 8 and 12 weeks at 8 °C under controlled conditions. The same 18 genotypes were grown under stress conditions in Spain in 2012/13. Sugar losses were closely correlated to the invert sugar accumulation after storage. Genotypic differences in storage losses were primarily caused by differences in the level of infestation with microorganisms. The invert sugar accumulation was lower for genotypes with high marc concentration before storage, pointing to a non-specific resistance. Additionally, the sugar concentration in dry matter before storage, and the invert sugar concentration after cultivation under stress conditions correlated with the invert sugar concentration after storage. These parameters are therefore suggested as criteria to select for improved storability of sugar beet genotypes.