Dextran-producing strains of Leuconostoc mesenteroides ssp. cremoris, i.e. those registered at the CNCM under the designations l-1692 and l-1693, are new. Also claimed are: (a) production of dextran by fermenting a culture medium containing sucrose by inoculation with a preculture of a selected strain of Leuconostoc mesenteroides ssp. cremoris; and (b) recovering an additive containing the enzyme dextran-sucrase from the fermentation product.