The β-glucosidase preparation from the cultivation liquid of Aspergillus niger 33/20/K was applied for the reduction of viscosity and improvement of fermentation conditions of rye mashes, average density 17.4 ⁰ Blg, as obtained by the pressureless method. Mashing, fermentation and distillation were carried out on agricultural - distillery scale using liquefying enzyme Termamyl, saccharifying enzyme SAN Super 240 Land dry distillery yeast race As-4. β-Glucosidase ~ 5 AU/L was added to mashes at 40⁰C before the yeast addition. Fermentation was carried out for 72 h. Mash viscosity, the contents of high molecular weight β-glucans and arabinoxylans, ethanol yield and fermentation by-products were determined. β-Glucosidase preparation was found to reduce rapidly the mash viscosity during the first 24 h of fermentation and decrease considerably the contents of β-glucans and arabinoxylans. The addition of β-glucosidase preparation did not cause the deterioration of high vines, in some cases, even improving them.