Alkyl glycosides can be synthesized by glycosidases in organic media with limited amounts of water. These systems, however, limit the solubility of the sugar substrates and decrease reaction yields. Herein we report the enzymatic synthesis of heptyl-beta-glycosides in heptanol catalyzed by a hyperthermophilic beta-glycosidase at 90 degrees C. Our results indicate that dispersion of water in heptanol changes with time producing coalescence of water at the bottom of the reactor, playing a key role in the reaction yield. Water-soluble substrate, enzyme and products are concentrated in the aqueous phase, according to their partition coefficients, promoting side reactions that inactivate the enzyme. Reaction yield of heptyl-beta-glycosides was 35% relative to lactose, at 7% water. The increase in the water phase to 12% diminished the enzyme inactivation and increased the heptyl-beta-glycosides yield to 52%. Surface-active compounds, SDS and octyl glucoside, increased water dispersion but were unable to prevent coalescence. (C) 2013 Elsevier Ltd. All rights reserved.