Reagentless amperometric biosensors for glucose and ethanol were developed and successfully applied for monitoring glucose and ethanol concentrations in wine during the fermentation process. The glucose biosensor was based on commercially available glucose oxidase and horseradish peroxidase co-immobilized on solid graphite using Os(II)-redox hydrogel (RH) [1]. In the case of ethanol biosensor, the quinohemoprotein dependent alcohol dehydrogenase was immobilized on the graphite electrode surface using the same RH [2]. Both biosensors were operated at low applied potentials (-50 mV vs. Ag/AgCl, KCl _{0.1 M} for glucose biosensor, and 250 mV vs. Ag/AgCl, KCl _{0.1 M} for ethanol biosensor), where biases from interferences are minimal. The bioelectroanalytical parameters, estimated from flow injection analysis measurements, were found as follows: sensitivity, 0.73 ± 0.01 μA mM^-1 for glucose and 0.45 ± 0.01 μA mM^-1 for ethanol; linear range up to 1 mM in both cases; detection limit, 7.0 μM for glucose and 8.9 μM for ethanol. The results for real samples were found in good agreement with those reported by Barsan et al. [3].