Under wine-making conditions, alcoholic fermentations are carried out without on-line monitoring due to the lack of robust, precise and cheap sensors.Wedescribe the interest of on-line monitoring electrical conductivity and his good correlation with pH during fermentation. The change in conductivity is primarily due to the assimilation of nitrogen (in particular, ammoniacal nitrogen), which is usually the limiting nutrient of the fermentation kinetics. The limits of conductivity measurement to follow the nitrogen assimilation were discussed with the variability observed with five different grape musts.