Assimilable nitrogen addition and hexose transport system activity during enological fermentation

Addition of ammoniacal nitrogen to nitrogen-limited musts is widely used by enologists to reduce the time required for the completion of fermentation. Nevertheless the physiological basis of the actual effect of such an addition is not fully understood. The effect of ammoniacal addition was studied on a nitrogen-limited must under conditions whereby addition had no effect on yeast growth. In these conditions nitrogen addition promotes increase of protein synthesis rate and activity of the hexose transport system. The results suggest that the reactivation of the hexose transport system does not require a de novo biosynthesis of sugar carriers, but the synthesis of an unknown regulatory protein.