A stressful fermentation results in aroma defects and production of factors inhibiting bacteria.

Yeast must have complete nutrition for a stress-free fermentation. Grape nutrition additions need to be balanced in both growth and survival factors for the yeast to ensure a clean and strong fermentation finish.

The nitrogen sources that can be used by Saccharomyces cerevisiae are ammonium (NH4 +) and amino acids (organic nitrogen). They both represent assimilable nitrogen and are present in must at varying concentrations, sometimes not in sufficient quantities to meet the requirements of the yeast. The three following factors must be taken into consideration:
 

1. Below 150 mg N/L, must is deficient. It is therefore important to supplement it with nitrogen elements.

2. Yeast nitrogen requirements depend on sugar concentration. The higher this concentration, the greater the amount of yeast biomass needed to successfully achieve a thorough breakdown of the sugars during alcoholic fermentation. Although, the yeast biomass must not be too excessive to avoid an induced nitrogen deficiency.

3. The nitrogen initially present in must is rapidly assimilated during the first third of the alcoholic fermentation (d-30), at the point when the biomass is at its highest density. Consequently, irrespective of the initial nitrogen content, its addition during alcoholic fermentation (d-30) allows to preserve the biomass formed, which is dependent on the yeast strain and proportional to the initial nitrogen concentration.