THE DEMAND FOR YEAST NITROGEN
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:
• Below 150 mg N/L, must is deficient. It is therefore important to supplement it with nitrogen elements.
• 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.
• 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.
WHY ORGANIC NUTRITION ?
Organic nitrogen is supplied by adding yeast derivatives (usually autolysed yeast). In addition to amino acids, these yeast derivatives include lipids, vitamins and minerals which also contribute to the efficient performance of the yeast. Yeast has the ability to simultaneously assimilate organic nitrogen and mineral nitrogen from the beginning of the alcoholic fermentation. Organic nitrogen must be present in order to:
• Limit the production of SO2 and sulphur compounds (H2S and mercaptans).
• Produce healthy, but not excessive, biomass.
• Limit the risk of stuck or sluggish fermentation.
ORGANOLEPTIC EFFECTS OF ORGANIC NUTRITION
Numerous experiments show that improved outcomes of alcoholic fermentation can be achieved with the use of organic nitrogen. Even in the case of wines considered dry (glucose + fructose < 2 g/L), small amounts of fermentable sugars can be used by degrading microorganisms and can have an adverse effect on the quality of the wines (Figure 2). Besides its effects on fermentation kinetics, the addition of oragnic nitrogen can increase the fruitiness of wines and limit the aromatic mask linked to the production of sulphur compounds during the alcoholic fermentation. Except for the source of the nitrogen added, a comparison of wines produced under the same conditions reveals significant preferences for wines derived from musts supplemented with NUTRISTART® ORG (table 1). The wines are considered fruitier, fresher, less vegetal and subject to less reduction than those supplemented with mineral nitrogen alone.
In addition, don’t hesitate to use our DMT - yeast nutrition: nitrogen adjustment - to define a custom protocol, adapted to the needs of your must
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