Daniel GRANES, Edouard MEDINA, Lucile BLATEYRON, Céline ROMERO, Eric BRU, Christophe ROUX, Caroline BONNEFOND, Agnès PIPERNO, Myriam ROUANET, Thomas O

In the living world, nitrogen is an essential element which is present in the composition of amino acids, peptides and proteins. For yeasts in particular, these proteins are constitutive elements of the cell and of its organelles (structural proteins) or of enzymes which intervene as transporters or in metabolic reactions (functional proteins). Nitrogen is therefore a key factor for the multiplication and physiological activity of the yeasts. When one talks about nitrogen, all the molecules which consist of one or more nitrogen atoms are encompassed. However, not all the nitrogen can be used by the yeasts: P. Barre, V. Jiranek and others therefore defined assimilable nitrogen as the quantity of nitrogen in mg/L which is at the time available and susceptible to be used by the yeasts. When we will speak further of nitrogen, it will always be in reference to this definition, unless otherwise indicated. The assimilable nitrogen consists of amino nitrogen and amino acids. Among all the amino acids, certain ones such as proline are not assimilable by the yeasts. The measurement of the assimilable nitrogen takes into account only the assimilable amino acids. On a synthetic medium and in pure culture, the complete fermentation of 200g/L of sugar (around a potential of 12°) can only be completed when initial levels of assimilable nitrogen are higher than 150mg/L, due to this fact, this is defined as the level of “absolute deficiency”. The assimilable nitrogen can represent less than 50% of the total nitrogen. The quantity of nitrogen assimilated by the yeasts has four important impacts and these in part depend on one another. The supplies during the multiplication phase and stationary phase are the most efficient. It is therefore always of preference to act preventatively. Attention however to negatively interpreting a supply said to be “initial”. For the classic supply at the end of the growth phase, the addition combined with O2 must be standardized for reds as for with white or rosés.
Published on 28/08/2008
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