\u00b7 Adding nitrogen to vine plants increases the nitrogen concentration in the . rail Many components of the rail which contribute to the taste and aroma of the wine are affected by the addition of nitrogen directly or indirectly. Thus, changes in the concentration and composition of nitrogen compounds in the must can positively or negatively affect the composition of the wine produced. Many of these effects are modified through the metabolism of yeasts during fermentation.<\/p>\n\n\n\n
\u00b7 In order to understand how the type of nitrogen compounds and their concentration in the rail affects the growth and metabolism of , yeasts and the conversion of the grape-derived flavour and aroma precursors , it is necessary to know which nitrogenous components of the rail are important. Whilst the must is relatively rich in nutrients necessary for , yeasts, the nitrogen content was found to exhibit a pronounced , variation not so much in concentration but in the type of nitrogen compounds present. Only some of the main nitrogen compounds in the rail are important for yeasts.<\/p>\n\n\n\n
\nWhilst the must is relatively rich in nutrients necessary for , yeasts, the nitrogen content was found to exhibit a pronounced , variation not so much in concentration but in the type of nitrogen compounds present. Only some of the main nitrogen compounds in the rail are important for yeasts.<\/p>\n<\/blockquote>\n\n\n\n
* The basic yeast used in , fermentations Saccharomyces cerevisiae , preferably uses simple sources of nitrogen such as ammonium ions and nitrogen compounds with a free amino group , found in the form of primary amino acids<\/p>\n\n\n\n
\u00b7 Secondary , amino acids such as proline and hydroxyproline are not significantly metabolised under normal winemaking conditions.<\/p>\n\n\n\n
Low molecular weight peptides can also be used.<\/p>\n\n\n\n
Grape proteins, on the other hand, cannot be used as a source of nitrogen as Saccharomyces cerevisiae lacks significant extracellular proteolytic activity.<\/p>\n\n\n\n
So the fraction of nitrogen that can be used is often referred to as assimilable nitrogen (Yeast Assimable Nitrigen).<\/p>\n\n\n\n
* The remaining components of total , nitrogen including proline and hydroxyproline ,, high molecular weight peptides and proteins are referred to as non-assimilable nitrogen from yeasts (Yeast Non Assimilable Nitrogen). * Depending on the , analytical method used, nitrates are included in the non-digestible nitrogen , as Saccharomyces cerevisiae lacks the ability to digest nitrates.<\/p>\n\n\n\n
\u00b7 Analytical determination of the nitrogen assimilable by yeasts is now a crucial measurement for the management of , fermentation as the determination of nitrogen by analysis of plant tissues does not ensure reliable prediction of the nitrogen assimilable by yeasts at harvest.<\/p>\n\n\n\n
The content of the assimilable nitrogen from the yeasts in the rail is the key factor that will determine the composition and concentration of the assimilable nitrogen components of the must.<\/p>\n\n\n\n
Losses of assimilable nitrogen due to harvesting and transport conditions should be taken into account.<\/p>\n\n\n\n
\u00b7 Factors such as the choice of treatment methods (effect on the extraction of assimilable nitrogen) ,, the management of the existing yeast population and the addition of additional assimilable nitrogen to the winery have their role in determining the final composition and concentration of assimilable nitrogen in the must. <\/p>\n\n\n\n
Source: Bell S-J and P.A. Henschke , 2005. <\/strong>Implications of nitrogen nutrition for grapes , fermentation and wine. Australian Journal of Grape and Wine Research 11 , 242-295.<\/p>\n