Nitrogen compounds in the wine grape must

The total nitrogen content of wine grapes as well as the relative distribution of nitrogen compounds influences the production of yeast biomass and fermentation rate. It can also affect the different types of alcohol present, as a result of yeast metabolism, in the resultant wine. Free amino nitrogen (FAN) is often used as a measure of the suitability of nitrogen types available for yeast growth and fermentation. 

Arginine, one of the amino acids present in high concentrations, can be used as an indicator of the nitrogen richness or quality of the must. On the other hand, levels of proline, another amino acid present at high levels in the must, bare little relation to the total nitrogen content.

For complete, good quality fermentation, a must containing a minimum of 140 mg assimilable N/l is required. Without these levels of nitrogen in the must, there is a reduced capacity to produce alcohol resulting in a sluggish or stuck fermentation. 

Total nitrogen content, as well as arginine concentration, is directly influenced by application timing of nitrogen fertilizers to the vine. As with potassium, the correct balance of nitrogen for vine growth and grape development is important.

Nitrogen 

Nitrogen fertilization can positively influence aroma, flavour and wine quality scores (Figure 25). The right form of nitrogen is particularly important in this; trials show that free amino acid nitrogen can also increase wine aroma.

High rates of nitrogen also increase the nitrogen content in the grape juice.