Winemaking in combination with phosphorus and potassium, nitrogen can serve as a critical factor in yeast growth and therefore fermentation, notably in home winemaking of fruit wines. Ammonium ions, primary amino acids, and small peptides, but not the secondary amino acids proline and hydroxyproline, are the principal forms of nitrogen present in grapes that can be used by yeast; these nitrogen components constitute what is often referred to as yeast assimilable nitrogen (YAN). Simple tests have only recently been developed for measuring YAN so that a deficiency of this essential yeast nutrient can now be easily determined. When a deficiency occurs, an ammonium salt, usually diammonium phosphate (dap), is often added. Nitrogen can also affect wine composition: in high concentrations it is associated with intensified aromas, while low concentrations favour the formation of hydrogen sulfide.
