Beer or wort FAN analysis provides free amino nitrogen content (mg/L FAN) of the sample. Each amino acid, dipeptide, polypeptide, and protein unit has a single free amino group that stain a dark blue color in the presence of ninhydrin. Because the analysis is biased toward smaller molecules, wort and beer FAN is highly correlated to total amino acid concentration.
Free amino nitrogen (FAN) is an important general measure of amino acids, ammonium ions, and small peptides which constitute the nitrogen that yeast can assimilate during brewery fermentation. This analysis can be done at various stages of fermentation from wort to final beer to evaluate utilization. While FAN levels below about 100 mg/L can cause fermentation problems, high FAN levels, particularly in finished beer, decrease microbiological stability of unpasteurized/non-sterile filtered beers and increase the susceptibility to oxidative reactions that contribute to staling aldehydes.