In brewing, Free Amino Nitrogen (FAN) is a measure of the concentration of individual wort amino acids and small peptides (one to three units) which can be utilised by yeast for cell growth and proliferation. For vigorous fermenation, a sufficient quantity of FAN must be present in the wort. An excessive concentration in the wort is not desirable however, as this may cause production of a significant quantity of fusel alcohols, or spoilation of the finished beer by other organisms.

References

• Research Newsletter of the International Centre for Brewing and Distilling, Winter 2003.
• Making Sense of FAN, Moritz Kallmeyer.