Wort FAN—Its characteristics and importance during fermentation

GRAHAM G. STEWART (1), Christoforos Lekkas (1), Anne E. Hill (1)
(1) International Centre for Brewing and Distilling, Heriot-Watt University, Edinburgh, U.K.

FAN (free amino nitrogen) is the sum of the individual wort amino acids, ammonia, and small peptides (mainly di- and tripeptides). FAN is an important general measure of yeast nutrients which constitute yeast-assimilable nitrogen during wort fermentation. Even if attenuation of wort carbohydrates proceeds normally, the same quality of beer is not always guaranteed to be produced, suggesting that the sugar content of wort alone is not a good indicator of yeast fermentation performance. The wort’s nitrogen content is used by the yeast in order to accomplish its metabolic activities which include the synthesis of de novo amino acids leading to the synthesis of structural and enzymatic proteins. FAN has been regarded as a better index for the prediction of healthy yeast growth, viability, vitality, fermentation efficiency. and consequently beer quality and stability. Studies have identified “marker” amino acids and other wort nitrogen constituents that are responsible for stimulating and reinforcing fermentative activity. In addition, synergetic effects between wort free amino acids, small peptides. and ammonia in terms of improved yeast fermentation efficiency have been examined.

Graham Stewart is the Emeritus Professor of Brewing and Distilling at Heriot-Watt University, Edinburgh, Scotland, and Special Professor in Bioethanol Fermentation at Nottingham University, England. He was the director and professor of the International Centre for Brewing and Distilling, Heriot-Watt University, from 1994 to 2007. From 1969 to 1994 he held a number of technical positions with Labatt’s in Canada and from 1986 to 1994 was its brewing technical director. He was the president of the Institute of Brewing (now the Institute of Brewing and Distilling) in 1999 and 2000. He is also a member of ASBC and MBAA. He holds fellowships in the IBD, the Institute of Biology, and the American Academy of Microbiology. He has more than 250 publications (books, patents, review papers, articles, and peer-reviewed papers) to his name. Since his retirement he has established a consulting company—GGStewart Associates—and has an office in Cardiff, Wales. As well as being awarded the IBD Horace Brown Medal (2009), he has also been presented with the ASBC Award of Distinction (2008), the MBAA Presidential Award (1983 and 1998), the MBAA Award of Merit (2009), and the Society of Industrial Microbiology Charles Thom Award (1988).