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).
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