What factors influence higher-alcohol production during fermentation?
A.Yeast strain: The amounts of higher alcohols produced by different strains can vary by as much as fivefold.
B.Fermentation temperature: Generally, higher fermentation temperatures produce greater levels of higher alcohols(particularly phenyl ethanol ). Some yeast stains are more sensitive to this effect than others. Some brewers utilize top pressure during primary fermentation if conducting a rapid,warm fermentation to minimize this affect.
C.Pitch rate:With high pitch rates, there is less yeast growth and, therefore, less higher-alcohol production. Underpitching can lead to excess levels.
D.Wort gravity: Higher-gravity worts yield increased levels of higher alcohols.
E.Wort aeration: Increased aeration rates or aeration after the start of fermentation leads to increased production of higher alcohols.
F.Wort composition: Low FAN levels, particularly in high adjunct beers,can lead to increased higher-alcohol production. Excessive levels of wort FAN or zinc can also increase higher-alcohol production.
G.Fermenter type:Tall,slender vessels promote production of higher alcohols.