Yeast: Difference between revisions

The minimal wort FAN level to achieve satisfactory yeast growth and fermentation performance in normal gravity wort fermentations (12°P) is 130 mg/L but, for rapid attenuation resulting in higher ethanol production, increased levels of wort FAN are required (170–190 mg/L). Meilgaard suggested that, during normal wort gravity fermentations, a minimum FAN level of 150 mg/L is required to permit rapid and complete attenuation. However, optimal wort FAN levels differ from fermentation to fermentation and from yeast strain to yeast strain; thus, they are considered controversial and unverified and are just guidelines. Furthermore, the optimum FAN values change with different wort sugar levels.<ref name=lekkas>Lekkas C, Hill AE, Stewart GG. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-2014-0113-01 Extraction of FAN from malting barley during malting and mashing.] ''J Am Soc Brew Chem.'' 2014;72(1):6–11.</ref> Wort FAN  is affected by the malt/adjunct ratio, the mashing schedule, barley variety, barley growth conditions, and various malting parameters. Under high-gravity brewing conditions, brewing yeast strains need extra FAN to cope with increased osmotic stress, other stress conditions, and the additional yeast growth required for efficient wort fermentation. This means that, as wort gravity increases, the levels of assimilable nitrogen should also increase in order that a certain rate of glycolytic flux and high cell viability and vitality is maintained. This avoids incomplete fermentations. Finally, FAN is used to provide not only nitrogen to the yeast cells for growth but also the wort nitrogen content or its metabolic products which affect beer flavor compounds and overall stability.