Yeast: Difference between revisions

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*https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5003802/

The ventilation of wort before fermentation is a necessary step to ensure the full growth and better fermentation of yeast (Depraetere, De Schutter, Williams, & Delvaux, 2008). With further increase of dissolved oxygen in wort, the content of SO2 decreases obviously, which indicates that too much dissolved oxygen in wort inhibits the production of SO2 (Dufour, 1991). That is, controlling dissolved oxygen can improve generation of SO2 and antioxidative activity of beer. The pitching rate of yeast was found to be able to control the fermentation time and the peak number of yeast cells and also had an effect on the composition and flavors of beer (Verbelen, Saerens, Thevelein, & Delvaux, 2009). Low pitching rate affects the multiplication of yeast during the main fermentation stage, results in a smaller reduction in apparent extract and retards fermen tation. In contrast, higher pitching rate leads to vigorous growth of yeast and rapid decline of apparent extract during the main fermentation stage. An increase in pitching rate leads to a decrease in the quantity of SO2 produced by fermentation. This may be explained in that when the pitching rate is high, the yeast metabolism is exuberant, so that more sulfites are metabolized by the yeast to synthesize the amino acids needed for its own metabolism, resulting in less SO2 (Zhou, 2010). Therefore, the appropriate pitching rate is crucial for generating SO2 during beer fermentation (Zhao, 2012).<ref name=yangao>Yang D, Gao X. [https://www.sciencedirect.com/science/article/abs/pii/S0924224421001552 Research progress on the antioxidant biological activity of beer and strategy for applications.] ''Trends Food Sci Technol.'' 2021;110:754-764.</ref>

==Preparing yeast for fermentation==