Breweries use different yeast strains to create beers with different flavours and aromas. Yeast propagation must produce yeast that performs consistently from the first fermentation to harvesting and re‐pitching in subsequent fermentations. Breweries propagate yeast in wort leading to low efficiency fermentative growth in Crabtree‐positive yeast. There is limited knowledge on the impact on beer production when fermenting with yeast propagated in sugar limited and nutrient supplemented wort. It was hypothesised that propagating yeast in this way would have a positive impact on subsequent fermentation performance. Saccharomyces cerevisiae was propagated at the laboratory scale in standard wort with a high carbon to nitrogen (C:N) ratio (850) or in modified wort supplemented with yeast extract to achieve a low C:N ratio (100) and at varying sugar concentrations. Propagation in low C:N wort with 2°P sugar yielded a 27% decrease in fermentation efficiency and a 46% increase in cell production compared to 2°P high C:N wort. This suggests nitrogen is critical to the respiro‐fermentative balance during growth. Yeast propagated in standard wort resulted in slower fermentations and significant under‐attenuation compared to yeast grown in the modified wort with low sugar and high nitrogen. The results of this study suggest the nitrogen and sugar content drive the respiro‐fermentative balance during yeast propagation. The metabolism of yeast during propagation induces significant downstream impacts on the subsequent fermentation performance and wort attenuation. © 2020 The Institute of Brewing & Distilling

中文翻译：

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酵母繁殖过程中呼吸发酵平衡对发酵和麦芽汁减毒的影响

啤酒厂使用不同的酵母菌株来生产具有不同风味和香气的啤酒。酵母菌的繁殖必须产生从第一次发酵到收获和随后的再发酵都始终如一的酵母。啤酒厂在麦芽汁中繁殖酵母，导致Crabtree阳性酵母的发酵效率低下。当用在糖有限和营养补充麦芽汁中繁殖的酵母发酵时，对啤酒生产的影响的知识知之甚少。假设以这种方式繁殖酵母将对随后的发酵性能产生积极影响。酿酒酵母在实验室规模下，以高碳氮比（C：N）的标准麦芽汁（850）或补充酵母提取物的改良麦芽汁以低C：N比率（100）和不同的糖浓度进行繁殖。与2°P高C：N麦芽汁相比，在低C：N麦芽汁中以2°P糖繁殖时，发酵效率降低27％，细胞产量提高46％。这表明氮对于生长期间的呼吸发酵平衡至关重要。与在低糖和高氮的改良麦芽汁中生长的酵母相比，在标准麦芽汁中繁殖的酵母导致发酵较慢，并且衰减明显不足。这项研究的结果表明，氮和糖的含量在酵母繁殖过程中驱动呼吸发酵平衡。繁殖过程中酵母的代谢对后续的发酵性能和麦芽汁衰减产生重大的下游影响。©2020酿酒与蒸馏研究所