Abstract

Flocculation of yeast is a natural phenomenon wherein cells clump together and come out of suspension. This is often relied upon by brewers as a natural means of removing yeast, as clumps of yeast cells (flocs) typically precipitate from the fermentation vessel. A problem that has long frustrated brewers is when yeast flocculation does not proceed as expected. This has been linked to a fermentation’s premature ending (“hung” fermentation). Since the early 1900s, researchers have explored numerous methods to identify the flocculation characteristics of yeast. Traditional methods have contributed to an understanding of the fundamentals of flocculation by assessing the impact of stressors (e.g., pH, temperature, wort density and composition, and ethanol content) on the flocculence of yeast. In 1994, conventional measurement techniques were combined with modern technology to develop the American Society of Brewing Chemist’s method “Yeast 11,” which was revised by the society in 2011. This method succeeded in the identification and definition of the flocculence characteristics of particular yeast strains but has not taken into account the changes in flocculation tendency over time for later generations of the same yeast strain. The ASBC also describes a fermentation assay to assess aberrant yeast behavior such as premature yeast flocculation (PYF) in the “Yeast 14” method. The current challenge in flocculation research is understanding the changing genetics of flocculation throughout the usage of a yeast strain in a fermentation process. This review details the evolution of yeast flocculation measurement, our current understanding, and potential future developments.

摘要

酵母的絮凝是一种自然现象，其中细胞聚集在一起并脱离悬浮液。酿酒商通常将其作为去除酵母的天然方法，因为酵母细胞团块（絮状物）通常会从发酵容器中沉淀出来。长期困扰酿酒商的一个问题是酵母絮凝没有按预期进行。这与发酵过早结束（“挂起”发酵）有关。自 1900 年代初以来，研究人员已经探索了多种方法来识别酵母的絮凝特性。传统方法通过评估压力因素（例如，pH、温度、麦芽汁密度和成分以及乙醇含量）对酵母絮凝的影响，有助于了解絮凝的基本原理。1994 年，将传统的测量技术与现代技术相结合，制定了美国酿酒化学家协会的方法“酵母11”，该方法于2011年由该协会修订。该方法成功地识别和定义了特定酵母菌株的絮凝特性，但尚未考虑到同一酵母菌株后代的絮凝趋势随时间的变化。ASBC 还描述了一种发酵测定，用于评估异常酵母行为，例如“酵母 14”方法中的酵母过早絮凝 (PYF)。当前絮凝研究的挑战是了解在发酵过程中酵母菌株的整个使用过程中絮凝遗传的变化。这篇综述详细介绍了酵母絮凝测量的演变，我们目前的理解，