Effect of the respiro-fermentative balance during yeast propagation on fermentation and wort attenuation

Effects of regional location on the genotype and phenotype of historical Irish brewing yeast

Most commercial beers are made using water, malted barley, and hops as the principal ingredients and Saccharomyces yeast as the transforming microorganism. The yeast is used in a semi-conservative process in which crops are collected from one fermentation, stored, and a proportion recycled into a subsequent fermentation. This process differs from wine, cider, and spirit manufacturing where the yeast culture is only used once. The serial fermentation process is continued approximately 8-12 times after which a new culture of verified purity and identity is introduced. This increases the likelihood that the yeast remains true to type. Many commercial brewers use proprietary strains the origins of which are usually unknown. Advances in genetic analyses provide a means for probing the origins of brewing yeast strains, and in this study, six historical Irish brewing yeasts from five breweries located within Ireland were assessed. Using Illumina sequencing technology, whole-genome sequencing data were generated. Single nucleotide polymorphism analysis of these data established that the historical Irish brewing yeast group falls within the previously described "Britain" subpopulation Beer 1 clade. Further analysis established that the six historical Irish brewing yeasts separate into two subgroupings, which associated with specific regional locations. Furthermore, the assessment of the six historical Irish brewing yeast phenotypic attributes relevant to brewing correlated within the same regional location groupings. Our data provide further evidence of how brewing requirements associated with specific beer styles have influenced yeast strain selection.

Impact of propagation time on yeast physiology during bottle conditioning of beer on an industrial scale

Bottle conditioning occurs when yeast and a fermentable extract are added to beer prior to packaging. Aside from ethanol and carbon dioxide production, this process can minimize the production of off-flavors and increase the shelf-life of beer. The advantages of bottle conditioning rely on the yeast being able to quickly referment the beer and maintain viability during storage. In this study, a commercial ale yeast was propagated in wort on a large scale (30 hL) for 24 h or 72 h and seeded into pale ale beer for bottle conditioning. We found that yeast propagated until the post-diauxic shift (72 h) provided better longevity in the bottle and improved foam stability compared to the 24 h propagated yeast. At the time of seeding, yeast propagated for 72 h showed an upregulation of proteins involved in cellular respiration and general stress pathways that may indicate responses toward mitigating cellular stress levels.

Assessment of yeast physiology during industrial-scale brewing practices using the redox-sensitive dye resazurin

Beer refermentation in bottles is an industrial process utilized by breweries where yeast and fermentable extract are added to green beer. The beer is refermented for a minimum of 2 weeks before distribution, with the physiological state of the yeast a critical factor for successful refermentation. Ideally, fresh yeast that is propagated from a dedicated propagation plant should be used for refermentation in bottles. Here, we explored the applicability of the fluorescent and redox-sensitive dye, resazurin, to assess cellular metabolism in yeast and its ability to differentiate between growth stages. We applied this assay, with other markers of yeast physiology, to evaluate yeast quality during a full-scale industrial propagation. Resazurin allowed the discrimination between the different growth phases in yeast and afforded a more in-depth understanding of yeast metabolism during propagation. This assay can be used to optimize the yeast propagation process and cropping time to improve beer quality.