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Yeast Supply, Fermentation and q Handling - Insights, Best Practice and 3 Consequences of Failure

David E. Quain

International Centre for Brewing Science, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, UK.

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https://doi.org/10.21775/9781910190616.03

Abstract

The bottom line in brewery fermentation is that consistency is paramount. Whatever the scale of the operation, excellent yeast quality is a fundamental process requirement to ensure good and sustainable beer quality. The recycling of yeast across numerous fermentations adds complexity and biological stress. It is recommended that this be compensated by application of best practice in yeast supply/propagation, pitching, fermentation and storage. Craft brewers operating at a small scale and without recycling should be conscious of best practice for the rehydration of active dried yeast.

Introduction

With the exception of hybrid lager strains (Sac- charomycespastorianus), domesticated yeast used in brewing, baking, distilling and most wine making is branded taxonomically as Saccharomyces cerevisiae. This loosely translates to ‘sugar mould' (saccharomyces) and ‘beer' (cerevisiae). Given its on-going contribution, yeast can justifiably claim to be one of humankind's best friends. Indeed, in addition to its role in the fermentation of sugars, budding yeast has in recent decades become the pre-eminent model laboratory microorganism. This combined contribution to humankind has been neatly headlined (Duina et al., 2014) as, ‘a kitchen companion for centuries, S. cerevisiae has seen exponential growth (pun intended) as a laboratory companion over the past half century.

A more recent turning point was the groundbreaking sequencing of the genome of S. cerevisiae S288C (Goffeau et al., 1996). Not surprisingly, since then S. cerevisiae has seen accelerated use as a model organism. So much so that Botstein and Fink (2011) noted ‘that yeast has graduated from a position as the premier model for eukaryotic cell biology to become the pioneer organism that has facilitated the establishment of the entirely new fields of study called ‘functional genomics' and ‘systems biology.' These new fields look beyond the functions of individual genes and proteins, focusing on how these interact and work together to determine the properties of living cells and organisms.'

Stunning contemporary examples of yeast as a ‘pioneer organism' include the creation of a synthetic chromosome III (foreshadowing the possibility of entirely synthetic yeast genomes) (Pennisi, 2014), the successful replacement of defective yeast genes with their human counterparts (Kachoo et al., 2015) and diverse ‘engineered' yeasts on the road to producing - amongst other things - penicillin, opiates and anti-malarial drugs.

In the world of brewing yeast things have been a little less newsworthy. That said, the genome sequence of the widely used S. pastorianus Weihen- stephan 34/70 was published in 2009 (Nakao et al., 2009) and that of the first pure culture lager yeast

(Carlsberg Unterhefe No.1) in 2014 (Walther et al., 2014). Recently, there has been a flurry of excitement around the hybrid genome of lager yeast, S. pastorianus, comprising S. cerevisiae and another (cryotolerant) yeast. The identification of Saccha- romyces eubayanus from southern beech forests in Patagonia (Libkind et al., 2011) as the ‘other' yeast caused something of a stir in the wider news media. In particular, the disconnect between lager brewing originating in Bavaria in the fifteenth century but predating trans-Atlantic trade triggered a hunt for a sources of S. eubayanus closer to Germany. Although the route is still by no means clear, it is suggested to ‘be the product of multiple long-distance dispersal events' (Gayevskiy and Goddard, 2015), this yeast having been found in Tibet (Bing et al., 2014) and New Zealand (Gayevskiy and Goddard, 2015) (see Chapter 4).

Although a fascinating one-off, there is a wider ‘halo effect' of stretching academic research that can be overlaid to aid the understanding of yeast during brewing fermentation and associated handling. This is fitting as globally brewing research is sadly in decline. There are a few hotspots but the halcyon days of the 1980s for applied brewing yeast research are no more. However much can be learned and applied from fundamental studies and related worlds such as biofuel and wine research.

This various process steps reviewed in this article are summarized in Fig. 3.1.

Process overview

Figure 3.1 Process overview.

 
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