‘Get the simple things right and the big things take care of themselves’ studies on brewing yeast, fermentation and draught beer : 1979-2025

Abstract

The work reported here between 1979 and 2025, spans the heyday and decline of brewing science in the UK. The brewing industry was in rude health until the publication in 1989 of ‘Beer Orders’ by Monopolies and Mergers Commission which removed the ‘tie’ between breweries and pubs. This removed large swathes of profitability and began the long march to decline. Technical centres were downsized or closed and by 2000 the ‘big six’ UK brewers had either ceased brewing or were owned by brewing companies from the USA, Belgium and South Africa. Two themes are discussed: brewing yeast and fermentation (Chapters 2-5) and draught beer quality (Chapter 6). The guiding principle to both studies is to ‘get the simple things right and the big things take care of themselves’. The studies on yeast and fermentation were mostly performed at Bass, the biggest of the then ‘big six’ UK brewers. Although commercially driven, there were opportunities to publish less sensitive work. Indeed, the various brewing conferences around the world encouraged this and brewing science flourished with unspoken competition between brewing companies for publications of quality, impact and influence. The flavour and aroma of beer is important. It should be consistent, balanced and reflect the brand specification. The industry was in significant growth in the late 70s and, consequently, new large scale fermentation processes were introduced. This had an impact on the production by yeast of esters and higher alcohols during fermentation which distorted the aroma of the beer. The work outlined in Chapter 2 sought to better understand the synthesis of these metabolites and to be able to better control their formation. In both instances, their synthesis reflected the need to balance the flux of intermediary metabolic cofactors, acetyl CoA/CoA (esters) and NADH/NAD (higher alcohols). Yeast does what it does for good metabolic reasons and not to please the brewer! Yeast is an important contributor to the distinctiveness of beer, with different strains making different beers. A key part of Chapter 3 is the process that was developed to assure the identity and microbiological quality of yeast that was periodically ‘supplied’ to the Bass breweries. It was ahead of its time using cryogenic long-term storage of production yeasts and DNA fingerprinting to validate (blind) the identity of each strain. Allied to this work, is a study of the genetic instability of a major production yeast used in two breweries, separated by 280 miles and some 10 years apart. Other work considers the introduction of ATP bioluminescence to validate in real time the cleaning of brewery vessels. This was a cultural change as the checking of the effectiveness of the clean was performed by process operators and not the ‘white coats’ from the Quality department. Adoption of the technology and its delivery is now the norm in global brewing industry. The final piece in this Chapter describes some opportunist research that explored the unexpected metabolism by brewing yeasts of the sugar alcohol, mannitol. Brewery fermentations need to be efficient, requiring sufficient but not excessive yeast growth. The work in Chapter 4 considers the role of small amounts of oxygen added at the beginning of fermentation for the synthesis of sterols, a lipid class that determines the extent of yeast cell division and growth. Evidence is presented that at the beginning of fermentation, the yeast cell is unable to transport exogenous sugars and that the metabolic fuel for this process is provided by glucose from the breakdown of the storage carbohydrate glycogen. At the time, the efficiency of fermentation and its management was a major driver of research in the brewing industry. Although much of the work in Chapter 5 was developed in the laboratory, we were fortunate that elements were evaluated at a production scale. Initial work explored the relationship between oxygen and yeast growth. This demonstrated that yeast strains require the addition of an optimal level of oxygen to achieve the required fermentation performance and efficiency. Excess oxygen resulted in excess yeast growth and less ethanol formation. An innovative approach evaluated at a plant scale considered a more direct approach with the oxygenation of yeast. Regrettably, a change in the approach for beer taxation undermined this work which was not progressed further. Brewery fermentations are unusual in recycling yeast from one fermentation to the next. This can pose problems, as yeast quality can become compromised. Chapter 5.3 describes a ‘warm cropping’ process where yeast is recovered (‘cropped) from fermenter two days earlier than is usual. This approach improved the physiological quality of the yeast which – in extensive series of production fermentations – resulted in a step change improvement in quality metrics. Further work on the cropping process considered the heterogeneity of yeast cell populations. The age profile (and associated cell size) of individual cells was of interest together with their selection during cropping and subsequent performance in brewery fermentations. On leaving Bass - now Molson Coors - in 2004, brewing science in the UK was sadly in decline. Consultancy called and I became a ‘portfolio professional’ doing a bit of this and a bit of that. A part time role at Heriot-Watt University was enjoyable but after eight years there was appeal in working closer to home and, if possible, doing some research. A role at the University of Nottingham achieved both objectives. Although funding for yeast research was difficult, a new direction loomed. As a consumer, I was aware that the quality of draught beer can be variable and occasionally poor. With previous experience at Bass of dispense technology coupled with being a microbiologist, it made sense to develop a research programme into the factors that impact on draught beer quality. These studies are reported in Chapter 6 and, like some of the yeast studies, benefit from taking the work out of the laboratory into the ‘real world’. Draught beer systems are invariably contaminated with non-pathogenic microorganisms (yeasts and bacteria) that can grow in beer. Low levels are not a concern but the quality (flavour, aroma, clarity) of draught beer becomes progressively compromised with greater numbers of microorganisms which attach to surfaces in the dispense system as biofilms. Microbial contamination is managed by hygienic practices, primarily line cleaning where the system is flushed with dilute caustic solution. This is the weak link as the process is tedious and the recommended weekly clean can – in many accounts - slip to two weeks or more. Measurement of quality using a ‘forcing test’ (Chapter 6.3) was used with samples from public houses (Chapter 6.4) confirming that beer quality ranged from ‘excellent’ through ‘acceptable’ to ‘poor and ‘unacceptable’. Other work modelled biofilm attachment and growth by microorganisms in draught beer (Chapter 6.5). The microorganisms in different styles of draught beer from multiple public houses in different cities and towns exhibited a core microflora (e.g. Brettanomyces, Acetobacter) with some specific to individual styles (Chapter 6.6). In a parallel study, microflora were inoculated into different commercial lagers and found to vary in susceptibility to spoilage. Greater spoilage was associated with beers of higher pH and nutrient availability (Chapter 6.7). In a similar study, the susceptibility to spoilage of alcohol free and low alcohol beers was evaluated. These beers were more spoilable (rate and extent) than conventional ‘alcoholic beer’. Although alcohol free beers (AFBs) may require tuning for effective pasteurisation, a greater concern is their delivery in public houses using draught dispense. With the growth of the sector, brand owners are increasingly keen to serve their beers in this way as it is more profitable than with bottles or cans. This is a concern with these beers being more easily spoilt by microorganisms which will compromise quality. A very different concern is the absence of alcohol will allow the growth of some contaminating pathogens in alcohol free beer which is a significant concern for food safety. The recommendation that AFBs are dispensed by bespoke, stand-alone dispense systems has had limited take up which suggests there is need for other approaches to minimise this particular consumer risk