Brewing Microbiology

Managing Microbes, Ensuring Quality and Valorising Waste

Annie Hill

• Publisher: Woodhead Publishing
• Year: 2015
• eBook ISBN: 9781782423492
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Brewing Microbiology discusses the microbes that are essential to successful beer production and processing, and the ways they can pose hazards in terms of spoilage and sensory quality.The text examines the properties and management of these microorganisms in brewing, along with tactics for reducing spoilage and optimizing beer quality. It opens with an introduction to beer microbiology, covering yeast properties and management, and then delves into a review of spoilage bacteria and other contaminants and tactics to reduce microbial spoilage.Final sections explore the impact of microbiology on the sensory quality of beer and the safe management and valorisation of brewing waste.- Examines key developments in brewing microbiology, discussing the microbes that are essential for successful beer production and processing- Covers spoilage bacteria, yeasts, sensory quality, and microbiological waste management- Focuses on developments in industry and academia, bringing together leading experts in the field

Part One

Yeast: properties and management

Outline

1. Yeast: an overview

2. Yeast quality assessment, management and culture maintenance

3. Modelling yeast growth and metabolism for optimum performance

4. Advances in metabolic engineering of yeasts

5. Yeast identification and characterization

1

Yeast

An overview

A. Speers¹, and J. Forbes^{2 1}The International Centre for Brewing & Distilling, Heriot-Watt University, Edinburgh, Scotland, UK ²Dalhousie University, Halifax, NS, Canada

Abstract

This chapter discusses the biological structure of yeast and how this structure impacts the brewing process and the ultimate product in terms of flavour, colour and quality. Both ale and lager strains of yeast are used in the brewing process along with, increasingly, ‘brets’. There are subtle differences in each and their respective roles in the brewing process are discussed. Finally, the mechanism of flocculation is examined in some detail.

Keywords

Ale yeast; Cytoplasm; Fermentation; Flocculation; Lager yeast; Plasma membrane; Yeast

1.1. Yeast species/strains used in brewing and distilling

The formal classification of brewing yeasts over the past 50 years has changed enough that many brewing scientists (and most brewers!) avoid using the current genus and species to identify their yeast and simply label them as either ale or lager strains. These yeasts are used to produce most beers – that is, either ‘ales’ or ‘lagers’. Ale is normally made with Saccharomyces cerevisiae that rises to the top of the fermenter at the cessation of fermentation while lager is made with S. carlsbergensis, which settles to the bottom of the tank towards the end of the fermentation. In the past, Barnett, Payne and Yarrow (1983) stated that both types of yeast should be characterized as variants of S. cerevisiae. However, the strains differ in their DNA profiles, ability to ferment melibiose, (ale strains lack melibiase activity) and their maximum growth temperature (lager strains do not grow above 34 °C (Webb, 1977)) and for these reasons, Stewart (1990) has argued that the two types of yeast should be classified as separate species.

Additionally, the increasing importance of a third species, Brettanomyces, has been recognized following the massive growth of the craft brewing movement in the United States. ‘Brets’, as they are termed in the industry, are used in various stages in the production of lambic-type beers. They are considered a spoilage yeast in lager and ale fermentations as they produce volatile phenolic flavours and acetic acid due to their ability to produce off flavours by the production of volatile phenols (Libkind et al., 2011), their ability to produce acetic acid (Wijsman, van Dijken, van Kleeff, & Scheffers, 1984) and their ability to over attenuate products below 1 °Plato (Kumara & Verachtert, 1991). Those involved with the wine industry have spent significant amounts of time and money learning to isolate and characterize Brettanomyces spp. to develop better methods of early detection and eradication (Conterno, Joseph, Arvik, Henick-Kling, & Bisson, 2006; Dias et al., 2003; Oevelen, Spaepen, Timmermans, & Verachtert, 1977). Despite the large amount of negative attention Brettanomyces receives, this interesting microbe has been shown to contribute favourable organoleptic qualities to a number of products and to be of use in several industrial applications.

Belgian lambic beer producers have promoted the unique organoleptic characteristics of Brettanomyces species in concert with other microbes for hundreds of years to produce a beer that is crisp, acidic and refreshing (De Keersmaecker, 1996; Oevelen et al., 1977). However, in comparison to ale and lager yeast less is known about Brettanomyces species employed in brewing.

Since the early 2000s the advances in molecular biology have added to our understanding of the lager yeasts (Libkind et al., 2011; Walther, Hesselbart, & Wendland, 2014). It appears that a newly discovered and sequenced species, S. eubayanus, and S. cerevisiae have combined to form the hybrid lager yeast genome. It is hypothesized that materials containing S. eubayanus strains were imported from Patagonia to Europe where hybridization events have occurred to form the S. carlsbergensis progeny, but more recent studies suggest that the origin of the S. eubayanus strain may be Asia (Bing, Han, Liu, Wang, & Bai, 2014).

Two types of lager yeast are in common use in the brewing industry. The first, Group I, the so-called Saaz type (i.e. ‘Unterhefe No. 1’ isolated by the Carlsberg brewery in 1883) is principally a triplod strain with an almost complete copy of the Saccharomyces cerevisiae genome and slightly more than a diploid copy of S. eubayanus genome (Walther et al., 2014). These same researchers noted that the Group II lager (i.e. the Froberg type, Weihenstephan WS34/70) has a tetraplod with roughly two copies of chromosomes from S. cerevisiae and two from S. eubayanus. It has been suggested that the low fermentation temperatures (e.g. as low as 5 °C) that Group I lagers were exposed to may have driven the difference between Group I and II lager yeasts (Walther et al., 2014).

1.2. Yeast cell structure

Yeast is the most important part of the brewing fermentation process. Yeast converts sugar to alcohol, carbon dioxide and other compounds that influence the flavour and aroma of beer. Brewer’s yeast is a ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Woodhead Publishing Series in Food Science, Technology and Nutrition
• Preface
• Introduction to brewing microbiology
• Acknowledgments
• Part One. Yeast: properties and management
• Part Two. Spoilage bacteria and other contaminants
• Part Three. Reducing microbial spoilage: design and technology
• Part Four. Impact of microbiology on sensory quality
• Part Five. Valorisation of microbiological brewing waste
• Index