BST325 — Microbiology of Beer: Lecture Note

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LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS • Course code: BST325 • Course title: Microbiology of Beer • Course credit load: 3 Series 1: Microbial Spoilage in Brewing Series outline • Part 1: Occurrence and Frequency of Brewing Micro-organisms o 1.1 Types of micro-organisms in brewing o 1.2 Sources of contamination in raw materials and equipment o 1.3 Frequency and monitoring of microbial presence • Part 2: Biology of Brewing Micro-organisms o 2.1 Characteristics of spoilage organisms o 2.2 Growth conditions and survival strategies o 2.3 Impact on brewing processes • Part 3: Detection and Identification Methods o 3.1 Traditional microbiological techniques o 3.2 Selective media and viability testing o 3.3 Modern laboratory methods for detection • Part 4: Spoilage Effects on Brewing Process and Product Quality o 4.1 Influence on fermentation and flavour o 4.2 Physical and chemical changes in beer o 4.3 Case studies of spoilage incidents • Part 5: Control and Prevention Strategies o 5.1 Cleaning-in-place (CIP) and sanitation practices o 5.2 Good manufacturing practice (GMP) in brewing o 5.3 Integration with hazard analysis and critical control points (HACCP)

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Introduction Beer is one of the most widely consumed beverages in the world, yet its production is highly vulnerable to microbial contamination. Even small populations of unwanted micro-organisms can compromise flavour, aroma, and stability, leading to spoilage and economic loss. For brewers, understanding how and why these organisms occur is essential to maintaining product quality and consumer trust. The aim of this Series is to equip you with the knowledge and skills to identify, analyse, and manage microbial spoilage in brewing, from its occurrence and biology to its detection, impact, and control. We shall commence this Series by examining the occurrence and frequency of brewing micro-organisms. Then, we will explore the biology of these spoilage organisms and their survival strategies. Following that, we will consider methods of detection and identification, before moving on to the spoilage effects on brewing processes and product quality. Finally, we will wrap up by discussing control and prevention strategies, including cleaning-in-place, good manufacturing practice, and hazard analysis. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1 define the types and sources of micro-organisms associated with brewing spoilage, • SLO 1.2 explain the biological characteristics and growth conditions of spoilage organisms, • SLO 1.3 demonstrate methods for detecting and identifying brewing micro-organisms, • SLO 1.4 analyse the effects of microbial spoilage on brewing processes and product quality, and • SLO 1.5 evaluate control and prevention strategies such as CIP, GMP, and HACCP in brewing. 1.1 Occurrence And Frequency Of Brewing Micro-organisms Brewing is a biological process that relies on carefully managed yeast activity. However, unwanted micro-organisms (living microscopic entities such as bacteria, wild yeasts, and moulds) can enter the process at different stages. These organisms are considered contaminants because they interfere with the desired fermentation and spoil the final product. Their occurrence is influenced by raw materials, equipment hygiene, and environmental conditions. Fill in the blank: Micro-organisms that interfere with brewing are called ________. 1.1.1 Types of micro-organisms in brewing The main spoilage organisms include lactic acid bacteria (bacteria that produce lactic acid, leading to sour flavours), wild yeasts (yeasts other than the intended brewing strain, which can

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS cause off-flavours and poor fermentation), and moulds (fungi that grow on damp surfaces and raw materials). Each type has distinct effects on beer quality. Diagram showing different types of brewing micro-organisms (bacteria, wild yeast, mould). Figure 1.1 Types of brewing micro-organisms 1.1.2 Sources of contamination in raw materials and equipment Spoilage organisms often originate from raw materials such as malt, hops, and water. They may also be introduced through equipment surfaces if cleaning is inadequate. For example, lactic acid bacteria can survive in malt dust, while moulds thrive in damp storage areas. Equipment such as fermenters, pipes, and bottling lines can harbour biofilms if not properly sanitised. Fill in the blank: Spoilage organisms can survive in malt dust and ______ storage areas.

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Image showing contaminated brewing equipment with microbial growth. Plate 1.2 Contaminated brewing equipment 1.1.3 Frequency and monitoring of microbial presence The frequency of contamination depends on the level of hygiene and control measures in place. Regular monitoring is essential to detect micro-organisms early. Brewers often use selective media to test samples from raw materials, fermenters, and finished beer. Monitoring ensures that contamination is identified before it affects product quality. Fill in the blank: Brewers use ______ media to test samples for microbial contamination. Box 1.1 Common Monitoring Practices in Breweries Maintaining beer quality and preventing spoilage requires a comprehensive monitoring program that spans the entire production process, from raw material intake to final packaging[cite: 1]. This involves a combination of physical inspection, chemical analysis, and microbiological testing. • Sampling raw materials: All incoming ingredients, particularly malt and hops, can carry environmental micro-organisms (like mould spores or wild yeast). Brewers must inspect and sample these materials upon arrival to ensure they meet quality specifications and are free from contamination[cite: 1, 2]. • Swabbing equipment surfaces: This is a critical component of a Hazard Analysis and Critical Control Points (HACCP) plan. Regular swabbing of vessel interiors (after CIP—

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Clean-In-Place procedures), hoses, valves, and filler heads helps verify the effectiveness of sanitation and detect the presence of biofilms, which can harbour spoilage organisms[cite: 3]. • Testing fermenter contents: The fermentation process itself must be closely monitored. Brewers routinely take samples from fermenters and bright beer tanks to check for gravity, pH, and, crucially, to perform microbiological plating or ATP testing to confirm the purity of the yeast culture and detect any bacterial or wild yeast contamination early[cite: 2]. • Analysing finished beer: The final check before packaging or kegging is the comprehensive analysis of the finished product. This includes sensory evaluation (tasting for off-flavours) and final microbiological testing to ensure the beer is shelf-stable and meets all quality standards before release to the consumer[cite: 1, 3]. Pilot questions 1.1 1. Which micro-organisms are the most common spoilage agents in brewing? 2. What raw material can harbour lactic acid bacteria? 3. What type of yeast is considered a contaminant in brewing? 4. Why is monitoring essential in brewing microbiology? 5. Which equipment surfaces are most prone to microbial biofilm formation? 1.2 Biology Of Brewing Micro-organisms Brewing micro-organisms are diverse in their biology, and their ability to spoil beer depends on their structural features, metabolic activities, and adaptability to brewing environments. By studying their biology, brewers can anticipate how these organisms behave and design strategies to control them. Fill in the blank: The ability of micro-organisms to spoil beer depends on their ______ features and metabolic activities. 1.2.1 Characteristics of spoilage organisms Spoilage organisms such as lactic acid bacteria (micro-organisms that convert sugars into lactic acid, producing sour flavours), wild yeasts (yeasts not intended for brewing, which compete with brewing strains), and moulds (fungi that grow on damp surfaces and raw materials) share certain traits. They often tolerate alcohol, low pH, and limited nutrients, making them well-suited to survive in beer.

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Diagram showing structural features of lactic acid bacteria, wild yeast, and mould. Figure 1.3 Structural features of spoilage organisms 1.2.2 Growth conditions and survival strategies Spoilage organisms thrive under specific growth conditions such as warm temperatures, nutrient-rich wort, and oxygen availability. Their survival strategies include forming biofilms (communities of micro-organisms attached to surfaces), producing spores (resistant structures that survive cleaning), and adapting to stress conditions like ethanol presence. These strategies make them persistent threats in breweries. Fill in the blank: Spoilage organisms can survive cleaning by forming ______ on equipment surfaces.

LA-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Image showing microbial biofilm on a brewing pipe. Plate 1.4 Biofilm formation in brewing equipment 1.2.3 Impact on brewing processes The biological activities of spoilage organisms directly affect brewing. Lactic acid bacteria produce acids that alter flavour and reduce stability. Wild yeasts compete with brewing yeast, leading to incomplete fermentation and undesirable aromas. Moulds can introduce toxins and off-flavours. These impacts compromise both the brewing process and the quality of the final beer. Fill in the blank: Wild yeasts compete with ______ yeast, leading to incomplete fermentation. Box 1.2 Biological Impacts of Spoilage Organisms While the brewing process relies on the controlled activity of Saccharomyces yeast, the presence of other micro-organisms can disrupt fermentation and severely degrade the sensory quality and shelf-life of the beer. These spoilage organisms impact the beer through competition for nutrients, the production of unwanted metabolites, and the degradation of beer components[cite: 1]. • Lactic acid bacteria (LAB):

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