Quantitative and qualitative studies of the microflora of barley malt production

167

While beer provides a very stable microbiological environment, a few niche microorganisms are capable of growth in malt, wort and beer. Growth of mycotoxin‐producing fungi during malting, production of off‐flavours and development of turbidity in the packaged product due to the growth and metabolic activity of wild yeasts, certain lactic acid bacteria (LAB) and anaerobic Gram negative bacteria, impact negatively on beer quality. It follows that any means by which microbial contamination can be reduced or controlled would be of great economic interest to the brewing industry and would serve the public interest. There has been an increasing effort to develop novel approaches to minimal processing, such as the exploitation of inhibitory components natural to raw materials, to enhance the microbiological stability of beer. LAB species, which occur as part of the natural barley microbiota, persist during malting and mashing, and can play a positive role in the beer‐manufacturing process by their contribution to wort bioacidification or the elimination of undesirable microorganisms. Other naturally occurring components of beer that have been valued for their preservative properties are hop compounds. It may be possible to enhance the antimicrobial activities of these compounds during brewing. Some yeast strains produce and excrete extracellular toxins called zymocins, which are lethal to sensitive yeast strains. Yeast strains resistant to zymocins have been constructed. Imparting zymocinogenic activity to brewing yeast would offer a defence against wild yeasts in the brewery. Thus, the antimicrobial properties of naturally occurring components of raw materials can be exploited to enhance the microbial stability of beer.

Section: Propertiesmentioning

confidence: 99%

“…LAB can be found in brewing materials at almost every stage of the malting and brewing process, from the standing barley crop to the finished beverage 57,85,147 . These bacteria are present as part of the natural barley microbiota, and persist during malting and mashing 145 .…”

Section: Introductionmentioning

confidence: 99%

Enhancing the Microbiological Stability of Malt and Beer - A Review

Vaughan

O'Sullivan

Sinderen

2005

167

“…Finally, the removal of water during kilning halts both grain and microbial activities. However, kilning has little effect on the viable counts of microbes, which are generally higher in the finished malt than that in the native barley 31,32,46 . The kilning regime has been identified as a significant factor in controlling the microbial community 52 .…”

Section: Introductionmentioning

confidence: 97%

“…In addition to germinating barley, the malting process involves another metabolically active component: the diverse microbial community that naturally colonizes the grains. The indigenous community harbours a wide range of microbes including numerous species of Gram-negative and -positive bacteria, yeasts and filamentous fungi 17,20,32,41,46 . In addition, each process step can be a source of additional microbes and their metabolites 32,45 .…”

Section: Introductionmentioning

confidence: 99%

Indigenous Microbial Community of Barley Greatly Influences Grain Germination and Malt Quality

Laitila

Kotaviita

Peltola³

et al. 2007

The present study was carried out to investigate the impacts of bacterial and fungal communities on grain germination and on the malting properties of good‐quality two‐row barley. In order to suppress the growth of bacterial and/or fungal communities, various antibiotics were added to the first steeping water of barley. This study was also designed to explore the dynamics of the bacterial community in the malting process after antimicrobial treatments by polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE). The diverse microbial community played an active role in the malting ecosystem. Even previously undescribed bacterial species were found in the malting ecosystem. Suppression of the bacterial community mainly consisting of Gram‐negative bacteria was advantageous with respect to grain germination and wort separation. In addition, more extract was obtained after antibacterial treatments. The fungal community significantly contributed to the production of microbial β‐glucanases and xylanases, and was also involved in proteolysis. An improved understanding of the complex microbial community and its role in malting enables a more controlled process management and the production of high quality malt with tailored properties.

“…Indeed, LAB can be found in brewing materials at almost every stage of the malting and brewing process, from the standing barley crop to the finished beverage 13,17,28,33 . These bacteria occur as part of the natural barley micro-biota, and persist during malting and mashing 29,35 due to their aero tolerant nature and tolerance of low pH and high ethanol levels.…”

Section: Introductionmentioning

confidence: 99%

Effects of Lysozyme on the Microbiological Stability and Organoleptic Properties of Unpasteurized Beer

Silvetti

Brasca

Lodi

et al. 2010

Lysozyme is an antimicrobial enzyme that could be applied to counteract those bacterial species which, due to their own metabolic activity, possess notable beer spoilage ability and lead to loss of beer quality. Experiments were carried out to assess lysozyme potential to prevent the growth of beer spoilage bacteria, and to verify the effect of lysozyme on the microbiological stability and sensory characteristics of unpasteurized beer. Eight replicates, all from the same lot of Italian beer, were treated with 0 and 100 ppm lysozyme. Microbiological analyses were conducted bimonthly to investigate the presence of spoilage bacteria. Sensory analyses were performed to determine whether there were any significant differences in sensory impressions between beers produced with and without lysozyme. Lysozyme exerted a strong inhibitory action on the lactic acid bacteria (LAB) present in the beer and was very stable throughout the shelf life. Sensory tests revealed no unfavourable influence on beer flavour when using lysozyme. Indeed, the shelf life of beer with added lysozyme proved to be extended. Even as late as 1 month after the expiry date it still met with the panellists' approval. Lysozyme may be regarded as an effective agent for preventing microbiological contamination and prolonging the stability of unpasteurized beer.