Beer spoilage bacteria and hop resistance

166

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: Introductionmentioning

confidence: 99%

Enhancing the Microbiological Stability of Malt and Beer - A Review

Vaughan

O'Sullivan

Sinderen

2005

166

167

“…Most hazardous for the brewing industry are the LAB belonging to the genera Lactobacillus and Pediococcus, because they can produce haze or rope and cause unpleas- ant flavour changes such as sourness and atypical odour 13 . Various contamination levels were present among the breweries analyzed due to the hygiene practices applied.…”

Section: Molecular Methodsmentioning

confidence: 99%

“…Beer is a poor and rather hostile environment for most microorganisms: its ethanol concentration is usually around 4-5% v/v and its pH ranges from 3.8 to 4.7. Only a few bacteria are able to grow under such inhospitable conditions and are able to spoil the beer 13 . To prevent microbial contamination during the production process, the microbiological purity of brewing yeast starters is a necessary condition to maintain high product quality.…”

Section: Introductionmentioning

confidence: 99%

Microbiological Analyses of Dry and Slurry Yeasts for Brewing

Manzano

Giusto

Bartolomeoli

et al. 2005

Classical microbiological methods in association with molecular methods (DNA amplification, Temperature Gradient Gel Electrophoresis (TGGE) and Denaturing Gradient Gel Electrophoresis (DGGE) were used. These methods, developed to rapidly analyze microbial communities on the basis of sequence-specific separation of DNA amplicons, allowed the detection of DNA differences in the amplicons tested and the identification of the strains analyzed by the comparison of unknown sequences with sequences of known species. TGGE allowed the comparison of the different Saccharomyces cerevisiae strains used in brewing while DGGE allowed the identification of lactic acid bacteria (LAB) in beer. These methods are a reliable tool for fast comparison of strains of Saccharomyces cerevisiae collected from different craft breweries where they were used as starters to check the presence of possible yeast contaminants in the brewing process and for rapid LAB identification.

“…L. coryniformis, L. casei and L. plantarum are other important Lactobacillus species which have been reported to spoil beer 6,38 with a frequency of beer spoilage incidents of 3, 2 and 1% respectively 2,47,48 . Lactobacillus species cause high turbidity, hazy appearance, unpleasant flavours and a high level of diacetyl in beer 42 .…”

Section: Introductionmentioning

confidence: 99%

Occurrence of Pectinatus and Megasphaera in the Major UK Breweries

Paradh

Mitchell

Hill

2011

The occurrence of beer spoilage bacteria belonging to the genera Pectinatus and Megasphaera in ten major UK breweries was investigated. The sampling points were selected from fermentation areas, beer conditioning areas and beer bottling and canning sites. Multiplex PCR methodology was used for detection of three Pectinatus and three Megasphaera species using speciesspecific primers. The presence of six Lactobacillus species was also examined. Overall, 117 samples were analysed from ten breweries; six samples were positive for the presence of Pectinatus species and three samples were positive for the presence of Megasphaera species, while 34 samples were positive for the presence of Lactobacillus species. Lactobacillus species appeared to be the major potential spoilage microorganisms. Although none of the actual beer samples were found to be positive for Pectinatus and Megasphaera species, their occurrence in aerobic brewery environments indicates sanitation problems and revealed the presence of highly established biofilms in some breweries.