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.

Aims: The aim of this study was to perform a detailed characterization of bacteriocins produced by lactic acid bacteria (LAB) isolated from malted barley. Methods and Results: Bacteriocin activities produced by eight LAB, isolated from various types of malted barley, were puri®ed to homogeneity by ammonium sulphate precipitation, cation exchange, hydrophobic interaction and reverse-phase liquid chromatography. Molecular mass analysis and N-terminal amino acid sequencing of the puri®ed bacteriocins showed that four non-identical Lactobacillus sakei strains produced sakacin P, while four Leuconostoc mesenteroides strains were shown to produce bacteriocins highly similar or identical to leucocin A, leucocin C or mesenterocin Y105. Two of these bacteriocin-producing strains, Lb. sakei 5 and Leuc. mesenteroides 6, were shown to produce more than one bacteriocin. Lactobacillus sakei 5 produced sakacin P as well as two novel bacteriocins, which were termed sakacin 5X and sakacin 5T. The inhibitory spectrum of each puri®ed bacteriocin was analysed and demonstrated that sakacin 5X was capable of inhibiting the widest range of beer spoilage organisms. Conclusions: All bacteriocins puri®ed in this study were class II bacteriocins. Two of the bacteriocins have not been described previously in the literature while the remaining puri®ed bacteriocins have been isolated from environments other than malted barley. Signi®cance and Impact of the Study: This study represents a thorough analysis of bacteriocin-producing LAB from malt and demonstrates, for the ®rst time, the variety of previously identi®ed and novel inhibitory peptides produced by isolates from this environment. It also highlights the potential of these LAB cultures to be used as biological controlling agents in the brewing industry.

The microflora of malting and mashing was investigated with emphasis on the numbers and types of lactic acid bacteria (LAB)present during these processes. A traditional small-scale floor malthouse, a modern, pneumatic large-scale malthouse and two brewhouses, each ofwhich were utilised for the manufacture of stout and lager brews were studied. The bacterial population of dried, stored barley for malting was dominated by Gram-coliforms and pseudomonads, with LAB constituting a small minority of the total viable count. In both malthouses, the microbial count increased dramatically during barley steeping. Although pseudomonads still dominated, a significant increase in the LAB population was observed. Viable counts decreased slightly towards the end of germination and were reduced by >98%for all groups during kilning. Final counts of LAB on the kilned and screened malt were approximately 10s, comprising 0.5% of the total viable microbial count. While leuconostocs were the predominant LAB detected in the early stages of the process, there was a discernible shift towards homo-fermentative lactobacilli during barley germination. Viable counts of LAB during lager and stout brewhouse mashes in two breweries indicated that initial microbial counts after mashing-in were high (from 105-107 CFWg) and these decreased steadily during the mash programme. In the initial stages of mashing, the LAB population consisted of an equal mixture of lactobacilli and pediococci, but lactobacilli dominated the later stages of the mash. The pre-lauter viable count of LAB was generally <10 CFWg.

Thirty-three putative inhibitor-producing lactic acid bacteria (LAB) were isolated from malted barley based on their ability to inhibit groivth oftioo indicator strains. Eleven of the inhibitorproducing LAB produced an antimicrobial activity which zvas active across a wide pH range, relatively insensitive to heat treatment rohile sensitive to treatment ivith proteolytic enzymes indicating that the inhibitory compounds are proteinaceous in nature and therefore bacteriocinlike inhibitory substances. Ten of these eleven malt isolates were observed to secrete the inhibitory compounds into the cell-free supernatant with optimal production occurring in the late exponential growth phase. The inhibitory spectra of these isolates included various Grampositive bacteria among which a variety of beer-spoiling bacteria.

Background Lactobacillus brevis is a member of the lactic acid bacteria (LAB), and strains of L. brevis have been isolated from silage, as well as from fermented cabbage and other fermented foods. However, this bacterium is also commonly associated with bacterial spoilage of beer. Results In the current study, complete genome sequences of six isolated L. brevis strains were determined. Five of these L. brevis strains were isolated from beer (three isolates) or the brewing environment (two isolates), and were characterized as beer-spoilers or non-beer spoilers, respectively, while the sixth isolate had previously been isolated from silage. The genomic features of 19 L. brevis strains, encompassing the six L. brevis strains described in this study and thirteen L. brevis strains for which complete genome sequences were available in public databases, were analyzed with particular attention to evolutionary aspects and adaptation to beer. Conclusions Comparative genomic analysis highlighted evolution of the taxon allowing niche colonization, notably adaptation to the beer environment, with approximately 50 chromosomal genes acquired by L. brevis beer-spoiler strains representing approximately 2% of their total chromosomal genetic content. These genes primarily encode proteins that are putatively involved in oxidation-reduction reactions, transcription regulation or membrane transport, functions that may be crucial to survive the harsh conditions associated with beer. The study emphasized the role of plasmids in beer spoilage with a number of unique genes identified among L. brevis beer-spoiler strains.