13,594
edits
Changes
m
updated italics
Microbial communities found on the outside surface of barley are very diverse and change significantly throughout the malting process, with more diversity occurring further along as the malting process continues. On barley in fields, Gram-negative bacteria (especially ''Erwinia herbicola'') are abundant. Climate is said to have the most impact on which species grow in barley fields. For example ''Fusarium'' species are encouraged by high humidity, and are associated with mycotoxins and gushing problems in beer. During dry storage of barley, spore forming bacteria tend to survive. Xerophilic fungi (fungi that doesn't need much water) also survive on dry barley during storage <ref name="Lievens1">[https://lirias.kuleuven.be/bitstream/123456789/323403/2/Just%C3%A9%20et%20al.%202011_Microflora%20during%20Malting%20of%20Barley%20Overview%20and%20Impact%20on%20Malt%20Quality.%20Brewing%20Science%2064,%2022-31..pdf Microflora during Malting of Barley: Overview and Impact on Malt Quality. A. Justé, S. Malfl iet, M. Lenaerts, L. de Cooman, G. Aerts, K. A. Willems and B. Lievens. 2011.]</ref>.
Microbial communities on the husks of barley change quite a bit during the malting process. It is thought that the factors affecting this are the initial microbe populations, interactions between species, the variances in the malted barley characteristics/processes, and additives. Different malting houses are likely to form "in-house" microflora populations. The first step in malting, which is steeping, sees the first large change in microbial populations. The steeping process favors lactic acid bacteria (LAB), which are seen only in very small numbers before steeping. Particularly these are ''Leuconostoc'' species. In the case of yeasts, ''Basidiomycota'' fungi grow, as well as ''Fusarium'' <ref name="Lievens1"></ref>.
The second step of malting, which is germination, sees starches converted to sugars, which causes microbial populations to increase once again. Where ''Leuconostoc'' species of bacteria were dominate during steeping, the germination process is where [[Lactobacillus]] species begin to dominate the microbial community. A greater diversity of species also occurs during this step in malting. As far as fungi, ''Ascomycetous'' yeasts begin to dominate, where as ''Alternaria'' and ''Cladosporium'' decline <ref name="Lievens1"></ref>.
During kilning, microbial populations are reduced by a factor of 10-100, but are still higher than that of field barley. The high degree of variability is dependent on the kilning temperature and procedure. Heat resistant microbes, perhaps by forming biofilms, can survive the hot temperatures. These include molds such as ''Rhizopus'' and ''Mucor'' species <ref name="Lievens1"></ref>.
===Malted Barley===
''Enterobacter spp'' specifically have been identified as beer spoilage agents, which produce high amounts of 2,3-Butanediol (buttery taste <ref>[http://www.thegoodscentscompany.com/data/rw1161171.html The Good Scents Co. 2,3-butane diol. Retrieved 10/15/2015.]</ref>), as well as acetoin (also buttery taste <ref>[http://www.thegoodscentscompany.com/data/rw1007331.html The Good Scents Co. Acetoin. Retrieved 10/16/2015.]</ref>, lactic acid, acetic acid, succinic acid, high alcohols such as n-propanol, iso-butanol, D-amyl-alcohol, isoamyl alcohol, and sulfur compounds such as dimethyl sulfide (DMS), all under both aerobic and semi-aerobic conditions <ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1992.tb01126.x/epdf Synthesis of Aroma Compounds By Wort Enterobacteria During First Stage of Lambic Fermentation. H. Martens, E. Dawoud, and H. Verachtert. Jan 1992.]</ref><ref name="Bamforth"></ref>. ''Enterobacter'' is not inhibited by hops, but is inhibited by ethanol and a pH of 4.4. ''Acinetobacter'' has also been shown to produce DMS in wort, however they are strictly aerobic and encountered in much smaller amounts than ''Enterobacter'' in brewing <ref>[http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1974.tb03629.x/abstract WORT ENTEROBACTERIA—A REVIEW. F. G. Priest, M. A. Cowbourne and J. S. Hough. 2013.]</ref>.
Interestingly, the study also found that the dominate genera of microbes was different between the two years sampled. In 2010, there were more ''Firmicutes'' species (which includes LAB) and more ''Actinobacteria'', and less ''Bacteroidetes''. In 2011, the reverse was found with fewer ''Firmicutes'' and ''Actinobacteria'', and more ''Bacteroidetes'' <ref name="Lievens3">[https://www.youtube.com/watch?v=5mttD027PMU Bart Lievens - Bacterial community dynamics during industrial malting, at the Belgian Brewers Conference 2015.]</ref> (~15 mins in).
The study examined LAB populations specifically due to their potential to help with malt stability and quality <ref>[http://www.researchgate.net/profile/Arja_Laitila/publication/7062169_Lactobacillus_plantarum_and_Pediococcus_pentosaceus_starter_cultures_as_a_tool_for_microflora_management_in_malting_and_for_enhancement_of_malt_processability/links/00b7d529ed5568640a000000.pdf Lactobacillus plantarum and Pediococcus pentosaceus Starter Cultures as a Tool for Microflora Management in Malting and for Enhancement of Malt Processability. ARJA LAITILA, HANNELE SWEINS, ARVI VILPOLA, ERJA KOTAVIITA, JUHANI OLKKU, SILJA HOME, AND AULI HAIKARA. 2006.]</ref>. ''Streptococcus'' was the most abundant genus of bacteria in all samples. In 2010, ''Lactobacillus'' was more abundant than it was in 2011. ''Lactococcus'' and ''Weisella'' were more abundant in 2011 than in 2010. Maltster 1 had a greater abundance of both ''Lactococcus'' and ''Weisella'' in 2011 over Maltster 2. In 2010, ''Lactobacillus'' was more abundant for Maltster 2 than it was for Maltster 1. This showed that microbial populations differ not only between malt houses, but also between barley harvest years <ref name="Lievens3"></ref> (~17 mins in).